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diff --git a/gcc-4.2.1-5666.3/gcc/doc/invoke.texi b/gcc-4.2.1-5666.3/gcc/doc/invoke.texi new file mode 100644 index 000000000..f8f81b46d --- /dev/null +++ b/gcc-4.2.1-5666.3/gcc/doc/invoke.texi @@ -0,0 +1,15136 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, +@c 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin INCLUDE +@include gcc-vers.texi +@c man end + +@c man begin COPYRIGHT +Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcc +@settitle GNU project C and C++ compiler +@c man begin SYNOPSIS +gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] + [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] + [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] + [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] + [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. + +@c APPLE LOCAL begin manual +In Apple's version of GCC, both @samp{cc} and @samp{gcc} are actually +symbolic links to a compiler named like gcc-@var{version}. +Similarly, @samp{c++} and @samp{g++} are links to a compiler named like +g++-@var{version}. + +Note that Apple's GCC includes a number of extensions to standard GCC +(flagged below with ``APPLE ONLY''), and that not all generic GCC +options are available or supported on Darwin / Mac OS X. In particular, +Apple does not currently support the compilation of Fortran, Ada, or +Java, although there are third parties who have made these work. +@c APPLE LOCAL end manual + +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), +cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) +and the Info entries for @file{gcc}, @file{cpp}, @file{as}, +@file{ld}, @file{binutils} and @file{gdb}. +@c man end +@c man begin BUGS +@c APPLE LOCAL begin Apple bug-report +To report bugs to Apple, see +@w{@uref{http://developer.apple.com/bugreporter}}. +@c APPLE LOCAL end Apple bug-report +@c man end +@c man begin AUTHOR +See the Info entry for @command{gcc}, or +@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, +for contributors to GCC@. +@c man end +@end ignore + +@node Invoking GCC +@chapter GCC Command Options +@cindex GCC command options +@cindex command options +@cindex options, GCC command + +@c man begin DESCRIPTION +When you invoke GCC, it normally does preprocessing, compilation, +assembly and linking. The ``overall options'' allow you to stop this +process at an intermediate stage. For example, the @option{-c} option +says not to run the linker. Then the output consists of object files +output by the assembler. + +Other options are passed on to one stage of processing. Some options +control the preprocessor and others the compiler itself. Yet other +options control the assembler and linker; most of these are not +documented here, since you rarely need to use any of them. + +@cindex C compilation options +Most of the command line options that you can use with GCC are useful +for C programs; when an option is only useful with another language +(usually C++), the explanation says so explicitly. If the description +for a particular option does not mention a source language, you can use +that option with all supported languages. + +@cindex C++ compilation options +@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special +options for compiling C++ programs. + +@cindex grouping options +@cindex options, grouping +The @command{gcc} program accepts options and file names as operands. Many +options have multi-letter names; therefore multiple single-letter options +may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d +-r}}. + +@cindex order of options +@cindex options, order +You can mix options and other arguments. For the most part, the order +you use doesn't matter. Order does matter when you use several options +of the same kind; for example, if you specify @option{-L} more than once, +the directories are searched in the order specified. + +Many options have long names starting with @samp{-f} or with +@samp{-W}---for example, +@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of +these have both positive and negative forms; the negative form of +@option{-ffoo} would be @option{-fno-foo}. This manual documents +only one of these two forms, whichever one is not the default. + +@c man end + +@xref{Option Index}, for an index to GCC's options. + +@menu +* Option Summary:: Brief list of all options, without explanations. +* Overall Options:: Controlling the kind of output: + an executable, object files, assembler files, + or preprocessed source. +* Invoking G++:: Compiling C++ programs. +* C Dialect Options:: Controlling the variant of C language compiled. +* C++ Dialect Options:: Variations on C++. +* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C + and Objective-C++. +* Language Independent Options:: Controlling how diagnostics should be + formatted. +* Warning Options:: How picky should the compiler be? +* Debugging Options:: Symbol tables, measurements, and debugging dumps. +* Optimize Options:: How much optimization? +* Preprocessor Options:: Controlling header files and macro definitions. + Also, getting dependency information for Make. +* Assembler Options:: Passing options to the assembler. +* Link Options:: Specifying libraries and so on. +* Directory Options:: Where to find header files and libraries. + Where to find the compiler executable files. +* Spec Files:: How to pass switches to sub-processes. +* Target Options:: Running a cross-compiler, or an old version of GCC. +* Submodel Options:: Specifying minor hardware or convention variations, + such as 68010 vs 68020. +* Code Gen Options:: Specifying conventions for function calls, data layout + and register usage. +* Environment Variables:: Env vars that affect GCC. +* Precompiled Headers:: Compiling a header once, and using it many times. +* Running Protoize:: Automatically adding or removing function prototypes. +@end menu + +@c man begin OPTIONS + +@node Option Summary +@section Option Summary + +Here is a summary of all the options, grouped by type. Explanations are +in the following sections. + +@table @emph +@item Overall Options +@xref{Overall Options,,Options Controlling the Kind of Output}. +@gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol +@c APPLE LOCAL -ObjC 2001-08-03 --sts ** +-ObjC (APPLE ONLY) -ObjC++ (APPLE ONLY) @gol +@c APPLE LOCAL begin fat builds +-arch @var{arch} (APPLE ONLY) @gol +-Xarch_@var{arch} @var{option} (APPLE ONLY) @gol +@c APPLE LOCAL end fat builds +@c APPLE LOCAL ss2 +-fsave-repository=@var{file} @gol +-x @var{language} -v -### --help --target-help --version @@@var{file}} + +@item C Language Options +@xref{C Dialect Options,,Options Controlling C Dialect}. +@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol +-aux-info @var{filename} @gol +@c APPLE LOCAL AltiVec +-faltivec (APPLE ONLY) @gol +@c APPLE LOCAL CW asm blocks +-fasm-blocks (APPLE ONLY) @gol +@c APPLE LOCAL blocks 7205047 5811887 +-fno-asm -fno-blocks -fno-builtin -fno-builtin-@var{function} @gol +-fhosted -ffreestanding -fopenmp -fms-extensions @gol +-trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol +@c APPLE LOCAL 5612787 sse4 +-fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol +@c APPLE LOCAL constant cfstrings --mrs +-fconstant-cfstrings (APPLE ONLY) @gol +@c APPLE LOCAL non lvalue assign +-fnon-lvalue-assign (APPLE ONLY) @gol +@c APPLE LOCAL nested functions 4357979 */ +-fno-nested-functions @gol +@c APPLE LOCAL pch distcc --mrs +-fpch-preprocess (APPLE ONLY) @gol +-fsigned-bitfields -fsigned-char @gol +@c APPLE LOCAL -Wno-#warnings +-Wno-#warnings (APPLE ONLY) @gol +@c APPLE LOCAL -Wextra-tokens 2001-08-02 --sts ** +-Wextra-tokens (APPLE ONLY) @gol +@c APPLE LOCAL -Wnewline-eof 2001-08-23 --sts ** +-Wnewline-eof (APPLE ONLY) @gol +@c APPLE LOCAL -Wno-altivec-long-deprecated --ilr ** +-Wno-altivec-long-deprecated (APPLE ONLY) +@c APPLE LOCAL begin 5695218 +-fglobal-alloc-prefer-bytes (APPLE ONLY) +-fno-global-alloc-prefer-bytes (APPLE ONLY) +@c APPLE LOCAL end 5695218 +@c APPLE LOCAL fwritable strings +-funsigned-bitfields -funsigned-char -fwritable-strings} + +@item C++ Language Options +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. +@gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol +-fconserve-space -ffriend-injection @gol +-fno-elide-constructors @gol +-fno-enforce-eh-specs @gol +-ffor-scope -fno-for-scope -fno-gnu-keywords @gol +-fno-implicit-templates @gol +-fno-implicit-inline-templates @gol +-fno-implement-inlines -fms-extensions @gol +-fno-nonansi-builtins -fno-operator-names @gol +-fno-optional-diags -fpermissive @gol +-frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol +-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol +-fno-default-inline -fvisibility-inlines-hidden @gol +@c APPLE LOCAL mainline 2007-06-28 ms tinfo compat 4230099 +-fvisibility-ms-compat +-Wabi -Wctor-dtor-privacy @gol +-Wnon-virtual-dtor -Wreorder @gol +-Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol +-Wno-non-template-friend -Wold-style-cast @gol +-Woverloaded-virtual -Wno-pmf-conversions @gol +-Wsign-promo} + +@item Objective-C and Objective-C++ Language Options +@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling +Objective-C and Objective-C++ Dialects}. +@gccoptlist{-fconstant-string-class=@var{class-name} @gol +-fgnu-runtime -fnext-runtime @gol +-fno-nil-receivers @gol +-fobjc-call-cxx-cdtors @gol +-fobjc-direct-dispatch @gol +@c APPLE LOCAL radar 4512786 +-fobjc-sjlj-exceptions @gol +-fobjc-gc @gol +-freplace-objc-classes @gol +-fzero-link @gol +-gen-decls @gol +-Wassign-intercept @gol +-Wno-protocol -Wselector @gol +@c APPLE LOCAL radar 5172645 +-Wno-property-assign-default @gol +-Wstrict-selector-match @gol +-Wundeclared-selector} + +@item Language Independent Options +@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. +@gccoptlist{-fmessage-length=@var{n} @gol +-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol +-fdiagnostics-show-option} + +@item Warning Options +@xref{Warning Options,,Options to Request or Suppress Warnings}. +@gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol +-w -Wextra -Wall -Waddress -Waggregate-return -Wno-attributes @gol +-Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol +-Wconversion -Wno-deprecated-declarations @gol +-Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol +-Werror -Werror=* -Werror-implicit-function-declaration @gol +@c APPLE LOCAL default to Wformat-security 5764921 +-Wfatal-errors -Wfloat-equal -Wno-format -Wformat=2 @gol +-Wno-format-extra-args -Wformat-nonliteral @gol +@c APPLE LOCAL default to Wformat-security 5764921 +-Wno-format-security -Wformat-y2k @gol +@c APPLE LOCAL Wglobal-constructors 6324584 +-Wglobal-constructors @gol +-Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol +-Wimport -Wno-import -Winit-self -Winline @gol +-Wno-int-to-pointer-cast @gol +-Wno-invalid-offsetof -Winvalid-pch @gol +-Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol +-Wmain -Wmissing-braces -Wmissing-field-initializers @gol +-Wmissing-format-attribute -Wmissing-include-dirs @gol +-Wmissing-noreturn @gol +@c APPLE LOCAL warn missing prototype 6261539 +-Wmissing-prototypes @gol +@c APPLE LOCAL -Wmost +-Wmost (APPLE ONLY) @gol +-Wno-multichar -Wnonnull -Wno-overflow @gol +-Woverlength-strings -Wpacked -Wpadded @gol +-Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol +-Wredundant-decls @gol +-Wreturn-type -Wsequence-point -Wshadow @gol +-Wsign-compare -Wstack-protector @gol +-Wstrict-aliasing -Wstrict-aliasing=2 @gol +-Wstrict-overflow -Wstrict-overflow=@var{n} @gol +-Wswitch -Wswitch-default -Wswitch-enum @gol +-Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol +-Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol +-Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol +-Wunused-value -Wunused-variable -Wvariadic-macros @gol +-Wvolatile-register-var -Wwrite-strings} + +@c APPLE LOCAL begin -Wdiscard-qual 4086969 +@item C-only Warning Options +@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol +@c APPLE LOCAL warn missing prototype 6261539 +-Wnested-externs -Wold-style-definition @gol +-Wstrict-prototypes -Wtraditional @gol +-Wdeclaration-after-statement -Wno-discard-qual -Wno-pointer-sign} +@c APPLE LOCAL end -Wdiscard-qual 4086969 + +@item Debugging Options +@xref{Debugging Options,,Options for Debugging Your Program or GCC}. +@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol +-fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol +-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol +-fdump-ipa-all -fdump-ipa-cgraph @gol +-fdump-tree-all @gol +-fdump-tree-original@r{[}-@var{n}@r{]} @gol +-fdump-tree-optimized@r{[}-@var{n}@r{]} @gol +-fdump-tree-inlined@r{[}-@var{n}@r{]} @gol +-fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol +-fdump-tree-ch @gol +-fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol +-fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol +-fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol +-fdump-tree-dom@r{[}-@var{n}@r{]} @gol +-fdump-tree-dse@r{[}-@var{n}@r{]} @gol +-fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol +-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol +-fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol +-fdump-tree-nrv -fdump-tree-vect @gol +-fdump-tree-sink @gol +-fdump-tree-sra@r{[}-@var{n}@r{]} @gol +-fdump-tree-salias @gol +-fdump-tree-fre@r{[}-@var{n}@r{]} @gol +-fdump-tree-vrp@r{[}-@var{n}@r{]} @gol +-ftree-vectorizer-verbose=@var{n} @gol +-fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol +@c APPLE LOCAL 4167759 +-flimit-debug-info @gol +-feliminate-dwarf2-dups -feliminate-unused-debug-types @gol +-feliminate-unused-debug-symbols -femit-class-debug-always @gol +@c APPLE LOCAL opt diary +-fmem-report -fopt-diary -fprofile-arcs @gol +-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol +-ftest-coverage -ftime-report -fvar-tracking @gol +-g -g@var{level} -gcoff -gdwarf-2 @gol +-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol +-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol +-print-multi-directory -print-multi-lib @gol +-print-prog-name=@var{program} -print-search-dirs -Q @gol +-save-temps -time} + +@item Optimization Options +@xref{Optimize Options,,Options that Control Optimization}. +@gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol +-falign-labels=@var{n} -falign-loops=@var{n} @gol +@c APPLE LOCAL -falign-loops-max-skip +-falign-loops-max-skip=@var{n} -falign-jumps-max-skip=@var{n} @gol +-fbounds-check -fmudflap -fmudflapth -fmudflapir @gol +-fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol +-fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol +@c APPLE LOCAL add fcreate-profile +-fcaller-saves -fcprop-registers -fcreate-profile -fcse-follow-jumps @gol +-fcse-skip-blocks -fcx-limited-range -fdata-sections @gol +-fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol +-fexpensive-optimizations -ffast-math -ffloat-store @gol +-fforce-addr -ffunction-sections @gol +-fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol +-fcrossjumping -fif-conversion -fif-conversion2 @gol +-finline-functions -finline-functions-called-once @gol +-finline-limit=@var{n} -fkeep-inline-functions @gol +@c APPLE LOCAL begin ARM conditionally disable local RA +-fkeep-static-consts @gol +-flocal-alloc (APPLE ONLY) @gol +-fmerge-constants -fmerge-all-constants @gol +@c APPLE LOCAL end ARM conditionally disable local RA +-fmodulo-sched -fno-branch-count-reg @gol +-fno-default-inline -fno-defer-pop -fmove-loop-invariants @gol +-fno-function-cse -fno-guess-branch-probability @gol +-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol +-funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol +-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol +@c APPLE LOCAL 4356747 stack realign +-mstackrealign @gol +-fomit-frame-pointer -foptimize-register-move @gol +-foptimize-sibling-calls -fprefetch-loop-arrays @gol +-fprofile-generate -fprofile-use @gol +-fregmove -frename-registers @gol +-freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol +-frerun-cse-after-loop @gol +-frounding-math -frtl-abstract-sequences @gol +-fschedule-insns -fschedule-insns2 @gol +-fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol +-fsched-spec-load-dangerous @gol +-fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol +-fsched2-use-superblocks @gol +-fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol +-fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol +-fstack-protector -fstack-protector-all @gol +-fstrict-aliasing -fstrict-overflow -ftracer -fthread-jumps @gol +-funroll-all-loops -funroll-loops -fpeel-loops @gol +-fsplit-ivs-in-unroller -funswitch-loops @gol +-fvariable-expansion-in-unroller @gol +-ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol +-ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol +-ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol +-ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol +@c APPLE LOCAL add fuse-profile +-ftree-vect-loop-version -ftree-salias -fuse-profile -fipa-pta -fweb @gol +-ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol +--param @var{name}=@var{value} +@c APPLE LOCAL -fast, -Oz +-O -O0 -O1 -O2 -O3 -Os -Oz (APPLE ONLY) -fast (APPLE ONLY)} + +@item Preprocessor Options +@xref{Preprocessor Options,,Options Controlling the Preprocessor}. +@gccoptlist{-A@var{question}=@var{answer} @gol +-A-@var{question}@r{[}=@var{answer}@r{]} @gol +-C -dD -dI -dM -dN @gol +-D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol +-idirafter @var{dir} @gol +-include @var{file} -imacros @var{file} @gol +-iprefix @var{file} -iwithprefix @var{dir} @gol +-iwithprefixbefore @var{dir} -isystem @var{dir} @gol +-imultilib @var{dir} -isysroot @var{dir} @gol +@c APPLE LOCAL ARM iwithsysroot 4917039 +-iwithsysroot (APPLE ONLY) @var{dir} @gol +-M -MM -MF -MG -MP -MQ -MT -nostdinc @gol +-P -fworking-directory -remap @gol +-trigraphs -undef -U@var{macro} -Wp,@var{option} @gol +-Xpreprocessor @var{option}} + +@item Assembler Option +@xref{Assembler Options,,Passing Options to the Assembler}. +@gccoptlist{-Wa,@var{option} -Xassembler @var{option}} + +@item Linker Options +@xref{Link Options,,Options for Linking}. +@gccoptlist{@var{object-file-name} -l@var{library} @gol +-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol +-s -static -static-libgcc -shared -shared-libgcc -symbolic @gol +-Wl,@var{option} -Xlinker @var{option} @gol +-u @var{symbol}} + +@item Directory Options +@xref{Directory Options,,Options for Directory Search}. +@gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir} +-specs=@var{file} -I- --sysroot=@var{dir}} + +@item Target Options +@c I wrote this xref this way to avoid overfull hbox. -- rms +@xref{Target Options}. +@gccoptlist{-V @var{version} -b @var{machine}} + +@item Machine Dependent Options +@xref{Submodel Options,,Hardware Models and Configurations}. +@c This list is ordered alphanumerically by subsection name. +@c Try and put the significant identifier (CPU or system) first, +@c so users have a clue at guessing where the ones they want will be. + +@c APPLE LOCAL prune man page +@ignore +@emph{ARC Options} +@gccoptlist{-EB -EL @gol +-mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol +-mdata=@var{data-section} -mrodata=@var{readonly-data-section}} +@c APPLE LOCAL ARM prune man page +@end ignore + +@emph{ARM Options} +@gccoptlist{-mapcs-frame -mno-apcs-frame @gol +-mabi=@var{name} @gol +-mapcs-stack-check -mno-apcs-stack-check @gol +-mapcs-float -mno-apcs-float @gol +-mapcs-reentrant -mno-apcs-reentrant @gol +-msched-prolog -mno-sched-prolog @gol +-mlittle-endian -mbig-endian -mwords-little-endian @gol +-mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol +-mthumb-interwork -mno-thumb-interwork @gol +-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol +-mstructure-size-boundary=@var{n} @gol +-mabort-on-noreturn @gol +-mlong-calls -mno-long-calls @gol +-msingle-pic-base -mno-single-pic-base @gol +-mpic-register=@var{reg} @gol +-mnop-fun-dllimport @gol +-mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol +-mpoke-function-name @gol +-mthumb -marm @gol +-mtpcs-frame -mtpcs-leaf-frame @gol +-mcaller-super-interworking -mcallee-super-interworking @gol +@c APPLE LOCAL begin 5946347 ms_struct support +-mtp=@var{name} @gol +-mms-bitfields -mno-ms-bitfields} +@c APPLE LOCAL end 5946347 ms_struct support + +@c APPLE LOCAL ARM prune man page +@ignore +@emph{AVR Options} +@gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol +-mcall-prologues -mno-tablejump -mtiny-stack -mint8} + +@emph{Blackfin Options} +@gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol +-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol +-mlow-64k -mno-low64k -mid-shared-library @gol +-mno-id-shared-library -mshared-library-id=@var{n} @gol +-mlong-calls -mno-long-calls} + +@emph{CRIS Options} +@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol +-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol +-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol +-mstack-align -mdata-align -mconst-align @gol +-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol +-melf -maout -melinux -mlinux -sim -sim2 @gol +-mmul-bug-workaround -mno-mul-bug-workaround} +@c APPLE LOCAL prune man page +@end ignore + +@emph{CRX Options} +@gccoptlist{-mmac -mpush-args} + +@emph{Darwin Options} +@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol +-arch_only -bind_at_load -bundle -bundle_loader @gol +-client_name -compatibility_version -current_version @gol +-dead_strip @gol +-dependency-file -dylib_file -dylinker_install_name @gol +-dynamic -dynamiclib -exported_symbols_list @gol +-filelist -flat_namespace -force_cpusubtype_ALL @gol +@c APPLE LOCAL 7519550 force local +-force_flat_namespace -force_load -headerpad_max_install_names @gol +@c APPLE LOCAL iframework for 4.3 4094959 +-iframework @gol +-image_base -init -install_name -keep_private_externs @gol +-multi_module -multiply_defined -multiply_defined_unused @gol +-noall_load -no_dead_strip_inits_and_terms @gol +-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol +-pagezero_size -prebind -prebind_all_twolevel_modules @gol +-private_bundle -read_only_relocs -sectalign @gol +-sectobjectsymbols -whyload -seg1addr @gol +-sectcreate -sectobjectsymbols -sectorder @gol +-segaddr -segs_read_only_addr -segs_read_write_addr @gol +-seg_addr_table -seg_addr_table_filename -seglinkedit @gol +-segprot -segs_read_only_addr -segs_read_write_addr @gol +-single_module -static -sub_library -sub_umbrella @gol +-twolevel_namespace -umbrella -undefined @gol +-unexported_symbols_list -weak_reference_mismatches @gol +-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol +@c APPLE LOCAL ARM 5905142 +-miphoneos-version-min=@var{version} @gol +@c APPLE LOCAL pascal strings +-mpascal-strings (APPLE ONLY) @gol +@c APPLE LOCAL begin fat builds +-mkernel -mone-byte-bool @gol +-Xarch_@var{arch}} +@c APPLE LOCAL end fat builds + +@c APPLE LOCAL prune man page +@ignore +@emph{DEC Alpha Options} +@gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol +-mieee -mieee-with-inexact -mieee-conformant @gol +-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol +-mtrap-precision=@var{mode} -mbuild-constants @gol +-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol +-mbwx -mmax -mfix -mcix @gol +-mfloat-vax -mfloat-ieee @gol +-mexplicit-relocs -msmall-data -mlarge-data @gol +-msmall-text -mlarge-text @gol +-mmemory-latency=@var{time}} + +@emph{DEC Alpha/VMS Options} +@gccoptlist{-mvms-return-codes} + +@emph{FRV Options} +@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol +-mhard-float -msoft-float @gol +-malloc-cc -mfixed-cc -mdword -mno-dword @gol +-mdouble -mno-double @gol +-mmedia -mno-media -mmuladd -mno-muladd @gol +-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol +-mlinked-fp -mlong-calls -malign-labels @gol +-mlibrary-pic -macc-4 -macc-8 @gol +-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol +-moptimize-membar -mno-optimize-membar @gol +-mscc -mno-scc -mcond-exec -mno-cond-exec @gol +-mvliw-branch -mno-vliw-branch @gol +-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol +-mno-nested-cond-exec -mtomcat-stats @gol +-mTLS -mtls @gol +-mcpu=@var{cpu}} + +@emph{GNU/Linux Options} +@gccoptlist{-muclibc} + +@emph{H8/300 Options} +@gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300} + +@emph{HPPA Options} +@gccoptlist{-march=@var{architecture-type} @gol +-mbig-switch -mdisable-fpregs -mdisable-indexing @gol +-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol +-mfixed-range=@var{register-range} @gol +-mjump-in-delay -mlinker-opt -mlong-calls @gol +-mlong-load-store -mno-big-switch -mno-disable-fpregs @gol +-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol +-mno-jump-in-delay -mno-long-load-store @gol +-mno-portable-runtime -mno-soft-float @gol +-mno-space-regs -msoft-float -mpa-risc-1-0 @gol +-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol +-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol +-munix=@var{unix-std} -nolibdld -static -threads} +@c APPLE LOCAL prune man page +@end ignore + +@emph{i386 and x86-64 Options} +@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol +-mfpmath=@var{unit} @gol +-masm=@var{dialect} -mno-fancy-math-387 @gol +-mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol +-mno-wide-multiply -mrtd -malign-double @gol +-mpreferred-stack-boundary=@var{num} @gol +@c APPLE LOCAL begin 5612787 sse4 +-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -msse4a @gol +@c APPLE LOCAL end 5612787 sse4 +-mthreads -mno-align-stringops -minline-all-stringops @gol +-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol +-m96bit-long-double -mregparm=@var{num} -msseregparm @gol +-mstackrealign @gol +-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol +-mcmodel=@var{code-model} @gol +@c APPLE LOCAL begin 5946347 ms_struct support +-m32 -m64 -mlarge-data-threshold=@var{num} @gol +-mms-bitfields -mno-ms-bitfields} +@c APPLE LOCAL end 5946347 ms_struct support + +@c APPLE LOCAL prune man page +@ignore +@emph{IA-64 Options} +@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol +-mvolatile-asm-stop -mregister-names -mno-sdata @gol +-mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol +-minline-float-divide-max-throughput @gol +-minline-int-divide-min-latency @gol +-minline-int-divide-max-throughput @gol +-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol +-mno-dwarf2-asm -mearly-stop-bits @gol +-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol +-mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol +-mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol +-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol +-msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol +-mno-sched-prefer-non-data-spec-insns @gol +-mno-sched-prefer-non-control-spec-insns @gol +-mno-sched-count-spec-in-critical-path} + +@emph{M32R/D Options} +@gccoptlist{-m32r2 -m32rx -m32r @gol +-mdebug @gol +-malign-loops -mno-align-loops @gol +-missue-rate=@var{number} @gol +-mbranch-cost=@var{number} @gol +-mmodel=@var{code-size-model-type} @gol +-msdata=@var{sdata-type} @gol +-mno-flush-func -mflush-func=@var{name} @gol +-mno-flush-trap -mflush-trap=@var{number} @gol +-G @var{num}} + +@emph{M32C Options} +@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} + +@emph{M680x0 Options} +@gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol +-m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield @gol +-mc68000 -mc68020 @gol +-mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol +-malign-int -mstrict-align -msep-data -mno-sep-data @gol +-mshared-library-id=n -mid-shared-library -mno-id-shared-library} + +@emph{M68hc1x Options} +@gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol +-mauto-incdec -minmax -mlong-calls -mshort @gol +-msoft-reg-count=@var{count}} + +@emph{MCore Options} +@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol +-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol +-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol +-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol +-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} + +@emph{MIPS Options} +@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol +-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol +-mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol +-mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol +-mfp32 -mfp64 -mhard-float -msoft-float @gol +-msingle-float -mdouble-float -mdsp -mpaired-single -mips3d @gol +-mlong64 -mlong32 -msym32 -mno-sym32 @gol +-G@var{num} -membedded-data -mno-embedded-data @gol +-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol +-msplit-addresses -mno-split-addresses @gol +-mexplicit-relocs -mno-explicit-relocs @gol +-mcheck-zero-division -mno-check-zero-division @gol +-mdivide-traps -mdivide-breaks @gol +-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol +-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol +-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol +-mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol +-mfix-sb1 -mno-fix-sb1 @gol +-mflush-func=@var{func} -mno-flush-func @gol +-mbranch-likely -mno-branch-likely @gol +-mfp-exceptions -mno-fp-exceptions @gol +-mvr4130-align -mno-vr4130-align} + +@emph{MMIX Options} +@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol +-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol +-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol +-mno-base-addresses -msingle-exit -mno-single-exit} + +@emph{MN10300 Options} +@gccoptlist{-mmult-bug -mno-mult-bug @gol +-mam33 -mno-am33 @gol +-mam33-2 -mno-am33-2 @gol +-mreturn-pointer-on-d0 @gol +-mno-crt0 -mrelax} + +@emph{MT Options} +@gccoptlist{-mno-crt0 -mbacc -msim @gol +-march=@var{cpu-type} } + +@emph{PDP-11 Options} +@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol +-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol +-mint16 -mno-int32 -mfloat32 -mno-float64 @gol +-mfloat64 -mno-float32 -mabshi -mno-abshi @gol +-mbranch-expensive -mbranch-cheap @gol +-msplit -mno-split -munix-asm -mdec-asm} +@c APPLE LOCAL prune man page +@end ignore + +@emph{PowerPC Options} +See RS/6000 and PowerPC Options. + +@emph{RS/6000 and PowerPC Options} +@gccoptlist{-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mpower -mno-power -mpower2 -mno-power2 @gol +-mpowerpc -mpowerpc64 -mno-powerpc @gol +-maltivec -mno-altivec @gol +@c APPLE LOCAL AltiVec +-mpim-altivec -mno-pim-altivec @gol +-mpowerpc-gpopt -mno-powerpc-gpopt @gol +-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol +-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol +-mnew-mnemonics -mold-mnemonics @gol +-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol +-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol +-malign-power -malign-natural @gol +-msoft-float -mhard-float -mmultiple -mno-multiple @gol +-mstring -mno-string -mupdate -mno-update @gol +-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol +-mstrict-align -mno-strict-align -mrelocatable @gol +-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol +-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol +-mdynamic-no-pic -maltivec -mswdiv @gol +-mprioritize-restricted-insns=@var{priority} @gol +-msched-costly-dep=@var{dependence_type} @gol +-minsert-sched-nops=@var{scheme} @gol +-mcall-sysv -mcall-netbsd @gol +-maix-struct-return -msvr4-struct-return @gol +-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol +-misel -mno-isel @gol +-misel=yes -misel=no @gol +-mspe -mno-spe @gol +-mspe=yes -mspe=no @gol +-mvrsave -mno-vrsave @gol +-mmulhw -mno-mulhw @gol +-mdlmzb -mno-dlmzb @gol +-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol +-mprototype -mno-prototype @gol +-msim -mmvme -mads -myellowknife -memb -msdata @gol +@c APPLE LOCAL begin 5946347 ms_struct support +-msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread @gol +-mms-bitfields -mno-ms-bitfields} +@c APPLE LOCAL end 5946347 ms_struct support + +@c APPLE LOCAL prune man page +@ignore +@emph{S/390 and zSeries Options} +@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol +-mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol +-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol +-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol +-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol +-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol +-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard} + +@emph{Score Options} +@gccoptlist{-meb -mel @gol +-mnhwloop @gol +-muls @gol +-mmac @gol +-mscore5 -mscore5u -mscore7 -mscore7d} + +@emph{SH Options} +@gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol +-m4-nofpu -m4-single-only -m4-single -m4 @gol +-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol +-m5-64media -m5-64media-nofpu @gol +-m5-32media -m5-32media-nofpu @gol +-m5-compact -m5-compact-nofpu @gol +-mb -ml -mdalign -mrelax @gol +-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol +-mieee -misize -mpadstruct -mspace @gol +-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol +-mdivsi3_libfunc=@var{name} @gol +-madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol + -minvalid-symbols} + +@emph{SPARC Options} +@gccoptlist{-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mcmodel=@var{code-model} @gol +-m32 -m64 -mapp-regs -mno-app-regs @gol +-mfaster-structs -mno-faster-structs @gol +-mfpu -mno-fpu -mhard-float -msoft-float @gol +-mhard-quad-float -msoft-quad-float @gol +-mimpure-text -mno-impure-text -mlittle-endian @gol +-mstack-bias -mno-stack-bias @gol +-munaligned-doubles -mno-unaligned-doubles @gol +-mv8plus -mno-v8plus -mvis -mno-vis +-threads -pthreads -pthread} + +@emph{System V Options} +@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} + +@emph{TMS320C3x/C4x Options} +@gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol +-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol +-mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol +-mparallel-insns -mparallel-mpy -mpreserve-float} + +@emph{V850 Options} +@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol +-mprolog-function -mno-prolog-function -mspace @gol +-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol +-mapp-regs -mno-app-regs @gol +-mdisable-callt -mno-disable-callt @gol +-mv850e1 @gol +-mv850e @gol +-mv850 -mbig-switch} + +@emph{VAX Options} +@gccoptlist{-mg -mgnu -munix} + +@emph{x86-64 Options} +See i386 and x86-64 Options. + +@emph{Xstormy16 Options} +@gccoptlist{-msim} + +@emph{Xtensa Options} +@gccoptlist{-mconst16 -mno-const16 @gol +-mfused-madd -mno-fused-madd @gol +-mtext-section-literals -mno-text-section-literals @gol +-mtarget-align -mno-target-align @gol +-mlongcalls -mno-longcalls} + +@emph{zSeries Options} +See S/390 and zSeries Options. +@c APPLE LOCAL prune man page +@end ignore + +@item Code Generation Options +@xref{Code Gen Options,,Options for Code Generation Conventions}. +@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol +-ffixed-@var{reg} -fexceptions @gol +-fnon-call-exceptions -funwind-tables @gol +-fasynchronous-unwind-tables @gol +-finhibit-size-directive -finstrument-functions @gol +-fno-common -fno-ident @gol +-fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol +-fno-jump-tables @gol +-freg-struct-return -fshort-enums @gol +-fshort-double -fshort-wchar @gol +-fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol +-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol +-fargument-alias -fargument-noalias @gol +-fargument-noalias-global -fargument-noalias-anything +-fleading-underscore -ftls-model=@var{model} @gol +@c APPLE LOCAL begin prune man page 5547358 +@c -ftrapv +-fwrapv -fbounds-check @gol +@c APPLE LOCAL end prune man page +-fvisibility} +@end table + +@menu +* Overall Options:: Controlling the kind of output: + an executable, object files, assembler files, + or preprocessed source. +* C Dialect Options:: Controlling the variant of C language compiled. +* C++ Dialect Options:: Variations on C++. +* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C + and Objective-C++. +* Language Independent Options:: Controlling how diagnostics should be + formatted. +* Warning Options:: How picky should the compiler be? +* Debugging Options:: Symbol tables, measurements, and debugging dumps. +* Optimize Options:: How much optimization? +* Preprocessor Options:: Controlling header files and macro definitions. + Also, getting dependency information for Make. +* Assembler Options:: Passing options to the assembler. +* Link Options:: Specifying libraries and so on. +* Directory Options:: Where to find header files and libraries. + Where to find the compiler executable files. +* Spec Files:: How to pass switches to sub-processes. +* Target Options:: Running a cross-compiler, or an old version of GCC. +@end menu + +@node Overall Options +@section Options Controlling the Kind of Output + +Compilation can involve up to four stages: preprocessing, compilation +proper, assembly and linking, always in that order. GCC is capable of +preprocessing and compiling several files either into several +assembler input files, or into one assembler input file; then each +assembler input file produces an object file, and linking combines all +the object files (those newly compiled, and those specified as input) +into an executable file. + +@cindex file name suffix +For any given input file, the file name suffix determines what kind of +compilation is done: + +@table @gcctabopt +@item @var{file}.c +C source code which must be preprocessed. + +@item @var{file}.i +C source code which should not be preprocessed. + +@item @var{file}.ii +C++ source code which should not be preprocessed. + +@item @var{file}.m +Objective-C source code. Note that you must link with the @file{libobjc} +library to make an Objective-C program work. + +@item @var{file}.mi +Objective-C source code which should not be preprocessed. + +@item @var{file}.mm +@itemx @var{file}.M +Objective-C++ source code. Note that you must link with the @file{libobjc} +library to make an Objective-C++ program work. Note that @samp{.M} refers +to a literal capital M@. + +@item @var{file}.mii +Objective-C++ source code which should not be preprocessed. + +@item @var{file}.h +C, C++, Objective-C or Objective-C++ header file to be turned into a +precompiled header. + +@item @var{file}.cc +@itemx @var{file}.cp +@itemx @var{file}.cxx +@itemx @var{file}.cpp +@itemx @var{file}.CPP +@itemx @var{file}.c++ +@itemx @var{file}.C +C++ source code which must be preprocessed. Note that in @samp{.cxx}, +the last two letters must both be literally @samp{x}. Likewise, +@samp{.C} refers to a literal capital C@. + +@c APPLE LOCAL begin Objective-C++ +@c Delete duplicate @var{file}.mm, @var{file}.M, @var{file}.mii. +@c APPLE LOCAL end Objective-C++ + +@item @var{file}.hh +@itemx @var{file}.H +C++ header file to be turned into a precompiled header. + +@item @var{file}.f +@itemx @var{file}.for +@itemx @var{file}.FOR +Fixed form Fortran source code which should not be preprocessed. + +@item @var{file}.F +@itemx @var{file}.fpp +@itemx @var{file}.FPP +Fixed form Fortran source code which must be preprocessed (with the traditional +preprocessor). + +@item @var{file}.f90 +@itemx @var{file}.f95 +Free form Fortran source code which should not be preprocessed. + +@item @var{file}.F90 +@itemx @var{file}.F95 +Free form Fortran source code which must be preprocessed (with the +traditional preprocessor). + +@c FIXME: Descriptions of Java file types. +@c @var{file}.java +@c @var{file}.class +@c @var{file}.zip +@c @var{file}.jar + +@item @var{file}.ads +Ada source code file which contains a library unit declaration (a +declaration of a package, subprogram, or generic, or a generic +instantiation), or a library unit renaming declaration (a package, +generic, or subprogram renaming declaration). Such files are also +called @dfn{specs}. + +@itemx @var{file}.adb +Ada source code file containing a library unit body (a subprogram or +package body). Such files are also called @dfn{bodies}. + +@c GCC also knows about some suffixes for languages not yet included: +@c Pascal: +@c @var{file}.p +@c @var{file}.pas +@c Ratfor: +@c @var{file}.r + +@item @var{file}.s +@c APPLE LOCAL begin preprocess .s files +Assembler code. Apple's version of GCC runs the preprocessor +on these files as well as those ending in @samp{.S}. +@c APPLE LOCAL end preprocess .s files + +@item @var{file}.S +Assembler code which must be preprocessed. + +@item @var{other} +An object file to be fed straight into linking. +Any file name with no recognized suffix is treated this way. +@end table + +@opindex x +You can specify the input language explicitly with the @option{-x} option: + +@table @gcctabopt +@item -x @var{language} +Specify explicitly the @var{language} for the following input files +(rather than letting the compiler choose a default based on the file +name suffix). This option applies to all following input files until +the next @option{-x} option. Possible values for @var{language} are: +@smallexample +c c-header c-cpp-output +c++ c++-header c++-cpp-output +objective-c objective-c-header objective-c-cpp-output +objective-c++ objective-c++-header objective-c++-cpp-output +assembler assembler-with-cpp +ada +f95 f95-cpp-input +java +treelang +@end smallexample + +@item -x none +Turn off any specification of a language, so that subsequent files are +handled according to their file name suffixes (as they are if @option{-x} +has not been used at all). + +@c APPLE LOCAL begin -ObjC 2001-08-03 --sts ** +@item -ObjC +@itemx -ObjC++ +@opindex ObjC +@opindex ObjC++ +These are similar in effect to @option{-x objective-c} and @option{-x +objective-c++}, but affect only the choice of compiler for files already +identified as source files. (APPLE ONLY) +@c APPLE LOCAL end -ObjC 2001-08-03 --sts ** + +@c APPLE LOCAL begin fat builds +@item -arch @var{arch} +@opindex arch +Compile for the specified target architecture @var{arch}. The +allowable values are @samp{i386}, @samp{x86_64}, @samp{ppc} and +@samp{ppc64}. Multiple options work, and direct the compiler to +produce ``universal'' binaries including object code for each +architecture specified with @option{-arch}. This option only works if +assembler and libraries are available for each architecture specified. +(APPLE ONLY) + +@item -Xarch_@var{arch} @var{option} +@opindex Xarch +Apply @var{option} to the command line for architecture @var{arch}. +This is useful for specifying an option that should only apply to +one architecture when building a ``universal'' binary. (APPLE ONLY) +@c APPLE LOCAL end fat builds + +@c APPLE LOCAL begin ss2 +@item -fsave-repository=@var{file} +@opindex fsave-repository +Save debug info in separate object file. +This is available only while building PCH in -gfull mode. +@c APPLE LOCAL end ss2 + +@item -pass-exit-codes +@opindex pass-exit-codes +Normally the @command{gcc} program will exit with the code of 1 if any +phase of the compiler returns a non-success return code. If you specify +@option{-pass-exit-codes}, the @command{gcc} program will instead return with +numerically highest error produced by any phase that returned an error +indication. The C, C++, and Fortran frontends return 4, if an internal +compiler error is encountered. +@end table + +If you only want some of the stages of compilation, you can use +@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and +one of the options @option{-c}, @option{-S}, or @option{-E} to say where +@command{gcc} is to stop. Note that some combinations (for example, +@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. + +@table @gcctabopt +@item -c +@opindex c +Compile or assemble the source files, but do not link. The linking +stage simply is not done. The ultimate output is in the form of an +object file for each source file. + +By default, the object file name for a source file is made by replacing +the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. + +Unrecognized input files, not requiring compilation or assembly, are +ignored. + +@item -S +@opindex S +Stop after the stage of compilation proper; do not assemble. The output +is in the form of an assembler code file for each non-assembler input +file specified. + +By default, the assembler file name for a source file is made by +replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. + +Input files that don't require compilation are ignored. + +@item -E +@opindex E +Stop after the preprocessing stage; do not run the compiler proper. The +output is in the form of preprocessed source code, which is sent to the +standard output. + +Input files which don't require preprocessing are ignored. + +@cindex output file option +@item -o @var{file} +@opindex o +Place output in file @var{file}. This applies regardless to whatever +sort of output is being produced, whether it be an executable file, +an object file, an assembler file or preprocessed C code. + +If @option{-o} is not specified, the default is to put an executable +file in @file{a.out}, the object file for +@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its +assembler file in @file{@var{source}.s}, a precompiled header file in +@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on +standard output. + +@item -v +@opindex v +Print (on standard error output) the commands executed to run the stages +of compilation. Also print the version number of the compiler driver +program and of the preprocessor and the compiler proper. + +@item -### +@opindex ### +Like @option{-v} except the commands are not executed and all command +arguments are quoted. This is useful for shell scripts to capture the +driver-generated command lines. + +@item -pipe +@opindex pipe +Use pipes rather than temporary files for communication between the +various stages of compilation. This fails to work on some systems where +the assembler is unable to read from a pipe; but the GNU assembler has +no trouble. + +@item -combine +@opindex combine +If you are compiling multiple source files, this option tells the driver +to pass all the source files to the compiler at once (for those +languages for which the compiler can handle this). This will allow +intermodule analysis (IMA) to be performed by the compiler. Currently the only +language for which this is supported is C@. If you pass source files for +multiple languages to the driver, using this option, the driver will invoke +the compiler(s) that support IMA once each, passing each compiler all the +source files appropriate for it. For those languages that do not support +IMA this option will be ignored, and the compiler will be invoked once for +each source file in that language. If you use this option in conjunction +with @option{-save-temps}, the compiler will generate multiple +pre-processed files +(one for each source file), but only one (combined) @file{.o} or +@file{.s} file. + +@item --help +@opindex help +Print (on the standard output) a description of the command line options +understood by @command{gcc}. If the @option{-v} option is also specified +then @option{--help} will also be passed on to the various processes +invoked by @command{gcc}, so that they can display the command line options +they accept. If the @option{-Wextra} option is also specified then command +line options which have no documentation associated with them will also +be displayed. + +@item --target-help +@opindex target-help +Print (on the standard output) a description of target specific command +line options for each tool. + +@item --version +@opindex version +Display the version number and copyrights of the invoked GCC@. + +@include @value{srcdir}/../libiberty/at-file.texi +@end table + +@node Invoking G++ +@section Compiling C++ Programs + +@cindex suffixes for C++ source +@cindex C++ source file suffixes +C++ source files conventionally use one of the suffixes @samp{.C}, +@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or +@samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and +preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes +files with these names and compiles them as C++ programs even if you +call the compiler the same way as for compiling C programs (usually +with the name @command{gcc}). + +@findex g++ +@findex c++ +However, the use of @command{gcc} does not add the C++ library. +@command{g++} is a program that calls GCC and treats @samp{.c}, +@samp{.h} and @samp{.i} files as C++ source files instead of C source +files unless @option{-x} is used, and automatically specifies linking +against the C++ library. This program is also useful when +precompiling a C header file with a @samp{.h} extension for use in C++ +compilations. On many systems, @command{g++} is also installed with +the name @command{c++}. + +@cindex invoking @command{g++} +When you compile C++ programs, you may specify many of the same +command-line options that you use for compiling programs in any +language; or command-line options meaningful for C and related +languages; or options that are meaningful only for C++ programs. +@xref{C Dialect Options,,Options Controlling C Dialect}, for +explanations of options for languages related to C@. +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for +explanations of options that are meaningful only for C++ programs. + +@node C Dialect Options +@section Options Controlling C Dialect +@cindex dialect options +@cindex language dialect options +@cindex options, dialect + +The following options control the dialect of C (or languages derived +from C, such as C++, Objective-C and Objective-C++) that the compiler +accepts: + +@table @gcctabopt +@cindex ANSI support +@cindex ISO support +@item -ansi +@opindex ansi +In C mode, support all ISO C90 programs. In C++ mode, +remove GNU extensions that conflict with ISO C++. + +This turns off certain features of GCC that are incompatible with ISO +C90 (when compiling C code), or of standard C++ (when compiling C++ code), +such as the @code{asm} and @code{typeof} keywords, and +predefined macros such as @code{unix} and @code{vax} that identify the +type of system you are using. It also enables the undesirable and +rarely used ISO trigraph feature. For the C compiler, +it disables recognition of C++ style @samp{//} comments as well as +the @code{inline} keyword. + +The alternate keywords @code{__asm__}, @code{__extension__}, +@code{__inline__} and @code{__typeof__} continue to work despite +@option{-ansi}. You would not want to use them in an ISO C program, of +course, but it is useful to put them in header files that might be included +in compilations done with @option{-ansi}. Alternate predefined macros +such as @code{__unix__} and @code{__vax__} are also available, with or +without @option{-ansi}. + +The @option{-ansi} option does not cause non-ISO programs to be +rejected gratuitously. For that, @option{-pedantic} is required in +addition to @option{-ansi}. @xref{Warning Options}. + +The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} +option is used. Some header files may notice this macro and refrain +from declaring certain functions or defining certain macros that the +ISO standard doesn't call for; this is to avoid interfering with any +programs that might use these names for other things. + +Functions which would normally be built in but do not have semantics +defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in +functions with @option{-ansi} is used. @xref{Other Builtins,,Other +built-in functions provided by GCC}, for details of the functions +affected. + +@item -std= +@opindex std +Determine the language standard. This option is currently only +supported when compiling C or C++. A value for this option must be +provided; possible values are + +@table @samp +@item c89 +@itemx iso9899:1990 +ISO C90 (same as @option{-ansi}). + +@item iso9899:199409 +ISO C90 as modified in amendment 1. + +@item c99 +@itemx c9x +@itemx iso9899:1999 +@itemx iso9899:199x +ISO C99. Note that this standard is not yet fully supported; see +@w{@uref{http://gcc.gnu.org/gcc-4.2/c99status.html}} for more information. The +names @samp{c9x} and @samp{iso9899:199x} are deprecated. + +@item gnu89 +Default, ISO C90 plus GNU extensions (including some C99 features). + +@item gnu99 +@itemx gnu9x +ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC, +this will become the default. The name @samp{gnu9x} is deprecated. + +@item c++98 +The 1998 ISO C++ standard plus amendments. + +@item gnu++98 +The same as @option{-std=c++98} plus GNU extensions. This is the +default for C++ code. +@end table + +Even when this option is not specified, you can still use some of the +features of newer standards in so far as they do not conflict with +previous C standards. For example, you may use @code{__restrict__} even +when @option{-std=c99} is not specified. + +The @option{-std} options specifying some version of ISO C have the same +effects as @option{-ansi}, except that features that were not in ISO C90 +but are in the specified version (for example, @samp{//} comments and +the @code{inline} keyword in ISO C99) are not disabled. + +@xref{Standards,,Language Standards Supported by GCC}, for details of +these standard versions. + +@item -fgnu89-inline +@opindex fgnu89-inline +The option @option{-fgnu89-inline} tells GCC to use the traditional +GNU semantics for @code{inline} functions when in C99 mode. +@xref{Inline,,An Inline Function is As Fast As a Macro}. Using this +option is roughly equivalent to adding the @code{gnu_inline} function +attribute to all inline functions (@pxref{Function Attributes}). + +This option is accepted by GCC versions 4.1.3 and up. In GCC versions +/* APPLE LOCAL extern inline */ +prior to 4.3 (4.2 for Apple's gcc), C99 inline semantics are not supported, and thus this +option is effectively assumed to be present regardless of whether or not +it is specified; the only effect of specifying it explicitly is to +disable warnings about using inline functions in C99 mode. Likewise, +the option @option{-fno-gnu89-inline} is not supported in versions of +/* APPLE LOCAL extern inline */ +GCC before 4.3 (4.2 for Apple's gcc). It is supported only in C99 or gnu99 mode, not in +C89 or gnu89 mode. + +The preprocesor macros @code{__GNUC_GNU_INLINE__} and +@code{__GNUC_STDC_INLINE__} may be used to check which semantics are +in effect for @code{inline} functions. @xref{Common Predefined +Macros,,,cpp,The C Preprocessor}. + +@item -aux-info @var{filename} +@opindex aux-info +Output to the given filename prototyped declarations for all functions +declared and/or defined in a translation unit, including those in header +files. This option is silently ignored in any language other than C@. + +Besides declarations, the file indicates, in comments, the origin of +each declaration (source file and line), whether the declaration was +implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or +@samp{O} for old, respectively, in the first character after the line +number and the colon), and whether it came from a declaration or a +definition (@samp{C} or @samp{F}, respectively, in the following +character). In the case of function definitions, a K&R-style list of +arguments followed by their declarations is also provided, inside +comments, after the declaration. + +@c APPLE LOCAL begin AltiVec +@item -faltivec +This flag is provided for compatibility with Metrowerks CodeWarrior and MrC +compilers as well as previous Apple versions of GCC. It causes the +@option{-mpim-altivec} option to be turned on. +@c APPLE LOCAL end AltiVec + +@c APPLE LOCAL begin CW asm blocks +@item -fasm-blocks +Enable the use of blocks and entire functions of assembly code within +a C or C++ file. The syntax follows that used in CodeWarrior. This +option is not supported for ARM targets. (APPLE ONLY) +@c APPLE LOCAL end CW asm blocks + +@item -fno-asm +@opindex fno-asm +Do not recognize @code{asm}, @code{inline} or @code{typeof} as a +keyword, so that code can use these words as identifiers. You can use +the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} +instead. @option{-ansi} implies @option{-fno-asm}. + +In C++, this switch only affects the @code{typeof} keyword, since +@code{asm} and @code{inline} are standard keywords. You may want to +use the @option{-fno-gnu-keywords} flag instead, which has the same +effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this +switch only affects the @code{asm} and @code{typeof} keywords, since +@code{inline} is a standard keyword in ISO C99. + +@c APPLE LOCAL begin blocks 7205047 5811887 +@item -fno-blocks +@opindex fno-blocks +Disable the use of blocks. In @option{-std=c99} mode, blocks are +turned off by default. @option{-fblocks} can be used to re-enable the +feature, if off. Runtime support for blocks first appeared in Mac OS +X 10.6. When targeting 10.6 (see @option{-mmacosx-version-min}) and +later, the extension is on by default. +@c APPLE LOCAL end blocks 7205047 5811887 + +@item -fno-builtin +@itemx -fno-builtin-@var{function} +@opindex fno-builtin +@cindex built-in functions +Don't recognize built-in functions that do not begin with +@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in +functions provided by GCC}, for details of the functions affected, +including those which are not built-in functions when @option{-ansi} or +@option{-std} options for strict ISO C conformance are used because they +do not have an ISO standard meaning. + +GCC normally generates special code to handle certain built-in functions +more efficiently; for instance, calls to @code{alloca} may become single +instructions that adjust the stack directly, and calls to @code{memcpy} +may become inline copy loops. The resulting code is often both smaller +and faster, but since the function calls no longer appear as such, you +cannot set a breakpoint on those calls, nor can you change the behavior +of the functions by linking with a different library. In addition, +when a function is recognized as a built-in function, GCC may use +information about that function to warn about problems with calls to +that function, or to generate more efficient code, even if the +resulting code still contains calls to that function. For example, +warnings are given with @option{-Wformat} for bad calls to +@code{printf}, when @code{printf} is built in, and @code{strlen} is +known not to modify global memory. + +With the @option{-fno-builtin-@var{function}} option +only the built-in function @var{function} is +disabled. @var{function} must not begin with @samp{__builtin_}. If a +function is named this is not built-in in this version of GCC, this +option is ignored. There is no corresponding +@option{-fbuiltin-@var{function}} option; if you wish to enable +built-in functions selectively when using @option{-fno-builtin} or +@option{-ffreestanding}, you may define macros such as: + +@smallexample +#define abs(n) __builtin_abs ((n)) +#define strcpy(d, s) __builtin_strcpy ((d), (s)) +@end smallexample + +@item -fhosted +@opindex fhosted +@cindex hosted environment + +Assert that compilation takes place in a hosted environment. This implies +@option{-fbuiltin}. A hosted environment is one in which the +entire standard library is available, and in which @code{main} has a return +type of @code{int}. Examples are nearly everything except a kernel. +This is equivalent to @option{-fno-freestanding}. + +@item -ffreestanding +@opindex ffreestanding +@cindex hosted environment + +Assert that compilation takes place in a freestanding environment. This +implies @option{-fno-builtin}. A freestanding environment +is one in which the standard library may not exist, and program startup may +not necessarily be at @code{main}. The most obvious example is an OS kernel. +This is equivalent to @option{-fno-hosted}. + +@xref{Standards,,Language Standards Supported by GCC}, for details of +freestanding and hosted environments. + +@item -fopenmp +@opindex fopenmp +@cindex openmp parallel +Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and +@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the +compiler generates parallel code according to the OpenMP Application +Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. + +@item -fms-extensions +@opindex fms-extensions +Accept some non-standard constructs used in Microsoft header files. + +Some cases of unnamed fields in structures and unions are only +accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union +fields within structs/unions}, for details. + +@item -trigraphs +@opindex trigraphs +Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} +options for strict ISO C conformance) implies @option{-trigraphs}. + +@item -no-integrated-cpp +@opindex no-integrated-cpp +Performs a compilation in two passes: preprocessing and compiling. This +option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the +@option{-B} option. The user supplied compilation step can then add in +an additional preprocessing step after normal preprocessing but before +compiling. The default is to use the integrated cpp (internal cpp) + +The semantics of this option will change if "cc1", "cc1plus", and +"cc1obj" are merged. + +@cindex traditional C language +@cindex C language, traditional +@item -traditional +@itemx -traditional-cpp +@opindex traditional-cpp +@opindex traditional +Formerly, these options caused GCC to attempt to emulate a pre-standard +C compiler. They are now only supported with the @option{-E} switch. +The preprocessor continues to support a pre-standard mode. See the GNU +CPP manual for details. + +@item -fcond-mismatch +@opindex fcond-mismatch +Allow conditional expressions with mismatched types in the second and +third arguments. The value of such an expression is void. This option +is not supported for C++. + +@c APPLE LOCAL begin nested functions 4357979 +@item -fno-nested-functions +@opindex fno-nested-functions +Disable nested functions. This option is not supported for C++ or +Objective-C++. On Darwin, nested functions are disabled by default. +@c APPLE LOCAL end nested functions 4357979 + +@c APPLE LOCAL begin pch distcc --mrs +@item -fpch-preprocess +@opindex fpch-preprocess +Enable PCH processing even when @option{-E} or @option{-save-temps} is used. +@c APPLE LOCAL end pch distcc --mrs + +@c APPLE LOCAL begin non lvalue assign +@item -fnon-lvalue-assign +@opindex fnon-lvalue-assign +C and C++ forbid the use of casts and conditional expressions as lvalues, e.g.: + +@smallexample +float *p, q, r; +((int *)p)++; +(cond ? q : r) = 3.0; +@end smallexample + +@noindent +As a transitional measure, the Apple version of GCC 4.0 allows casts and +conditional expressions to be used as lvalues in certain situations. This +is accomplished via the @option{-fnon-lvalue-assign} switch, which is on +by default. Whenever an lvalue cast or an lvalue conditional expression is +encountered, the compiler will issue a deprecation warning and then rewrite +the expression as follows: + +@smallexample +(type)expr ---becomes---> *(type *)&expr +cond ? expr1 : expr2 ---becomes---> *(cond ? &expr1 : &expr2) +@end smallexample + +To disallow lvalue casts and lvalue conditional expressions altogether, +specify @option{-fno-non-lvalue-assign}; lvalue casts and lvalue conditional +expressions will be disallowed in future versions of Apple's GCC. +@c APPLE LOCAL end non lvalue assign + +@c APPLE LOCAL begin 5612787 sse4 +@item -flax-vector-conversions +@opindex flax-vector-conversions +Allow implicit conversions between vectors with differing numbers of +elements and/or incompatible element types. This option should not be +used for new code. +@c APPLE LOCAL end 5612787 sse4 + +@item -funsigned-char +@opindex funsigned-char +Let the type @code{char} be unsigned, like @code{unsigned char}. + +Each kind of machine has a default for what @code{char} should +be. It is either like @code{unsigned char} by default or like +@code{signed char} by default. + +Ideally, a portable program should always use @code{signed char} or +@code{unsigned char} when it depends on the signedness of an object. +But many programs have been written to use plain @code{char} and +expect it to be signed, or expect it to be unsigned, depending on the +machines they were written for. This option, and its inverse, let you +make such a program work with the opposite default. + +The type @code{char} is always a distinct type from each of +@code{signed char} or @code{unsigned char}, even though its behavior +is always just like one of those two. + +@item -fsigned-char +@opindex fsigned-char +Let the type @code{char} be signed, like @code{signed char}. + +Note that this is equivalent to @option{-fno-unsigned-char}, which is +the negative form of @option{-funsigned-char}. Likewise, the option +@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. + +@item -fsigned-bitfields +@itemx -funsigned-bitfields +@itemx -fno-signed-bitfields +@itemx -fno-unsigned-bitfields +@opindex fsigned-bitfields +@opindex funsigned-bitfields +@opindex fno-signed-bitfields +@opindex fno-unsigned-bitfields +These options control whether a bit-field is signed or unsigned, when the +declaration does not use either @code{signed} or @code{unsigned}. By +default, such a bit-field is signed, because this is consistent: the +basic integer types such as @code{int} are signed types. + +@c APPLE LOCAL begin constant cfstrings +@item -fconstant-cfstrings +@opindex fconstant-cfstrings +Enable the automatic creation of a CoreFoundation-type constant string +whenever a special builtin @code{__builtin__CFStringMakeConstantString} +is called on a literal string. (APPLE ONLY) +@c APPLE LOCAL end constant cfstrings + +@c APPLE LOCAL begin radar 3506309 +@item -Wnonportable-cfstrings +@opindex Wnonportable-cfstrings +Warn if constant CFString objects contain non-portable characters +(default behavior) +@c APPLE LOCAL end radar 3506309 + +@c APPLE LOCAL begin 5695218 +@item -fglobal-alloc-prefer-bytes +@item -fno-global-alloc-prefer-bytes +@opindex fglobal-alloc-prefer-bytes +For the x86_32 architecture, prefer byte or short values to word +values during global register allocation. Some of the registers on +this target can't be used with values smaller than a 32-bit word; +allocating these values earlier increases the chance they will get a +byte-capable (or short-capable) register. Ignored for other targets. +Defaults on with global register allocation (@code{-Os}, @code{-O2}, +or @code{-O3}). (APPLE ONLY) +@c APPLE LOCAL end 5695218 +@c APPLE LOCAL begin fwritable strings. +@item -fwritable-strings +@opindex fwritable-strings +Store string constants in the writable data segment and don't uniquize +them. This is for compatibility with old programs which assume they can +write into string constants. + +Writing into string constants is a very bad idea; ``constants'' should +be constant. + +This option is deprecated. +@c APPLE LOCAL end fwritable strings. +@end table + +@node C++ Dialect Options +@section Options Controlling C++ Dialect + +@cindex compiler options, C++ +@cindex C++ options, command line +@cindex options, C++ +This section describes the command-line options that are only meaningful +for C++ programs; but you can also use most of the GNU compiler options +regardless of what language your program is in. For example, you +might compile a file @code{firstClass.C} like this: + +@smallexample +g++ -g -frepo -O -c firstClass.C +@end smallexample + +@noindent +In this example, only @option{-frepo} is an option meant +only for C++ programs; you can use the other options with any +language supported by GCC@. + +Here is a list of options that are @emph{only} for compiling C++ programs: + +@table @gcctabopt + +@item -fabi-version=@var{n} +@opindex fabi-version +Use version @var{n} of the C++ ABI@. Version 2 is the version of the +C++ ABI that first appeared in G++ 3.4. Version 1 is the version of +the C++ ABI that first appeared in G++ 3.2. Version 0 will always be +the version that conforms most closely to the C++ ABI specification. +Therefore, the ABI obtained using version 0 will change as ABI bugs +are fixed. + +The default is version 2. + +@item -fno-access-control +@opindex fno-access-control +Turn off all access checking. This switch is mainly useful for working +around bugs in the access control code. + +@item -fcheck-new +@opindex fcheck-new +Check that the pointer returned by @code{operator new} is non-null +before attempting to modify the storage allocated. This check is +normally unnecessary because the C++ standard specifies that +@code{operator new} will only return @code{0} if it is declared +@samp{throw()}, in which case the compiler will always check the +return value even without this option. In all other cases, when +@code{operator new} has a non-empty exception specification, memory +exhaustion is signalled by throwing @code{std::bad_alloc}. See also +@samp{new (nothrow)}. + +@item -fconserve-space +@opindex fconserve-space +Put uninitialized or runtime-initialized global variables into the +common segment, as C does. This saves space in the executable at the +cost of not diagnosing duplicate definitions. If you compile with this +flag and your program mysteriously crashes after @code{main()} has +completed, you may have an object that is being destroyed twice because +two definitions were merged. + +This option is no longer useful on most targets, now that support has +been added for putting variables into BSS without making them common. + +@item -ffriend-injection +@opindex ffriend-injection +Inject friend functions into the enclosing namespace, so that they are +visible outside the scope of the class in which they are declared. +Friend functions were documented to work this way in the old Annotated +C++ Reference Manual, and versions of G++ before 4.1 always worked +that way. However, in ISO C++ a friend function which is not declared +in an enclosing scope can only be found using argument dependent +lookup. This option causes friends to be injected as they were in +earlier releases. + +This option is for compatibility, and may be removed in a future +release of G++. + +@item -fno-elide-constructors +@opindex fno-elide-constructors +The C++ standard allows an implementation to omit creating a temporary +which is only used to initialize another object of the same type. +Specifying this option disables that optimization, and forces G++ to +call the copy constructor in all cases. + +@item -fno-enforce-eh-specs +@opindex fno-enforce-eh-specs +Don't generate code to check for violation of exception specifications +at runtime. This option violates the C++ standard, but may be useful +for reducing code size in production builds, much like defining +@samp{NDEBUG}. This does not give user code permission to throw +exceptions in violation of the exception specifications; the compiler +will still optimize based on the specifications, so throwing an +unexpected exception will result in undefined behavior. + +@item -ffor-scope +@itemx -fno-for-scope +@opindex ffor-scope +@opindex fno-for-scope +If @option{-ffor-scope} is specified, the scope of variables declared in +a @i{for-init-statement} is limited to the @samp{for} loop itself, +as specified by the C++ standard. +If @option{-fno-for-scope} is specified, the scope of variables declared in +a @i{for-init-statement} extends to the end of the enclosing scope, +as was the case in old versions of G++, and other (traditional) +implementations of C++. + +The default if neither flag is given to follow the standard, +but to allow and give a warning for old-style code that would +otherwise be invalid, or have different behavior. + +@item -fno-gnu-keywords +@opindex fno-gnu-keywords +Do not recognize @code{typeof} as a keyword, so that code can use this +word as an identifier. You can use the keyword @code{__typeof__} instead. +@option{-ansi} implies @option{-fno-gnu-keywords}. + +@item -fno-implicit-templates +@opindex fno-implicit-templates +Never emit code for non-inline templates which are instantiated +implicitly (i.e.@: by use); only emit code for explicit instantiations. +@xref{Template Instantiation}, for more information. + +@item -fno-implicit-inline-templates +@opindex fno-implicit-inline-templates +Don't emit code for implicit instantiations of inline templates, either. +The default is to handle inlines differently so that compiles with and +without optimization will need the same set of explicit instantiations. + +@item -fno-implement-inlines +@opindex fno-implement-inlines +To save space, do not emit out-of-line copies of inline functions +controlled by @samp{#pragma implementation}. This will cause linker +errors if these functions are not inlined everywhere they are called. + +@item -fms-extensions +@opindex fms-extensions +Disable pedantic warnings about constructs used in MFC, such as implicit +int and getting a pointer to member function via non-standard syntax. + +@item -fno-nonansi-builtins +@opindex fno-nonansi-builtins +Disable built-in declarations of functions that are not mandated by +ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, +@code{index}, @code{bzero}, @code{conjf}, and other related functions. + +@item -fno-operator-names +@opindex fno-operator-names +Do not treat the operator name keywords @code{and}, @code{bitand}, +@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as +synonyms as keywords. + +@item -fno-optional-diags +@opindex fno-optional-diags +Disable diagnostics that the standard says a compiler does not need to +issue. Currently, the only such diagnostic issued by G++ is the one for +a name having multiple meanings within a class. + +@item -fpermissive +@opindex fpermissive +Downgrade some diagnostics about nonconformant code from errors to +warnings. Thus, using @option{-fpermissive} will allow some +nonconforming code to compile. + +@item -frepo +@opindex frepo +Enable automatic template instantiation at link time. This option also +implies @option{-fno-implicit-templates}. @xref{Template +Instantiation}, for more information. + +@item -fno-rtti +@opindex fno-rtti +Disable generation of information about every class with virtual +functions for use by the C++ runtime type identification features +(@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts +of the language, you can save some space by using this flag. Note that +exception handling uses the same information, but it will generate it as +needed. The @samp{dynamic_cast} operator can still be used for casts that +do not require runtime type information, i.e. casts to @code{void *} or to +unambiguous base classes. + +@item -fstats +@opindex fstats +Emit statistics about front-end processing at the end of the compilation. +This information is generally only useful to the G++ development team. + +@item -ftemplate-depth-@var{n} +@opindex ftemplate-depth +Set the maximum instantiation depth for template classes to @var{n}. +A limit on the template instantiation depth is needed to detect +endless recursions during template class instantiation. ANSI/ISO C++ +conforming programs must not rely on a maximum depth greater than 17. + +@item -fno-threadsafe-statics +@opindex fno-threadsafe-statics +Do not emit the extra code to use the routines specified in the C++ +ABI for thread-safe initialization of local statics. You can use this +option to reduce code size slightly in code that doesn't need to be +thread-safe. + +@item -fuse-cxa-atexit +@opindex fuse-cxa-atexit +Register destructors for objects with static storage duration with the +@code{__cxa_atexit} function rather than the @code{atexit} function. +This option is required for fully standards-compliant handling of static +destructors, but will only work if your C library supports +@code{__cxa_atexit}. + +@item -fno-use-cxa-get-exception-ptr +@opindex fno-use-cxa-get-exception-ptr +Don't use the @code{__cxa_get_exception_ptr} runtime routine. This +will cause @code{std::uncaught_exception} to be incorrect, but is necessary +if the runtime routine is not available. + +@item -fvisibility-inlines-hidden +@opindex fvisibility-inlines-hidden +This switch declares that the user does not attempt to compare +pointers to inline methods where the addresses of the two functions +were taken in different shared objects. + +The effect of this is that GCC may, effectively, mark inline methods with +@code{__attribute__ ((visibility ("hidden")))} so that they do not +appear in the export table of a DSO and do not require a PLT indirection +when used within the DSO@. Enabling this option can have a dramatic effect +on load and link times of a DSO as it massively reduces the size of the +dynamic export table when the library makes heavy use of templates. + +The behaviour of this switch is not quite the same as marking the +methods as hidden directly, because it does not affect static variables +local to the function or cause the compiler to deduce that +the function is defined in only one shared object. + +You may mark a method as having a visibility explicitly to negate the +effect of the switch for that method. For example, if you do want to +compare pointers to a particular inline method, you might mark it as +having default visibility. Marking the enclosing class with explicit +visibility will have no effect. + +Explicitly instantiated inline methods are unaffected by this option +as their linkage might otherwise cross a shared library boundary. +@xref{Template Instantiation}. + +@c APPLE LOCAL begin mainline 2007-06-28 ms tinfo compat 4230099 +@item -fvisibility-ms-compat +@opindex fvisibility-ms-compat +This flag attempts to use visibility settings to make GCC's C++ +linkage model compatible with that of Microsoft Visual Studio. + +The flag makes these changes to GCC's linkage model: + +1. It sets the default visibility to 'hidden', like +@option{-fvisibility=hidden}. +2. Types, but not their members, are not hidden by default. +3. The One Definition Rule is relaxed for types without explicit +visibility specifications which are defined in more than one different +shared object: those declarations are permitted if they would have +been permitted when this option was not used. + +This option is discouraged, rather, it is preferable for types to be +explicitly exported as desired on a per-class basis. Unfortunately +because Visual Studio can't compare two different hidden types as +unequal for the purposes of type_info and exception handling, users +are able to write code that relies upon this behavior. + +Among the consequences of these changes are that static data members +of the same type with the same name but defined in different shared +objects will be different, so changing one will not change the other; +and that pointers to function members defined in different shared +objects will not compare equal. When this flag is given, it is a +violation of the ODR to define types with the same name differently. +@c APPLE LOCAL end mainline 2007-06-28 ms tinfo compat 4230099 + +@item -fno-weak +@opindex fno-weak +Do not use weak symbol support, even if it is provided by the linker. +By default, G++ will use weak symbols if they are available. This +option exists only for testing, and should not be used by end-users; +it will result in inferior code and has no benefits. This option may +be removed in a future release of G++. + +@item -nostdinc++ +@opindex nostdinc++ +Do not search for header files in the standard directories specific to +C++, but do still search the other standard directories. (This option +is used when building the C++ library.) +@end table + +In addition, these optimization, warning, and code generation options +have meanings only for C++ programs: + +@table @gcctabopt +@item -fno-default-inline +@opindex fno-default-inline +Do not assume @samp{inline} for functions defined inside a class scope. +@xref{Optimize Options,,Options That Control Optimization}. Note that these +functions will have linkage like inline functions; they just won't be +inlined by default. + +@item -Wabi @r{(C++ only)} +@opindex Wabi +Warn when G++ generates code that is probably not compatible with the +vendor-neutral C++ ABI@. Although an effort has been made to warn about +all such cases, there are probably some cases that are not warned about, +even though G++ is generating incompatible code. There may also be +cases where warnings are emitted even though the code that is generated +will be compatible. + +You should rewrite your code to avoid these warnings if you are +concerned about the fact that code generated by G++ may not be binary +compatible with code generated by other compilers. + +The known incompatibilities at this point include: + +@itemize @bullet + +@item +Incorrect handling of tail-padding for bit-fields. G++ may attempt to +pack data into the same byte as a base class. For example: + +@smallexample +struct A @{ virtual void f(); int f1 : 1; @}; +struct B : public A @{ int f2 : 1; @}; +@end smallexample + +@noindent +In this case, G++ will place @code{B::f2} into the same byte +as@code{A::f1}; other compilers will not. You can avoid this problem +by explicitly padding @code{A} so that its size is a multiple of the +byte size on your platform; that will cause G++ and other compilers to +layout @code{B} identically. + +@item +Incorrect handling of tail-padding for virtual bases. G++ does not use +tail padding when laying out virtual bases. For example: + +@smallexample +struct A @{ virtual void f(); char c1; @}; +struct B @{ B(); char c2; @}; +struct C : public A, public virtual B @{@}; +@end smallexample + +@noindent +In this case, G++ will not place @code{B} into the tail-padding for +@code{A}; other compilers will. You can avoid this problem by +explicitly padding @code{A} so that its size is a multiple of its +alignment (ignoring virtual base classes); that will cause G++ and other +compilers to layout @code{C} identically. + +@item +Incorrect handling of bit-fields with declared widths greater than that +of their underlying types, when the bit-fields appear in a union. For +example: + +@smallexample +union U @{ int i : 4096; @}; +@end smallexample + +@noindent +Assuming that an @code{int} does not have 4096 bits, G++ will make the +union too small by the number of bits in an @code{int}. + +@item +Empty classes can be placed at incorrect offsets. For example: + +@smallexample +struct A @{@}; + +struct B @{ + A a; + virtual void f (); +@}; + +struct C : public B, public A @{@}; +@end smallexample + +@noindent +G++ will place the @code{A} base class of @code{C} at a nonzero offset; +it should be placed at offset zero. G++ mistakenly believes that the +@code{A} data member of @code{B} is already at offset zero. + +@item +Names of template functions whose types involve @code{typename} or +template template parameters can be mangled incorrectly. + +@smallexample +template <typename Q> +void f(typename Q::X) @{@} + +template <template <typename> class Q> +void f(typename Q<int>::X) @{@} +@end smallexample + +@noindent +Instantiations of these templates may be mangled incorrectly. + +@end itemize + +@item -Wctor-dtor-privacy @r{(C++ only)} +@opindex Wctor-dtor-privacy +Warn when a class seems unusable because all the constructors or +destructors in that class are private, and it has neither friends nor +public static member functions. + +@item -Wnon-virtual-dtor @r{(C++ only)} +@opindex Wnon-virtual-dtor +Warn when a class appears to be polymorphic, thereby requiring a virtual +destructor, yet it declares a non-virtual one. This warning is also +enabled if -Weffc++ is specified. + +@item -Wreorder @r{(C++ only)} +@opindex Wreorder +@cindex reordering, warning +@cindex warning for reordering of member initializers +Warn when the order of member initializers given in the code does not +match the order in which they must be executed. For instance: + +@smallexample +struct A @{ + int i; + int j; + A(): j (0), i (1) @{ @} +@}; +@end smallexample + +The compiler will rearrange the member initializers for @samp{i} +and @samp{j} to match the declaration order of the members, emitting +a warning to that effect. This warning is enabled by @option{-Wall}. +@end table + +The following @option{-W@dots{}} options are not affected by @option{-Wall}. + +@table @gcctabopt +@item -Weffc++ @r{(C++ only)} +@opindex Weffc++ +Warn about violations of the following style guidelines from Scott Meyers' +@cite{Effective C++} book: + +@itemize @bullet +@item +Item 11: Define a copy constructor and an assignment operator for classes +with dynamically allocated memory. + +@item +Item 12: Prefer initialization to assignment in constructors. + +@item +Item 14: Make destructors virtual in base classes. + +@item +Item 15: Have @code{operator=} return a reference to @code{*this}. + +@item +Item 23: Don't try to return a reference when you must return an object. + +@end itemize + +Also warn about violations of the following style guidelines from +Scott Meyers' @cite{More Effective C++} book: + +@itemize @bullet +@item +Item 6: Distinguish between prefix and postfix forms of increment and +decrement operators. + +@item +Item 7: Never overload @code{&&}, @code{||}, or @code{,}. + +@end itemize + +When selecting this option, be aware that the standard library +headers do not obey all of these guidelines; use @samp{grep -v} +to filter out those warnings. + +@item -Wno-deprecated @r{(C++ only)} +@opindex Wno-deprecated +Do not warn about usage of deprecated features. @xref{Deprecated Features}. + +@item -Wstrict-null-sentinel @r{(C++ only)} +@opindex Wstrict-null-sentinel +Warn also about the use of an uncasted @code{NULL} as sentinel. When +compiling only with GCC this is a valid sentinel, as @code{NULL} is defined +to @code{__null}. Although it is a null pointer constant not a null pointer, +it is guaranteed to of the same size as a pointer. But this use is +not portable across different compilers. + +@item -Wno-non-template-friend @r{(C++ only)} +@opindex Wno-non-template-friend +Disable warnings when non-templatized friend functions are declared +within a template. Since the advent of explicit template specification +support in G++, if the name of the friend is an unqualified-id (i.e., +@samp{friend foo(int)}), the C++ language specification demands that the +friend declare or define an ordinary, nontemplate function. (Section +14.5.3). Before G++ implemented explicit specification, unqualified-ids +could be interpreted as a particular specialization of a templatized +function. Because this non-conforming behavior is no longer the default +behavior for G++, @option{-Wnon-template-friend} allows the compiler to +check existing code for potential trouble spots and is on by default. +This new compiler behavior can be turned off with +@option{-Wno-non-template-friend} which keeps the conformant compiler code +but disables the helpful warning. + +@item -Wold-style-cast @r{(C++ only)} +@opindex Wold-style-cast +Warn if an old-style (C-style) cast to a non-void type is used within +a C++ program. The new-style casts (@samp{dynamic_cast}, +@samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are +less vulnerable to unintended effects and much easier to search for. + +@item -Woverloaded-virtual @r{(C++ only)} +@opindex Woverloaded-virtual +@cindex overloaded virtual fn, warning +@cindex warning for overloaded virtual fn +Warn when a function declaration hides virtual functions from a +base class. For example, in: + +@smallexample +struct A @{ + virtual void f(); +@}; + +struct B: public A @{ + void f(int); +@}; +@end smallexample + +the @code{A} class version of @code{f} is hidden in @code{B}, and code +like: + +@smallexample +B* b; +b->f(); +@end smallexample + +will fail to compile. + +@item -Wno-pmf-conversions @r{(C++ only)} +@opindex Wno-pmf-conversions +Disable the diagnostic for converting a bound pointer to member function +to a plain pointer. + +@item -Wsign-promo @r{(C++ only)} +@opindex Wsign-promo +Warn when overload resolution chooses a promotion from unsigned or +enumerated type to a signed type, over a conversion to an unsigned type of +the same size. Previous versions of G++ would try to preserve +unsignedness, but the standard mandates the current behavior. + +@smallexample +struct A @{ + operator int (); + A& operator = (int); +@}; + +main () +@{ + A a,b; + a = b; +@} +@end smallexample + +In this example, G++ will synthesize a default @samp{A& operator = +(const A&);}, while cfront will use the user-defined @samp{operator =}. +@end table + +@node Objective-C and Objective-C++ Dialect Options +@section Options Controlling Objective-C and Objective-C++ Dialects + +@cindex compiler options, Objective-C and Objective-C++ +@cindex Objective-C and Objective-C++ options, command line +@cindex options, Objective-C and Objective-C++ +(NOTE: This manual does not describe the Objective-C and Objective-C++ +languages themselves. See @xref{Standards,,Language Standards +Supported by GCC}, for references.) + +This section describes the command-line options that are only meaningful +for Objective-C and Objective-C++ programs, but you can also use most of +the language-independent GNU compiler options. +For example, you might compile a file @code{some_class.m} like this: + +@smallexample +gcc -g -fgnu-runtime -O -c some_class.m +@end smallexample + +@noindent +In this example, @option{-fgnu-runtime} is an option meant only for +Objective-C and Objective-C++ programs; you can use the other options with +any language supported by GCC@. + +Note that since Objective-C is an extension of the C language, Objective-C +compilations may also use options specific to the C front-end (e.g., +@option{-Wtraditional}). Similarly, Objective-C++ compilations may use +C++-specific options (e.g., @option{-Wabi}). + +Here is a list of options that are @emph{only} for compiling Objective-C +and Objective-C++ programs: + +@table @gcctabopt +@item -fconstant-string-class=@var{class-name} +@opindex fconstant-string-class +Use @var{class-name} as the name of the class to instantiate for each +literal string specified with the syntax @code{@@"@dots{}"}. The default +class name is @code{NXConstantString} if the GNU runtime is being used, and +@code{NSConstantString} if the NeXT runtime is being used (see below). The +@option{-fconstant-cfstrings} option, if also present, will override the +@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals +to be laid out as constant CoreFoundation strings. + +@item -fgnu-runtime +@opindex fgnu-runtime +Generate object code compatible with the standard GNU Objective-C +runtime. This is the default for most types of systems. + +@item -fnext-runtime +@opindex fnext-runtime +Generate output compatible with the NeXT runtime. This is the default +for NeXT-based systems, including Darwin and Mac OS X@. The macro +@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is +used. + +@item -fno-nil-receivers +@opindex fno-nil-receivers +Assume that all Objective-C message dispatches (e.g., +@code{[receiver message:arg]}) in this translation unit ensure that the receiver +is not @code{nil}. This allows for more efficient entry points in the runtime +to be used. Currently, this option is only available in conjunction with +the NeXT runtime on Mac OS X 10.3 and later. + +@item -fobjc-call-cxx-cdtors +@opindex fobjc-call-cxx-cdtors +For each Objective-C class, check if any of its instance variables is a +C++ object with a non-trivial default constructor. If so, synthesize a +special @code{- (id) .cxx_construct} instance method that will run +non-trivial default constructors on any such instance variables, in order, +and then return @code{self}. Similarly, check if any instance variable +is a C++ object with a non-trivial destructor, and if so, synthesize a +special @code{- (void) .cxx_destruct} method that will run +all such default destructors, in reverse order. + +The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods +thusly generated will only operate on instance variables declared in the +current Objective-C class, and not those inherited from superclasses. It +is the responsibility of the Objective-C runtime to invoke all such methods +in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods +will be invoked by the runtime immediately after a new object +instance is allocated; the @code{- (void) .cxx_destruct} methods will +be invoked immediately before the runtime deallocates an object instance. + +As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has +support for invoking the @code{- (id) .cxx_construct} and +@code{- (void) .cxx_destruct} methods. + +@item -fobjc-direct-dispatch +@opindex fobjc-direct-dispatch +Allow fast jumps to the message dispatcher. On Darwin this is +accomplished via the comm page. + +@c APPLE LOCAL begin radar 4512786 +@item -fobjc-sjlj-exceptions +@opindex fobjc-sjlj-exceptions +Enable syntactic support for structured exception handling in Objective-C, +similar to what is offered by C++ and Java. This option is +unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and +earlier. +This option is on by default with the NeXT runtime. +@c APPLE LOCAL end radar 4512786 + +@smallexample + @@try @{ + @dots{} + @@throw expr; + @dots{} + @} + @@catch (AnObjCClass *exc) @{ + @dots{} + @@throw expr; + @dots{} + @@throw; + @dots{} + @} + @@catch (AnotherClass *exc) @{ + @dots{} + @} + @@catch (id allOthers) @{ + @dots{} + @} + @@finally @{ + @dots{} + @@throw expr; + @dots{} + @} +@end smallexample + +The @code{@@throw} statement may appear anywhere in an Objective-C or +Objective-C++ program; when used inside of a @code{@@catch} block, the +@code{@@throw} may appear without an argument (as shown above), in which case +the object caught by the @code{@@catch} will be rethrown. + +Note that only (pointers to) Objective-C objects may be thrown and +caught using this scheme. When an object is thrown, it will be caught +by the nearest @code{@@catch} clause capable of handling objects of that type, +analogously to how @code{catch} blocks work in C++ and Java. A +@code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch +any and all Objective-C exceptions not caught by previous @code{@@catch} +clauses (if any). + +The @code{@@finally} clause, if present, will be executed upon exit from the +immediately preceding @code{@@try @dots{} @@catch} section. This will happen +regardless of whether any exceptions are thrown, caught or rethrown +inside the @code{@@try @dots{} @@catch} section, analogously to the behavior +of the @code{finally} clause in Java. + +There are several caveats to using the new exception mechanism: + +@itemize @bullet +@item +Although currently designed to be binary compatible with @code{NS_HANDLER}-style +idioms provided by the @code{NSException} class, the new +exceptions can only be used on Mac OS X 10.3 (Panther) and later +systems, due to additional functionality needed in the (NeXT) Objective-C +runtime. + +@item +As mentioned above, the new exceptions do not support handling +types other than Objective-C objects. Furthermore, when used from +Objective-C++, the Objective-C exception model does not interoperate with C++ +exceptions at this time. This means you cannot @code{@@throw} an exception +from Objective-C and @code{catch} it in C++, or vice versa +(i.e., @code{throw @dots{} @@catch}). +@end itemize + +@c APPLE LOCAL radar 4512786 +The @option{-fobjc-sjlj-exceptions} switch also enables the use of synchronization +blocks for thread-safe execution: + +@smallexample + @@synchronized (ObjCClass *guard) @{ + @dots{} + @} +@end smallexample + +Upon entering the @code{@@synchronized} block, a thread of execution shall +first check whether a lock has been placed on the corresponding @code{guard} +object by another thread. If it has, the current thread shall wait until +the other thread relinquishes its lock. Once @code{guard} becomes available, +the current thread will place its own lock on it, execute the code contained in +the @code{@@synchronized} block, and finally relinquish the lock (thereby +making @code{guard} available to other threads). + +Unlike Java, Objective-C does not allow for entire methods to be marked +@code{@@synchronized}. Note that throwing exceptions out of +@code{@@synchronized} blocks is allowed, and will cause the guarding object +to be unlocked properly. + +@item -fobjc-gc +@opindex fobjc-gc +Enable garbage collection (GC) in Objective-C and Objective-C++ programs. +@c APPLE LOCAL begin radar 5780114 - ObjC GC +The resulting binary requires additional runtime support which is present on +Mac OS X Version 10.5 (Leopard) and later. All Objective-C objects are presumed +to be garbage collected. To aid in this effort, compiler implements assignments +of Objective-C object pointers via runtime support functions. These functions work +correctly in non-GC environments as well, in case this code is used as part of a +library. Assignments of objects into instance variables of other objects are +intercepted, so are assignments to global object variables. In general, assignments +through pointers to objects are intercepted. Additionally, assignments of objects +as fields within structures are intercepted. + +In addition, other pointer variables may be marked with the __strong storage class +modifier to indicate to the compiler that these assignments need to use the assignment +runtime functions as well, allowing the memory referenced by these pointers to be +allocated from the collector. A __weak storage class modifier for pointers is also +introduced to indicate a zero-ing weak reference. This is permitted only for instance +variables of an object or globals. The compiler arranges for all reads as well as +writes to these variables to occur via runtime support functions. Under garbage +collection these variables are not consulted when determining what is not garbage +and they are set to nil (zero) if the memory they reference is deemed garbage and is +collected. + +@smallexample + __strong void *p; // assignments to 'p' will have runtime support calls + int *q; // assignments to 'q' ordinarly will not + @dots{} + (__strong int *)q = 0; // this assignment will call a runtime support function +@end smallexample + +Conversely, the @code{__weak} type qualifier may be used to call weak runtime +functions. + +@smallexample + __weak id q; // assignments to 'q' will have the '__weak' semantics + id p; // assignments to 'p' will have the "__strong' semantics + @dots{} + (__weak id)p = 0; // Fall back to '__weak' semantics in this assignment. +@end smallexample + +@item -fobjc-gc-only +@opindex fobjc-gc-only +Use this option to indicate that the Objective-C program supports garbage +collection (GC) only - that is, it does not contain retain/release logic. +This flag implies @option{-fobjc-gc} as well. With this flag, framework +is marked as not honoring retain/release. + +@c APPLE LOCAL end radar 5780114 - ObjC GC +@item -freplace-objc-classes +@opindex freplace-objc-classes +Emit a special marker instructing @command{ld(1)} not to statically link in +the resulting object file, and allow @command{dyld(1)} to load it in at +run time instead. This is used in conjunction with the Fix-and-Continue +debugging mode, where the object file in question may be recompiled and +dynamically reloaded in the course of program execution, without the need +to restart the program itself. Currently, Fix-and-Continue functionality +is only available in conjunction with the NeXT runtime on Mac OS X 10.3 +and later. + +@item -fzero-link +@opindex fzero-link +When compiling for the NeXT runtime, the compiler ordinarily replaces calls +to @code{objc_getClass("@dots{}")} (when the name of the class is known at +compile time) with static class references that get initialized at load time, +which improves run-time performance. Specifying the @option{-fzero-link} flag +suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} +to be retained. This is useful in Zero-Link debugging mode, since it allows +for individual class implementations to be modified during program execution. + +@item -gen-decls +@opindex gen-decls +Dump interface declarations for all classes seen in the source file to a +file named @file{@var{sourcename}.decl}. + +@item -Wassign-intercept +@opindex Wassign-intercept +Warn whenever an Objective-C assignment is being intercepted by the +garbage collector. + +@item -Wno-protocol +@opindex Wno-protocol +If a class is declared to implement a protocol, a warning is issued for +every method in the protocol that is not implemented by the class. The +default behavior is to issue a warning for every method not explicitly +implemented in the class, even if a method implementation is inherited +from the superclass. If you use the @option{-Wno-protocol} option, then +methods inherited from the superclass are considered to be implemented, +and no warning is issued for them. + +@item -Wselector +@opindex Wselector +Warn if multiple methods of different types for the same selector are +found during compilation. The check is performed on the list of methods +in the final stage of compilation. Additionally, a check is performed +for each selector appearing in a @code{@@selector(@dots{})} +expression, and a corresponding method for that selector has been found +during compilation. Because these checks scan the method table only at +the end of compilation, these warnings are not produced if the final +stage of compilation is not reached, for example because an error is +found during compilation, or because the @option{-fsyntax-only} option is +being used. + +@c APPLE LOCAL begin radar 5172645 +@item -Wproperty-assign-default +@opindex Wproperty-assign-default +Warn if no ``assign'', ``retain'', or ``copy'' attribute is specified on +a property of pointer to object type. Property is then assumed to be +``assign'' by default. +@c APPLE LOCAL end radar 5172645 + +@c APPLE LOCAL begin radar 5376125 +@item -Wdirect-ivar-access +@opindex Wdirect-ivar-access +Warn if ivar of pointer to object type is directly accessed in non-gc +mode, instead of using property syntax access. +@c APPLE LOCAL end radar 5376125 + +@item -Wstrict-selector-match +@opindex Wstrict-selector-match +Warn if multiple methods with differing argument and/or return types are +found for a given selector when attempting to send a message using this +selector to a receiver of type @code{id} or @code{Class}. When this flag +is off (which is the default behavior), the compiler will omit such warnings +if any differences found are confined to types which share the same size +and alignment. + +@item -Wundeclared-selector +@opindex Wundeclared-selector +Warn if a @code{@@selector(@dots{})} expression referring to an +undeclared selector is found. A selector is considered undeclared if no +method with that name has been declared before the +@code{@@selector(@dots{})} expression, either explicitly in an +@code{@@interface} or @code{@@protocol} declaration, or implicitly in +an @code{@@implementation} section. This option always performs its +checks as soon as a @code{@@selector(@dots{})} expression is found, +while @option{-Wselector} only performs its checks in the final stage of +compilation. This also enforces the coding style convention +that methods and selectors must be declared before being used. + +@item -print-objc-runtime-info +@opindex print-objc-runtime-info +Generate C header describing the largest structure that is passed by +value, if any. + +@end table + +@node Language Independent Options +@section Options to Control Diagnostic Messages Formatting +@cindex options to control diagnostics formatting +@cindex diagnostic messages +@cindex message formatting + +Traditionally, diagnostic messages have been formatted irrespective of +the output device's aspect (e.g.@: its width, @dots{}). The options described +below can be used to control the diagnostic messages formatting +algorithm, e.g.@: how many characters per line, how often source location +information should be reported. Right now, only the C++ front end can +honor these options. However it is expected, in the near future, that +the remaining front ends would be able to digest them correctly. + +@table @gcctabopt +@item -fmessage-length=@var{n} +@opindex fmessage-length +Try to format error messages so that they fit on lines of about @var{n} +characters. The default is 72 characters for @command{g++} and 0 for the rest of +the front ends supported by GCC@. If @var{n} is zero, then no +line-wrapping will be done; each error message will appear on a single +line. + +@opindex fdiagnostics-show-location +@item -fdiagnostics-show-location=once +Only meaningful in line-wrapping mode. Instructs the diagnostic messages +reporter to emit @emph{once} source location information; that is, in +case the message is too long to fit on a single physical line and has to +be wrapped, the source location won't be emitted (as prefix) again, +over and over, in subsequent continuation lines. This is the default +behavior. + +@item -fdiagnostics-show-location=every-line +Only meaningful in line-wrapping mode. Instructs the diagnostic +messages reporter to emit the same source location information (as +prefix) for physical lines that result from the process of breaking +a message which is too long to fit on a single line. + +@item -fdiagnostics-show-option +@opindex fdiagnostics-show-option +This option instructs the diagnostic machinery to add text to each +diagnostic emitted, which indicates which command line option directly +controls that diagnostic, when such an option is known to the +diagnostic machinery. + +@end table + +@node Warning Options +@section Options to Request or Suppress Warnings +@cindex options to control warnings +@cindex warning messages +@cindex messages, warning +@cindex suppressing warnings + +Warnings are diagnostic messages that report constructions which +are not inherently erroneous but which are risky or suggest there +may have been an error. + +You can request many specific warnings with options beginning @samp{-W}, +for example @option{-Wimplicit} to request warnings on implicit +declarations. Each of these specific warning options also has a +negative form beginning @samp{-Wno-} to turn off warnings; +for example, @option{-Wno-implicit}. This manual lists only one of the +two forms, whichever is not the default. + +The following options control the amount and kinds of warnings produced +by GCC; for further, language-specific options also refer to +@ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect +Options}. + +@table @gcctabopt +@cindex syntax checking +@item -fsyntax-only +@opindex fsyntax-only +Check the code for syntax errors, but don't do anything beyond that. + +@item -pedantic +@opindex pedantic +Issue all the warnings demanded by strict ISO C and ISO C++; +reject all programs that use forbidden extensions, and some other +programs that do not follow ISO C and ISO C++. For ISO C, follows the +version of the ISO C standard specified by any @option{-std} option used. + +Valid ISO C and ISO C++ programs should compile properly with or without +this option (though a rare few will require @option{-ansi} or a +@option{-std} option specifying the required version of ISO C)@. However, +without this option, certain GNU extensions and traditional C and C++ +features are supported as well. With this option, they are rejected. + +@option{-pedantic} does not cause warning messages for use of the +alternate keywords whose names begin and end with @samp{__}. Pedantic +warnings are also disabled in the expression that follows +@code{__extension__}. However, only system header files should use +these escape routes; application programs should avoid them. +@xref{Alternate Keywords}. + +Some users try to use @option{-pedantic} to check programs for strict ISO +C conformance. They soon find that it does not do quite what they want: +it finds some non-ISO practices, but not all---only those for which +ISO C @emph{requires} a diagnostic, and some others for which +diagnostics have been added. + +A feature to report any failure to conform to ISO C might be useful in +some instances, but would require considerable additional work and would +be quite different from @option{-pedantic}. We don't have plans to +support such a feature in the near future. + +Where the standard specified with @option{-std} represents a GNU +extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a +corresponding @dfn{base standard}, the version of ISO C on which the GNU +extended dialect is based. Warnings from @option{-pedantic} are given +where they are required by the base standard. (It would not make sense +for such warnings to be given only for features not in the specified GNU +C dialect, since by definition the GNU dialects of C include all +features the compiler supports with the given option, and there would be +nothing to warn about.) + +@item -pedantic-errors +@opindex pedantic-errors +Like @option{-pedantic}, except that errors are produced rather than +warnings. + +@item -w +@opindex w +Inhibit all warning messages. + +@item -Wno-import +@opindex Wno-import +Inhibit warning messages about the use of @samp{#import}. + +@c APPLE LOCAL begin -Wno-#warnings +@item -Wno-#warnings +@opindex Wno-#warnings +Inhibit warning messages issued by @samp{#warning}. +@c APPLE LOCAL end -Wno-#warnings + +@c APPLE LOCAL begin -Wextra-tokens 2001-08-02 --sts ** +@item -Wextra-tokens +@opindex Wextra-tokens +Warn about extra tokens at the end of prepreprocessor directives. (APPLE ONLY) +@c APPLE LOCAL end -Wextra-tokens 2001-08-02 --sts ** + +@c APPLE LOCAL begin -Wnewline-eof 2001-08-23 --sts ** +@item -Wnewline-eof +@opindex Wnewline-eof +Warn about files missing a newline at the end of the file. (APPLE ONLY) +@c APPLE LOCAL end -Wnewline-eof 2001-08-23 --sts ** + +@c APPLE LOCAL begin -Wno-altivec-long-deprecated --ilr ** +@item -Wno-altivec-long-deprecated +@opindex Wno-altivec-long-deprecated +Do not warn about the use of the deprecated 'long' keyword in +AltiVec data types. (APPLE ONLY) +@c APPLE LOCAL end -Wno-altivec-long-deprecated --ilr ** + +@item -Wchar-subscripts +@opindex Wchar-subscripts +Warn if an array subscript has type @code{char}. This is a common cause +of error, as programmers often forget that this type is signed on some +machines. +This warning is enabled by @option{-Wall}. + +@item -Wcomment +@opindex Wcomment +Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} +comment, or whenever a Backslash-Newline appears in a @samp{//} comment. +This warning is enabled by @option{-Wall}. + +@item -Wfatal-errors +@opindex Wfatal-errors +This option causes the compiler to abort compilation on the first error +occurred rather than trying to keep going and printing further error +messages. + +@c APPLE LOCAL begin default to Wformat-security 5764921 +@item -Wno-format +@opindex Wno-format +@c APPLE LOCAL end default to Wformat-security 5764921 +@opindex ffreestanding +@opindex fno-builtin +Check calls to @code{printf} and @code{scanf}, etc., to make sure that +the arguments supplied have types appropriate to the format string +specified, and that the conversions specified in the format string make +sense. This includes standard functions, and others specified by format +attributes (@pxref{Function Attributes}), in the @code{printf}, +@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, +not in the C standard) families (or other target-specific families). +Which functions are checked without format attributes having been +specified depends on the standard version selected, and such checks of +functions without the attribute specified are disabled by +@option{-ffreestanding} or @option{-fno-builtin}. + +The formats are checked against the format features supported by GNU +libc version 2.2. These include all ISO C90 and C99 features, as well +as features from the Single Unix Specification and some BSD and GNU +extensions. Other library implementations may not support all these +features; GCC does not support warning about features that go beyond a +particular library's limitations. However, if @option{-pedantic} is used +with @option{-Wformat}, warnings will be given about format features not +in the selected standard version (but not for @code{strfmon} formats, +since those are not in any version of the C standard). @xref{C Dialect +Options,,Options Controlling C Dialect}. + +Since @option{-Wformat} also checks for null format arguments for +several functions, @option{-Wformat} also implies @option{-Wnonnull}. + +@option{-Wformat} is included in @option{-Wall}. For more control over some +aspects of format checking, the options @option{-Wformat-y2k}, +@option{-Wno-format-extra-args}, @option{-Wno-format-zero-length}, +@option{-Wformat-nonliteral}, @option{-Wformat-security}, and +@option{-Wformat=2} are available, but are not included in @option{-Wall}. + +@item -Wformat-y2k +@opindex Wformat-y2k +If @option{-Wformat} is specified, also warn about @code{strftime} +formats which may yield only a two-digit year. + +@item -Wno-format-extra-args +@opindex Wno-format-extra-args +If @option{-Wformat} is specified, do not warn about excess arguments to a +@code{printf} or @code{scanf} format function. The C standard specifies +that such arguments are ignored. + +Where the unused arguments lie between used arguments that are +specified with @samp{$} operand number specifications, normally +warnings are still given, since the implementation could not know what +type to pass to @code{va_arg} to skip the unused arguments. However, +in the case of @code{scanf} formats, this option will suppress the +warning if the unused arguments are all pointers, since the Single +Unix Specification says that such unused arguments are allowed. + +@item -Wno-format-zero-length +@opindex Wno-format-zero-length +If @option{-Wformat} is specified, do not warn about zero-length formats. +The C standard specifies that zero-length formats are allowed. + +@item -Wformat-nonliteral +@opindex Wformat-nonliteral +If @option{-Wformat} is specified, also warn if the format string is not a +string literal and so cannot be checked, unless the format function +takes its format arguments as a @code{va_list}. + +@c APPLE LOCAL begin default to Wformat-security 5764921 +@item -Wno-format-security +@opindex Wno-format-security +@c APPLE LOCAL end default to Wformat-security 5764921 +If @option{-Wformat} is specified, also warn about uses of format +functions that represent possible security problems. At present, this +warns about calls to @code{printf} and @code{scanf} functions where the +format string is not a string literal and there are no format arguments, +as in @code{printf (foo);}. This may be a security hole if the format +string came from untrusted input and contains @samp{%n}. (This is +currently a subset of what @option{-Wformat-nonliteral} warns about, but +in future warnings may be added to @option{-Wformat-security} that are not +included in @option{-Wformat-nonliteral}.) + +@item -Wformat=2 +@opindex Wformat=2 +Enable @option{-Wformat} plus format checks not included in +@option{-Wformat}. Currently equivalent to @samp{-Wformat +-Wformat-nonliteral -Wformat-security -Wformat-y2k}. + +@item -Wnonnull +@opindex Wnonnull +Warn about passing a null pointer for arguments marked as +requiring a non-null value by the @code{nonnull} function attribute. + +@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It +can be disabled with the @option{-Wno-nonnull} option. + +@c APPLE LOCAL begin Wglobal-constructors 6324584 +@item -Wglobal-constructors +@opindex Wglobal-constructors +Warn about namespace scope data that requires construction or +destruction, or functions that use the constructor attribute or the +destructor attribute. Additionally warn if the Objective-C GNU +runtime is used to initialize various metadata. +@c APPLE LOCAL end Wglobal-constructors 6324584 + +@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Winit-self +Warn about uninitialized variables which are initialized with themselves. +Note this option can only be used with the @option{-Wuninitialized} option, +which in turn only works with @option{-O1} and above. + +For example, GCC will warn about @code{i} being uninitialized in the +following snippet only when @option{-Winit-self} has been specified: +@smallexample +@group +int f() +@{ + int i = i; + return i; +@} +@end group +@end smallexample + +@item -Wimplicit-int +@opindex Wimplicit-int +Warn when a declaration does not specify a type. +This warning is enabled by @option{-Wall}. + +@item -Wimplicit-function-declaration +@itemx -Werror-implicit-function-declaration +@opindex Wimplicit-function-declaration +@opindex Werror-implicit-function-declaration +Give a warning (or error) whenever a function is used before being +declared. The form @option{-Wno-error-implicit-function-declaration} +is not supported. +This warning is enabled by @option{-Wall} (as a warning, not an error). + +@item -Wimplicit +@opindex Wimplicit +Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. +This warning is enabled by @option{-Wall}. + +@item -Wmain +@opindex Wmain +Warn if the type of @samp{main} is suspicious. @samp{main} should be a +function with external linkage, returning int, taking either zero +arguments, two, or three arguments of appropriate types. +This warning is enabled by @option{-Wall}. + +@item -Wmissing-braces +@opindex Wmissing-braces +Warn if an aggregate or union initializer is not fully bracketed. In +the following example, the initializer for @samp{a} is not fully +bracketed, but that for @samp{b} is fully bracketed. + +@smallexample +int a[2][2] = @{ 0, 1, 2, 3 @}; +int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Wmissing-include-dirs +Warn if a user-supplied include directory does not exist. + +@item -Wparentheses +@opindex Wparentheses +Warn if parentheses are omitted in certain contexts, such +as when there is an assignment in a context where a truth value +is expected, or when operators are nested whose precedence people +often get confused about. Only the warning for an assignment used as +a truth value is supported when compiling C++; the other warnings are +only supported when compiling C@. + +Also warn if a comparison like @samp{x<=y<=z} appears; this is +equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different +interpretation from that of ordinary mathematical notation. + +Also warn about constructions where there may be confusion to which +@code{if} statement an @code{else} branch belongs. Here is an example of +such a case: + +@smallexample +@group +@{ + if (a) + if (b) + foo (); + else + bar (); +@} +@end group +@end smallexample + +In C, every @code{else} branch belongs to the innermost possible @code{if} +statement, which in this example is @code{if (b)}. This is often not +what the programmer expected, as illustrated in the above example by +indentation the programmer chose. When there is the potential for this +confusion, GCC will issue a warning when this flag is specified. +To eliminate the warning, add explicit braces around the innermost +@code{if} statement so there is no way the @code{else} could belong to +the enclosing @code{if}. The resulting code would look like this: + +@smallexample +@group +@{ + if (a) + @{ + if (b) + foo (); + else + bar (); + @} +@} +@end group +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wsequence-point +@opindex Wsequence-point +Warn about code that may have undefined semantics because of violations +of sequence point rules in the C and C++ standards. + +The C and C++ standards defines the order in which expressions in a C/C++ +program are evaluated in terms of @dfn{sequence points}, which represent +a partial ordering between the execution of parts of the program: those +executed before the sequence point, and those executed after it. These +occur after the evaluation of a full expression (one which is not part +of a larger expression), after the evaluation of the first operand of a +@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a +function is called (but after the evaluation of its arguments and the +expression denoting the called function), and in certain other places. +Other than as expressed by the sequence point rules, the order of +evaluation of subexpressions of an expression is not specified. All +these rules describe only a partial order rather than a total order, +since, for example, if two functions are called within one expression +with no sequence point between them, the order in which the functions +are called is not specified. However, the standards committee have +ruled that function calls do not overlap. + +It is not specified when between sequence points modifications to the +values of objects take effect. Programs whose behavior depends on this +have undefined behavior; the C and C++ standards specify that ``Between +the previous and next sequence point an object shall have its stored +value modified at most once by the evaluation of an expression. +Furthermore, the prior value shall be read only to determine the value +to be stored.''. If a program breaks these rules, the results on any +particular implementation are entirely unpredictable. + +Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] += b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not +diagnosed by this option, and it may give an occasional false positive +result, but in general it has been found fairly effective at detecting +this sort of problem in programs. + +The standard is worded confusingly, therefore there is some debate +over the precise meaning of the sequence point rules in subtle cases. +Links to discussions of the problem, including proposed formal +definitions, may be found on the GCC readings page, at +@w{@uref{http://gcc.gnu.org/readings.html}}. + +This warning is enabled by @option{-Wall} for C and C++. + +@item -Wreturn-type +@opindex Wreturn-type +Warn whenever a function is defined with a return-type that defaults to +@code{int}. Also warn about any @code{return} statement with no +return-value in a function whose return-type is not @code{void}. + +For C, also warn if the return type of a function has a type qualifier +such as @code{const}. Such a type qualifier has no effect, since the +value returned by a function is not an lvalue. ISO C prohibits +qualified @code{void} return types on function definitions, so such +return types always receive a warning even without this option. + +For C++, a function without return type always produces a diagnostic +message, even when @option{-Wno-return-type} is specified. The only +exceptions are @samp{main} and functions defined in system headers. + +This warning is enabled by @option{-Wall}. + +@item -Wswitch +@opindex Wswitch +Warn whenever a @code{switch} statement has an index of enumerated type +and lacks a @code{case} for one or more of the named codes of that +enumeration. (The presence of a @code{default} label prevents this +warning.) @code{case} labels outside the enumeration range also +provoke warnings when this option is used. +This warning is enabled by @option{-Wall}. + +@item -Wswitch-default +@opindex Wswitch-switch +Warn whenever a @code{switch} statement does not have a @code{default} +case. + +@item -Wswitch-enum +@opindex Wswitch-enum +Warn whenever a @code{switch} statement has an index of enumerated type +and lacks a @code{case} for one or more of the named codes of that +enumeration. @code{case} labels outside the enumeration range also +provoke warnings when this option is used. + +@item -Wtrigraphs +@opindex Wtrigraphs +Warn if any trigraphs are encountered that might change the meaning of +the program (trigraphs within comments are not warned about). +This warning is enabled by @option{-Wall}. + +@item -Wunused-function +@opindex Wunused-function +Warn whenever a static function is declared but not defined or a +non-inline static function is unused. +This warning is enabled by @option{-Wall}. + +@item -Wunused-label +@opindex Wunused-label +Warn whenever a label is declared but not used. +This warning is enabled by @option{-Wall}. + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-parameter +@opindex Wunused-parameter +Warn whenever a function parameter is unused aside from its declaration. + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-variable +@opindex Wunused-variable +Warn whenever a local variable or non-constant static variable is unused +aside from its declaration. +This warning is enabled by @option{-Wall}. + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-value +@opindex Wunused-value +Warn whenever a statement computes a result that is explicitly not used. +This warning is enabled by @option{-Wall}. + +To suppress this warning cast the expression to @samp{void}. + +@item -Wunused +@opindex Wunused +All the above @option{-Wunused} options combined. + +In order to get a warning about an unused function parameter, you must +either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies +@samp{-Wunused}), or separately specify @option{-Wunused-parameter}. + +@item -Wuninitialized +@opindex Wuninitialized +Warn if an automatic variable is used without first being initialized or +if a variable may be clobbered by a @code{setjmp} call. + +These warnings are possible only in optimizing compilation, +because they require data flow information that is computed only +when optimizing. If you do not specify @option{-O}, you will not get +these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized} +requiring @option{-O}. + +If you want to warn about code which uses the uninitialized value of the +variable in its own initializer, use the @option{-Winit-self} option. + +These warnings occur for individual uninitialized or clobbered +elements of structure, union or array variables as well as for +variables which are uninitialized or clobbered as a whole. They do +not occur for variables or elements declared @code{volatile}. Because +these warnings depend on optimization, the exact variables or elements +for which there are warnings will depend on the precise optimization +options and version of GCC used. + +Note that there may be no warning about a variable that is used only +to compute a value that itself is never used, because such +computations may be deleted by data flow analysis before the warnings +are printed. + +These warnings are made optional because GCC is not smart +enough to see all the reasons why the code might be correct +despite appearing to have an error. Here is one example of how +this can happen: + +@smallexample +@group +@{ + int x; + switch (y) + @{ + case 1: x = 1; + break; + case 2: x = 4; + break; + case 3: x = 5; + @} + foo (x); +@} +@end group +@end smallexample + +@noindent +If the value of @code{y} is always 1, 2 or 3, then @code{x} is +always initialized, but GCC doesn't know this. Here is +another common case: + +@smallexample +@{ + int save_y; + if (change_y) save_y = y, y = new_y; + @dots{} + if (change_y) y = save_y; +@} +@end smallexample + +@noindent +This has no bug because @code{save_y} is used only if it is set. + +@cindex @code{longjmp} warnings +This option also warns when a non-volatile automatic variable might be +changed by a call to @code{longjmp}. These warnings as well are possible +only in optimizing compilation. + +The compiler sees only the calls to @code{setjmp}. It cannot know +where @code{longjmp} will be called; in fact, a signal handler could +call it at any point in the code. As a result, you may get a warning +even when there is in fact no problem because @code{longjmp} cannot +in fact be called at the place which would cause a problem. + +Some spurious warnings can be avoided if you declare all the functions +you use that never return as @code{noreturn}. @xref{Function +Attributes}. + +This warning is enabled by @option{-Wall}. + +@item -Wunknown-pragmas +@opindex Wunknown-pragmas +@cindex warning for unknown pragmas +@cindex unknown pragmas, warning +@cindex pragmas, warning of unknown +Warn when a #pragma directive is encountered which is not understood by +GCC@. If this command line option is used, warnings will even be issued +for unknown pragmas in system header files. This is not the case if +the warnings were only enabled by the @option{-Wall} command line option. + +@item -Wno-pragmas +@opindex Wno-pragmas +@opindex Wpragmas +Do not warn about misuses of pragmas, such as incorrect parameters, +invalid syntax, or conflicts between pragmas. See also +@samp{-Wunknown-pragmas}. + +@item -Wstrict-aliasing +@opindex Wstrict-aliasing +This option is only active when @option{-fstrict-aliasing} is active. +It warns about code which might break the strict aliasing rules that the +compiler is using for optimization. The warning does not catch all +cases, but does attempt to catch the more common pitfalls. It is +included in @option{-Wall}. + +@item -Wstrict-aliasing=2 +@opindex Wstrict-aliasing=2 +This option is only active when @option{-fstrict-aliasing} is active. +It warns about code which might break the strict aliasing rules that the +compiler is using for optimization. This warning catches more cases than +@option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous +cases that are safe. + +@item -Wstrict-overflow +@item -Wstrict-overflow=@var{n} +@opindex Wstrict-overflow +This option is only active when @option{-fstrict-overflow} is active. +It warns about cases where the compiler optimizes based on the +assumption that signed overflow does not occur. Note that it does not +warn about all cases where the code might overflow: it only warns +about cases where the compiler implements some optimization. Thus +this warning depends on the optimization level. + +An optimization which assumes that signed overflow does not occur is +perfectly safe if the values of the variables involved are such that +overflow never does, in fact, occur. Therefore this warning can +easily give a false positive: a warning about code which is not +actually a problem. To help focus on important issues, several +warning levels are defined. No warnings are issued for the use of +undefined signed overflow when estimating how many iterations a loop +will require, in particular when determining whether a loop will be +executed at all. + +@c APPLE LOCAL mainline man page 6365204 +@table @gcctabopt +@item -Wstrict-overflow=1 +Warn about cases which are both questionable and easy to avoid. For +example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the +compiler will simplify this to @code{1}. This level of +@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels +are not, and must be explicitly requested. + +@item -Wstrict-overflow=2 +Also warn about other cases where a comparison is simplified to a +constant. For example: @code{abs (x) >= 0}. This can only be +simplified when @option{-fstrict-overflow} is in effect, because +@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than +zero. @option{-Wstrict-overflow} (with no level) is the same as +@option{-Wstrict-overflow=2}. + +@item -Wstrict-overflow=3 +Also warn about other cases where a comparison is simplified. For +example: @code{x + 1 > 1} will be simplified to @code{x > 0}. + +@item -Wstrict-overflow=4 +Also warn about other simplifications not covered by the above cases. +For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}. + +@item -Wstrict-overflow=5 +Also warn about cases where the compiler reduces the magnitude of a +constant involved in a comparison. For example: @code{x + 2 > y} will +be simplified to @code{x + 1 >= y}. This is reported only at the +highest warning level because this simplification applies to many +comparisons, so this warning level will give a very large number of +false positives. +@end table + +@item -Wall +@opindex Wall +All of the above @samp{-W} options combined. This enables all the +warnings about constructions that some users consider questionable, and +that are easy to avoid (or modify to prevent the warning), even in +conjunction with macros. This also enables some language-specific +warnings described in @ref{C++ Dialect Options} and +@ref{Objective-C and Objective-C++ Dialect Options}. +@c APPLE LOCAL begin -Wmost +@item -Wmost +@opindex Wmost +This is equivalent to -Wall -Wno-parentheses. (APPLE ONLY) +@end table +@c APPLE LOCAL end -Wmost + +The following @option{-W@dots{}} options are not implied by @option{-Wall}. +Some of them warn about constructions that users generally do not +consider questionable, but which occasionally you might wish to check +for; others warn about constructions that are necessary or hard to avoid +in some cases, and there is no simple way to modify the code to suppress +the warning. + +@table @gcctabopt +@item -Wextra +@opindex W +@opindex Wextra +(This option used to be called @option{-W}. The older name is still +supported, but the newer name is more descriptive.) Print extra warning +messages for these events: + +@itemize @bullet +@item +A function can return either with or without a value. (Falling +off the end of the function body is considered returning without +a value.) For example, this function would evoke such a +warning: + +@smallexample +@group +foo (a) +@{ + if (a > 0) + return a; +@} +@end group +@end smallexample + +@item +An expression-statement or the left-hand side of a comma expression +contains no side effects. +To suppress the warning, cast the unused expression to void. +For example, an expression such as @samp{x[i,j]} will cause a warning, +but @samp{x[(void)i,j]} will not. + +@item +An unsigned value is compared against zero with @samp{<} or @samp{>=}. + +@item +Storage-class specifiers like @code{static} are not the first things in +a declaration. According to the C Standard, this usage is obsolescent. + +@item +If @option{-Wall} or @option{-Wunused} is also specified, warn about unused +arguments. + +@item +A comparison between signed and unsigned values could produce an +incorrect result when the signed value is converted to unsigned. +(But don't warn if @option{-Wno-sign-compare} is also specified.) + +@item +An aggregate has an initializer which does not initialize all members. +This warning can be independently controlled by +@option{-Wmissing-field-initializers}. + +@item +An initialized field without side effects is overridden when using +designated initializers (@pxref{Designated Inits, , Designated +Initializers}). This warning can be independently controlled by +@option{-Woverride-init}. + +@item +A function parameter is declared without a type specifier in K&R-style +functions: + +@smallexample +void foo(bar) @{ @} +@end smallexample + +@item +An empty body occurs in an @samp{if} or @samp{else} statement. + +@c APPLE LOCAL begin mainline +@c APPLE LOCAL begin pod error 6089368 +@item +(C++ only) An empty body occurs in a @samp{while} or @samp{for} statement with no +@c APPLE LOCAL end pod error 6089368 +whitespacing before the semicolon. This warning can be independently +controlled by @option{-Wempty-body}. +@c APPLE LOCAL end mainline + +@item +A pointer is compared against integer zero with @samp{<}, @samp{<=}, +@samp{>}, or @samp{>=}. + +@item +A variable might be changed by @samp{longjmp} or @samp{vfork}. + +@c APPLE LOCAL begin pod error 6089368 +@item +(C++ only) An enumerator and a non-enumerator both appear in a conditional expression. + +@item +(C++ only) A non-static reference or non-static @samp{const} member appears in a +class without constructors. + +@item +(C++ only) Ambiguous virtual bases. + +@item +(C++ only) Subscripting an array which has been declared @samp{register}. + +@item +(C++ only) Taking the address of a variable which has been declared @samp{register}. + +@item +(C++ only) A base class is not initialized in a derived class' copy constructor. +@c APPLE LOCAL end pod error 6089368 +@end itemize + +@item -Wno-div-by-zero +@opindex Wno-div-by-zero +@opindex Wdiv-by-zero +Do not warn about compile-time integer division by zero. Floating point +division by zero is not warned about, as it can be a legitimate way of +obtaining infinities and NaNs. + +@item -Wsystem-headers +@opindex Wsystem-headers +@cindex warnings from system headers +@cindex system headers, warnings from +Print warning messages for constructs found in system header files. +Warnings from system headers are normally suppressed, on the assumption +that they usually do not indicate real problems and would only make the +compiler output harder to read. Using this command line option tells +GCC to emit warnings from system headers as if they occurred in user +code. However, note that using @option{-Wall} in conjunction with this +option will @emph{not} warn about unknown pragmas in system +headers---for that, @option{-Wunknown-pragmas} must also be used. + +@item -Wfloat-equal +@opindex Wfloat-equal +Warn if floating point values are used in equality comparisons. + +The idea behind this is that sometimes it is convenient (for the +programmer) to consider floating-point values as approximations to +infinitely precise real numbers. If you are doing this, then you need +to compute (by analyzing the code, or in some other way) the maximum or +likely maximum error that the computation introduces, and allow for it +when performing comparisons (and when producing output, but that's a +different problem). In particular, instead of testing for equality, you +would check to see whether the two values have ranges that overlap; and +this is done with the relational operators, so equality comparisons are +probably mistaken. + +@c APPLE LOCAL begin -Wfour-char-constants +@item -Wfour-char-constants +@opindex Wfour-char-constants +Warn about four char constants, e.g. OSType 'APPL'. This warning is +disabled by default. +@c APPLE LOCAL end + +@item -Wtraditional @r{(C only)} +@opindex Wtraditional +Warn about certain constructs that behave differently in traditional and +ISO C@. Also warn about ISO C constructs that have no traditional C +equivalent, and/or problematic constructs which should be avoided. + +@itemize @bullet +@item +Macro parameters that appear within string literals in the macro body. +In traditional C macro replacement takes place within string literals, +but does not in ISO C@. + +@item +In traditional C, some preprocessor directives did not exist. +Traditional preprocessors would only consider a line to be a directive +if the @samp{#} appeared in column 1 on the line. Therefore +@option{-Wtraditional} warns about directives that traditional C +understands but would ignore because the @samp{#} does not appear as the +first character on the line. It also suggests you hide directives like +@samp{#pragma} not understood by traditional C by indenting them. Some +traditional implementations would not recognize @samp{#elif}, so it +suggests avoiding it altogether. + +@item +A function-like macro that appears without arguments. + +@item +The unary plus operator. + +@item +The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point +constant suffixes. (Traditional C does support the @samp{L} suffix on integer +constants.) Note, these suffixes appear in macros defined in the system +headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. +Use of these macros in user code might normally lead to spurious +warnings, however GCC's integrated preprocessor has enough context to +avoid warning in these cases. + +@item +A function declared external in one block and then used after the end of +the block. + +@item +A @code{switch} statement has an operand of type @code{long}. + +@item +A non-@code{static} function declaration follows a @code{static} one. +This construct is not accepted by some traditional C compilers. + +@item +The ISO type of an integer constant has a different width or +signedness from its traditional type. This warning is only issued if +the base of the constant is ten. I.e.@: hexadecimal or octal values, which +typically represent bit patterns, are not warned about. + +@item +Usage of ISO string concatenation is detected. + +@item +Initialization of automatic aggregates. + +@item +Identifier conflicts with labels. Traditional C lacks a separate +namespace for labels. + +@item +Initialization of unions. If the initializer is zero, the warning is +omitted. This is done under the assumption that the zero initializer in +user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing +initializer warnings and relies on default initialization to zero in the +traditional C case. + +@item +Conversions by prototypes between fixed/floating point values and vice +versa. The absence of these prototypes when compiling with traditional +C would cause serious problems. This is a subset of the possible +conversion warnings, for the full set use @option{-Wconversion}. + +@item +Use of ISO C style function definitions. This warning intentionally is +@emph{not} issued for prototype declarations or variadic functions +because these ISO C features will appear in your code when using +libiberty's traditional C compatibility macros, @code{PARAMS} and +@code{VPARAMS}. This warning is also bypassed for nested functions +because that feature is already a GCC extension and thus not relevant to +traditional C compatibility. +@end itemize + +@item -Wdeclaration-after-statement @r{(C only)} +@opindex Wdeclaration-after-statement +Warn when a declaration is found after a statement in a block. This +construct, known from C++, was introduced with ISO C99 and is by default +allowed in GCC@. It is not supported by ISO C90 and was not supported by +GCC versions before GCC 3.0. @xref{Mixed Declarations}. + +@c APPLE LOCAL begin -Wdiscard-qual 4086969 +@item -Wno-discard-qual +@opindex Wno-discard-qual +This flag allows user to suppress warning that is issued when qualification +is discarded in situations like, initialization, assignment and argument +passing. +@c APPLE LOCAL end -Wdiscard-qual 4086969 + +@item -Wundef +@opindex Wundef +Warn if an undefined identifier is evaluated in an @samp{#if} directive. + +@item -Wno-endif-labels +@opindex Wno-endif-labels +@opindex Wendif-labels +Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text. + +@item -Wshadow +@opindex Wshadow +Warn whenever a local variable shadows another local variable, parameter or +global variable or whenever a built-in function is shadowed. + +@item -Wlarger-than-@var{len} +@opindex Wlarger-than +Warn whenever an object of larger than @var{len} bytes is defined. + +@item -Wunsafe-loop-optimizations +@opindex Wunsafe-loop-optimizations +Warn if the loop cannot be optimized because the compiler could not +assume anything on the bounds of the loop indices. With +@option{-funsafe-loop-optimizations} warn if the compiler made +such assumptions. + +@item -Wpointer-arith +@opindex Wpointer-arith +Warn about anything that depends on the ``size of'' a function type or +of @code{void}. GNU C assigns these types a size of 1, for +convenience in calculations with @code{void *} pointers and pointers +to functions. + +@item -Wbad-function-cast @r{(C only)} +@opindex Wbad-function-cast +Warn whenever a function call is cast to a non-matching type. +For example, warn if @code{int malloc()} is cast to @code{anything *}. + +@item -Wc++-compat +Warn about ISO C constructs that are outside of the common subset of +ISO C and ISO C++, e.g.@: request for implicit conversion from +@code{void *} to a pointer to non-@code{void} type. + +@item -Wcast-qual +@opindex Wcast-qual +Warn whenever a pointer is cast so as to remove a type qualifier from +the target type. For example, warn if a @code{const char *} is cast +to an ordinary @code{char *}. + +@item -Wcast-align +@opindex Wcast-align +Warn whenever a pointer is cast such that the required alignment of the +target is increased. For example, warn if a @code{char *} is cast to +an @code{int *} on machines where integers can only be accessed at +two- or four-byte boundaries. + +@item -Wwrite-strings +@opindex Wwrite-strings +When compiling C, give string constants the type @code{const +char[@var{length}]} so that +copying the address of one into a non-@code{const} @code{char *} +pointer will get a warning; when compiling C++, warn about the +deprecated conversion from string literals to @code{char *}. This +warning, by default, is enabled for C++ programs. +These warnings will help you find at +compile time code that can try to write into a string constant, but +only if you have been very careful about using @code{const} in +declarations and prototypes. Otherwise, it will just be a nuisance; +this is why we did not make @option{-Wall} request these warnings. + +@item -Wconversion +@opindex Wconversion +Warn if a prototype causes a type conversion that is different from what +would happen to the same argument in the absence of a prototype. This +includes conversions of fixed point to floating and vice versa, and +conversions changing the width or signedness of a fixed point argument +except when the same as the default promotion. + +Also, warn if a negative integer constant expression is implicitly +converted to an unsigned type. For example, warn about the assignment +@code{x = -1} if @code{x} is unsigned. But do not warn about explicit +casts like @code{(unsigned) -1}. + +@c APPLE LOCAL begin mainline +@item -Wshorten-64-to-32 +@opindex Wshorten-64-to-32 +Warn if a value is implicitly converted from a 64 bit type to a 32 bit type. +@c APPLE LOCAL end mainline + +@c APPLE LOCAL begin mainline +@item -Wempty-body +@opindex Wempty-body +Warn if an empty body occurs in an @samp{if} or @samp{else} +statement. Additionally, in C++, warn when an empty body occurs +in a @samp{while} or @samp{for} statement with no whitespacing before +the semicolon. This warning is also enabled by @option{-Wextra}. +@c APPLE LOCAL end mainline + +@item -Wsign-compare +@opindex Wsign-compare +@cindex warning for comparison of signed and unsigned values +@cindex comparison of signed and unsigned values, warning +@cindex signed and unsigned values, comparison warning +Warn when a comparison between signed and unsigned values could produce +an incorrect result when the signed value is converted to unsigned. +This warning is also enabled by @option{-Wextra}; to get the other warnings +of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}. + +@item -Waddress +@opindex Waddress +@opindex Wno-address +Warn about suspicious uses of memory addresses. These include using +the address of a function in a conditional expression, such as +@code{void func(void); if (func)}, and comparisons against the memory +address of a string literal, such as @code{if (x == "abc")}. Such +uses typically indicate a programmer error: the address of a function +always evaluates to true, so their use in a conditional usually +indicate that the programmer forgot the parentheses in a function +call; and comparisons against string literals result in unspecified +behavior and are not portable in C, so they usually indicate that the +programmer intended to use @code{strcmp}. This warning is enabled by +@option{-Wall}. + +@item -Waggregate-return +@opindex Waggregate-return +Warn if any functions that return structures or unions are defined or +called. (In languages where you can return an array, this also elicits +a warning.) + +@item -Wno-attributes +@opindex Wno-attributes +@opindex Wattributes +Do not warn if an unexpected @code{__attribute__} is used, such as +unrecognized attributes, function attributes applied to variables, +etc. This will not stop errors for incorrect use of supported +attributes. + +@item -Wstrict-prototypes @r{(C only)} +@opindex Wstrict-prototypes +Warn if a function is declared or defined without specifying the +argument types. (An old-style function definition is permitted without +a warning if preceded by a declaration which specifies the argument +types.) + +@item -Wold-style-definition @r{(C only)} +@opindex Wold-style-definition +Warn if an old-style function definition is used. A warning is given +even if there is a previous prototype. + +@c APPLE LOCAL warn missing prototype 6261539 +@item -Wmissing-prototypes +@opindex Wmissing-prototypes +Warn if a global function is defined without a previous prototype +declaration. This warning is issued even if the definition itself +provides a prototype. The aim is to detect global functions that fail +to be declared in header files. + +@item -Wmissing-declarations @r{(C only)} +@opindex Wmissing-declarations +Warn if a global function is defined without a previous declaration. +Do so even if the definition itself provides a prototype. +Use this option to detect global functions that are not declared in +header files. + +@item -Wmissing-field-initializers +@opindex Wmissing-field-initializers +@opindex W +@opindex Wextra +Warn if a structure's initializer has some fields missing. For +example, the following code would cause such a warning, because +@code{x.h} is implicitly zero: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ 3, 4 @}; +@end smallexample + +This option does not warn about designated initializers, so the following +modification would not trigger a warning: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ .f = 3, .g = 4 @}; +@end smallexample + +This warning is included in @option{-Wextra}. To get other @option{-Wextra} +warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}. + +@item -Wmissing-noreturn +@opindex Wmissing-noreturn +Warn about functions which might be candidates for attribute @code{noreturn}. +Note these are only possible candidates, not absolute ones. Care should +be taken to manually verify functions actually do not ever return before +adding the @code{noreturn} attribute, otherwise subtle code generation +bugs could be introduced. You will not get a warning for @code{main} in +hosted C environments. + +@item -Wmissing-format-attribute +@opindex Wmissing-format-attribute +@opindex Wformat +Warn about function pointers which might be candidates for @code{format} +attributes. Note these are only possible candidates, not absolute ones. +GCC will guess that function pointers with @code{format} attributes that +are used in assignment, initialization, parameter passing or return +statements should have a corresponding @code{format} attribute in the +resulting type. I.e.@: the left-hand side of the assignment or +initialization, the type of the parameter variable, or the return type +of the containing function respectively should also have a @code{format} +attribute to avoid the warning. + +GCC will also warn about function definitions which might be +candidates for @code{format} attributes. Again, these are only +possible candidates. GCC will guess that @code{format} attributes +might be appropriate for any function that calls a function like +@code{vprintf} or @code{vscanf}, but this might not always be the +case, and some functions for which @code{format} attributes are +appropriate may not be detected. + +@item -Wno-multichar +@opindex Wno-multichar +@opindex Wmultichar +@c APPLE LOCAL begin -Wfour-char-constants +Do not warn if a multicharacter constant (@samp{'FOO'}) is used. +Usually they indicate a typo in the user's code, as they have +implementation-defined values, and should not be used in portable code. +This flag does not control warning for a constant with four characters, +use -Wfour-char-constants instead. +@c APPLE LOCAL end -Wfour-char-constants + +@item -Wnormalized=<none|id|nfc|nfkc> +@opindex Wnormalized +@cindex NFC +@cindex NFKC +@cindex character set, input normalization +In ISO C and ISO C++, two identifiers are different if they are +different sequences of characters. However, sometimes when characters +outside the basic ASCII character set are used, you can have two +different character sequences that look the same. To avoid confusion, +the ISO 10646 standard sets out some @dfn{normalization rules} which +when applied ensure that two sequences that look the same are turned into +the same sequence. GCC can warn you if you are using identifiers which +have not been normalized; this option controls that warning. + +There are four levels of warning that GCC supports. The default is +@option{-Wnormalized=nfc}, which warns about any identifier which is +not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the +recommended form for most uses. + +Unfortunately, there are some characters which ISO C and ISO C++ allow +in identifiers that when turned into NFC aren't allowable as +identifiers. That is, there's no way to use these symbols in portable +ISO C or C++ and have all your identifiers in NFC. +@option{-Wnormalized=id} suppresses the warning for these characters. +It is hoped that future versions of the standards involved will correct +this, which is why this option is not the default. + +You can switch the warning off for all characters by writing +@option{-Wnormalized=none}. You would only want to do this if you +were using some other normalization scheme (like ``D''), because +otherwise you can easily create bugs that are literally impossible to see. + +Some characters in ISO 10646 have distinct meanings but look identical +in some fonts or display methodologies, especially once formatting has +been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL +LETTER N'', will display just like a regular @code{n} which has been +placed in a superscript. ISO 10646 defines the @dfn{NFKC} +normalization scheme to convert all these into a standard form as +well, and GCC will warn if your code is not in NFKC if you use +@option{-Wnormalized=nfkc}. This warning is comparable to warning +about every identifier that contains the letter O because it might be +confused with the digit 0, and so is not the default, but may be +useful as a local coding convention if the programming environment is +unable to be fixed to display these characters distinctly. + +@item -Wno-deprecated-declarations +@opindex Wno-deprecated-declarations +Do not warn about uses of functions (@pxref{Function Attributes}), +variables (@pxref{Variable Attributes}), and types (@pxref{Type +Attributes}) marked as deprecated by using the @code{deprecated} +attribute. + +@item -Wno-overflow +@opindex Wno-overflow +Do not warn about compile-time overflow in constant expressions. + +@item -Woverride-init +@opindex Woverride-init +@opindex W +@opindex Wextra +Warn if an initialized field without side effects is overridden when +using designated initializers (@pxref{Designated Inits, , Designated +Initializers}). + +This warning is included in @option{-Wextra}. To get other +@option{-Wextra} warnings without this one, use @samp{-Wextra +-Wno-override-init}. + +@item -Wpacked +@opindex Wpacked +Warn if a structure is given the packed attribute, but the packed +attribute has no effect on the layout or size of the structure. +Such structures may be mis-aligned for little benefit. For +instance, in this code, the variable @code{f.x} in @code{struct bar} +will be misaligned even though @code{struct bar} does not itself +have the packed attribute: + +@smallexample +@group +struct foo @{ + int x; + char a, b, c, d; +@} __attribute__((packed)); +struct bar @{ + char z; + struct foo f; +@}; +@end group +@end smallexample + +@item -Wpadded +@opindex Wpadded +Warn if padding is included in a structure, either to align an element +of the structure or to align the whole structure. Sometimes when this +happens it is possible to rearrange the fields of the structure to +reduce the padding and so make the structure smaller. + +@item -Wredundant-decls +@opindex Wredundant-decls +Warn if anything is declared more than once in the same scope, even in +cases where multiple declaration is valid and changes nothing. + +@item -Wnested-externs @r{(C only)} +@opindex Wnested-externs +Warn if an @code{extern} declaration is encountered within a function. + +@item -Wunreachable-code +@opindex Wunreachable-code +Warn if the compiler detects that code will never be executed. + +This option is intended to warn when the compiler detects that at +least a whole line of source code will never be executed, because +some condition is never satisfied or because it is after a +procedure that never returns. + +It is possible for this option to produce a warning even though there +are circumstances under which part of the affected line can be executed, +so care should be taken when removing apparently-unreachable code. + +For instance, when a function is inlined, a warning may mean that the +line is unreachable in only one inlined copy of the function. + +This option is not made part of @option{-Wall} because in a debugging +version of a program there is often substantial code which checks +correct functioning of the program and is, hopefully, unreachable +because the program does work. Another common use of unreachable +code is to provide behavior which is selectable at compile-time. + +@item -Winline +@opindex Winline +Warn if a function can not be inlined and it was declared as inline. +Even with this option, the compiler will not warn about failures to +inline functions declared in system headers. + +The compiler uses a variety of heuristics to determine whether or not +to inline a function. For example, the compiler takes into account +the size of the function being inlined and the amount of inlining +that has already been done in the current function. Therefore, +seemingly insignificant changes in the source program can cause the +warnings produced by @option{-Winline} to appear or disappear. + +@item -Wno-invalid-offsetof @r{(C++ only)} +@opindex Wno-invalid-offsetof +Suppress warnings from applying the @samp{offsetof} macro to a non-POD +type. According to the 1998 ISO C++ standard, applying @samp{offsetof} +to a non-POD type is undefined. In existing C++ implementations, +however, @samp{offsetof} typically gives meaningful results even when +applied to certain kinds of non-POD types. (Such as a simple +@samp{struct} that fails to be a POD type only by virtue of having a +constructor.) This flag is for users who are aware that they are +writing nonportable code and who have deliberately chosen to ignore the +warning about it. + +The restrictions on @samp{offsetof} may be relaxed in a future version +of the C++ standard. + +@item -Wno-int-to-pointer-cast @r{(C only)} +@opindex Wno-int-to-pointer-cast +Suppress warnings from casts to pointer type of an integer of a +different size. + +@item -Wno-pointer-to-int-cast @r{(C only)} +@opindex Wno-pointer-to-int-cast +Suppress warnings from casts from a pointer to an integer type of a +different size. + +@item -Winvalid-pch +@opindex Winvalid-pch +Warn if a precompiled header (@pxref{Precompiled Headers}) is found in +the search path but can't be used. + +@item -Wlong-long +@opindex Wlong-long +@opindex Wno-long-long +Warn if @samp{long long} type is used. This is default. To inhibit +the warning messages, use @option{-Wno-long-long}. Flags +@option{-Wlong-long} and @option{-Wno-long-long} are taken into account +only when @option{-pedantic} flag is used. + +@item -Wvariadic-macros +@opindex Wvariadic-macros +@opindex Wno-variadic-macros +Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU +alternate syntax when in pedantic ISO C99 mode. This is default. +To inhibit the warning messages, use @option{-Wno-variadic-macros}. + +@item -Wvolatile-register-var +@opindex Wvolatile-register-var +@opindex Wno-volatile-register-var +Warn if a register variable is declared volatile. The volatile +modifier does not inhibit all optimizations that may eliminate reads +and/or writes to register variables. + +@item -Wdisabled-optimization +@opindex Wdisabled-optimization +Warn if a requested optimization pass is disabled. This warning does +not generally indicate that there is anything wrong with your code; it +merely indicates that GCC's optimizers were unable to handle the code +effectively. Often, the problem is that your code is too big or too +complex; GCC will refuse to optimize programs when the optimization +itself is likely to take inordinate amounts of time. + +@item -Wpointer-sign +@opindex Wpointer-sign +@opindex Wno-pointer-sign +Warn for pointer argument passing or assignment with different signedness. +This option is only supported for C and Objective-C@. It is implied by +@option{-Wall} and by @option{-pedantic}, which can be disabled with +@option{-Wno-pointer-sign}. + +@item -Werror +@opindex Werror +Make all warnings into errors. + +@item -Werror= +@opindex Werror= +Make the specified warning into an errors. The specifier for a +warning is appended, for example @option{-Werror=switch} turns the +warnings controlled by @option{-Wswitch} into errors. This switch +takes a negative form, to be used to negate @option{-Werror} for +specific warnings, for example @option{-Wno-error=switch} makes +@option{-Wswitch} warnings not be errors, even when @option{-Werror} +is in effect. You can use the @option{-fdiagnostics-show-option} +option to have each controllable warning amended with the option which +controls it, to determine what to use with this option. + +Note that specifying @option{-Werror=}@var{foo} automatically implies +@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not +imply anything. + +@item -Wstack-protector +@opindex Wstack-protector +This option is only active when @option{-fstack-protector} is active. It +warns about functions that will not be protected against stack smashing. + +@item -Woverlength-strings +@opindex Woverlength-strings +Warn about string constants which are longer than the ``minimum +maximum'' length specified in the C standard. Modern compilers +generally allow string constants which are much longer than the +standard's minimum limit, but very portable programs should avoid +using longer strings. + +The limit applies @emph{after} string constant concatenation, and does +not count the trailing NUL@. In C89, the limit was 509 characters; in +C99, it was raised to 4095. C++98 does not specify a normative +minimum maximum, so we do not diagnose overlength strings in C++@. + +This option is implied by @option{-pedantic}, and can be disabled with +@option{-Wno-overlength-strings}. +@end table + +@node Debugging Options +@section Options for Debugging Your Program or GCC +@cindex options, debugging +@cindex debugging information options + +GCC has various special options that are used for debugging +either your program or GCC: + +@table @gcctabopt +@item -g +@opindex g +Produce debugging information in the operating system's native format +(stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging +information. + +On most systems that use stabs format, @option{-g} enables use of extra +debugging information that only GDB can use; this extra information +makes debugging work better in GDB but will probably make other debuggers +crash or +refuse to read the program. If you want to control for certain whether +@c APPLE LOCAL begin prune man page +to generate the extra information, use @option{-gstabs+} or @option{-gstabs} +(see below). +@c APPLE LOCAL end prune man page + +GCC allows you to use @option{-g} with +@option{-O}. The shortcuts taken by optimized code may occasionally +produce surprising results: some variables you declared may not exist +at all; flow of control may briefly move where you did not expect it; +some statements may not be executed because they compute constant +results or their values were already at hand; some statements may +execute in different places because they were moved out of loops. + +Nevertheless it proves possible to debug optimized output. This makes +it reasonable to use the optimizer for programs that might have bugs. + +The following options are useful when GCC is generated with the +capability for more than one debugging format. + +@item -ggdb +@opindex ggdb +Produce debugging information for use by GDB@. This means to use the +most expressive format available (DWARF 2, stabs, or the native format +if neither of those are supported), including GDB extensions if at all +possible. + +@item -gstabs +@opindex gstabs +Produce debugging information in stabs format (if that is supported), +without GDB extensions. This is the format used by DBX on most BSD +systems. On MIPS, Alpha and System V Release 4 systems this option +produces stabs debugging output which is not understood by DBX or SDB@. +On System V Release 4 systems this option requires the GNU assembler. + +@c APPLE LOCAL begin 4167759 +@item -flimit-debug-info +@opindex -flimit-debug-info +Limit debug information produced to reduce size of debug binary. +@c APPLE LOCAL end 4167759 + +@item -feliminate-unused-debug-symbols +@opindex feliminate-unused-debug-symbols +Produce debugging information in stabs format (if that is supported), +for only symbols that are actually used. + +@item -femit-class-debug-always +Instead of emitting debugging information for a C++ class in only one +object file, emit it in all object files using the class. This option +should be used only with debuggers that are unable to handle the way GCC +normally emits debugging information for classes because using this +option will increase the size of debugging information by as much as a +factor of two. + +@item -gstabs+ +@opindex gstabs+ +Produce debugging information in stabs format (if that is supported), +using GNU extensions understood only by the GNU debugger (GDB)@. The +use of these extensions is likely to make other debuggers crash or +refuse to read the program. + +@c APPLE LOCAL prune man page +@ignore +@item -gcoff +@opindex gcoff +Produce debugging information in COFF format (if that is supported). +This is the format used by SDB on most System V systems prior to +System V Release 4. + +@item -gxcoff +@opindex gxcoff +Produce debugging information in XCOFF format (if that is supported). +This is the format used by the DBX debugger on IBM RS/6000 systems. + +@item -gxcoff+ +@opindex gxcoff+ +Produce debugging information in XCOFF format (if that is supported), +using GNU extensions understood only by the GNU debugger (GDB)@. The +use of these extensions is likely to make other debuggers crash or +refuse to read the program, and may cause assemblers other than the GNU +assembler (GAS) to fail with an error. +@c APPLE LOCAL prune man page +@end ignore + +@item -gdwarf-2 +@opindex gdwarf-2 +Produce debugging information in DWARF version 2 format (if that is +supported). This is the format used by DBX on IRIX 6. With this +option, GCC uses features of DWARF version 3 when they are useful; +version 3 is upward compatible with version 2, but may still cause +problems for older debuggers. + +@c APPLE LOCAL begin prune man page +(Other debug formats, such as @option{-gcoff}, are not supported in +Darwin or Mac OS X.) +@ignore +@item -gvms +@opindex gvms +Produce debugging information in VMS debug format (if that is +supported). This is the format used by DEBUG on VMS systems. +@end ignore +@c APPLE LOCAL end prune man page + +@item -g@var{level} +@itemx -ggdb@var{level} +@itemx -gstabs@var{level} +@c APPLE LOCAL prune man page +@ignore +@itemx -gcoff@var{level} +@itemx -gxcoff@var{level} +@itemx -gvms@var{level} +@c APPLE LOCAL prune man page +@end ignore +Request debugging information and also use @var{level} to specify how +much information. The default level is 2. + +@c APPLE LOCAL begin mainline 4.3 2006-12-20 4869554 +Level 0 produces no debug information at all. Thus, @option{-g0} negates +@option{-g}. +@c APPLE LOCAL end mainline 4.3 2006-12-20 4869554 + +Level 1 produces minimal information, enough for making backtraces in +parts of the program that you don't plan to debug. This includes +descriptions of functions and external variables, but no information +about local variables and no line numbers. + +Level 3 includes extra information, such as all the macro definitions +present in the program. Some debuggers support macro expansion when +you use @option{-g3}. + +@option{-gdwarf-2} does not accept a concatenated debug level, because +GCC used to support an option @option{-gdwarf} that meant to generate +debug information in version 1 of the DWARF format (which is very +different from version 2), and it would have been too confusing. That +debug format is long obsolete, but the option cannot be changed now. +Instead use an additional @option{-g@var{level}} option to change the +debug level for DWARF2. + +@item -feliminate-dwarf2-dups +@opindex feliminate-dwarf2-dups +Compress DWARF2 debugging information by eliminating duplicated +information about each symbol. This option only makes sense when +generating DWARF2 debugging information with @option{-gdwarf-2}. + +@cindex @command{prof} +@item -p +@opindex p +Generate extra code to write profile information suitable for the +analysis program @command{prof}. You must use this option when compiling +the source files you want data about, and you must also use it when +linking. + +@cindex @command{gprof} +@item -pg +@opindex pg +Generate extra code to write profile information suitable for the +analysis program @command{gprof}. You must use this option when compiling +the source files you want data about, and you must also use it when +linking. + +@item -Q +@opindex Q +Makes the compiler print out each function name as it is compiled, and +print some statistics about each pass when it finishes. + +@item -ftime-report +@opindex ftime-report +Makes the compiler print some statistics about the time consumed by each +pass when it finishes. + +@item -fmem-report +@opindex fmem-report +Makes the compiler print some statistics about permanent memory +allocation when it finishes. + +@c APPLE LOCAL begin opt diary +@item -fopt-diary +@opindex fopt-diary +Enable optimization diary entries using DWARF encoding. This option +does nothing unless @option{gdwarf-2} is specified. +@c APPLE LOCAL end opt diary +@item -fprofile-arcs +@opindex fprofile-arcs +Add code so that program flow @dfn{arcs} are instrumented. During +execution the program records how many times each branch and call is +executed and how many times it is taken or returns. When the compiled +program exits it saves this data to a file called +@file{@var{auxname}.gcda} for each source file. The data may be used for +profile-directed optimizations (@option{-fbranch-probabilities}), or for +test coverage analysis (@option{-ftest-coverage}). Each object file's +@var{auxname} is generated from the name of the output file, if +explicitly specified and it is not the final executable, otherwise it is +the basename of the source file. In both cases any suffix is removed +(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or +@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). +@xref{Cross-profiling}. + +@cindex @command{gcov} +@item --coverage +@opindex coverage + +This option is used to compile and link code instrumented for coverage +analysis. The option is a synonym for @option{-fprofile-arcs} +@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when +linking). See the documentation for those options for more details. + +@itemize + +@item +Compile the source files with @option{-fprofile-arcs} plus optimization +and code generation options. For test coverage analysis, use the +additional @option{-ftest-coverage} option. You do not need to profile +every source file in a program. + +@item +Link your object files with @option{-lgcov} or @option{-fprofile-arcs} +(the latter implies the former). + +@item +Run the program on a representative workload to generate the arc profile +information. This may be repeated any number of times. You can run +concurrent instances of your program, and provided that the file system +supports locking, the data files will be correctly updated. Also +@code{fork} calls are detected and correctly handled (double counting +will not happen). + +@item +For profile-directed optimizations, compile the source files again with +the same optimization and code generation options plus +@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that +Control Optimization}). + +@item +For test coverage analysis, use @command{gcov} to produce human readable +information from the @file{.gcno} and @file{.gcda} files. Refer to the +@command{gcov} documentation for further information. + +@end itemize + +With @option{-fprofile-arcs}, for each function of your program GCC +creates a program flow graph, then finds a spanning tree for the graph. +Only arcs that are not on the spanning tree have to be instrumented: the +compiler adds code to count the number of times that these arcs are +executed. When an arc is the only exit or only entrance to a block, the +instrumentation code can be added to the block; otherwise, a new basic +block must be created to hold the instrumentation code. + +@need 2000 +@item -ftest-coverage +@opindex ftest-coverage +Produce a notes file that the @command{gcov} code-coverage utility +(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to +show program coverage. Each source file's note file is called +@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option +above for a description of @var{auxname} and instructions on how to +generate test coverage data. Coverage data will match the source files +more closely, if you do not optimize. + +@c APPLE LOCAL begin mainline +@item -d@var{letters} +@item -fdump-rtl-@var{pass} +@opindex d +Says to make debugging dumps during compilation at times specified by +@var{letters}. This is used for debugging the RTL-based passes of the +compiler. The file names for most of the dumps are made by appending a +pass number and a word to the @var{dumpname}. @var{dumpname} is generated +from the name of the output file, if explicitly specified and it is not +an executable, otherwise it is the basename of the source file. These +switches may have different effects when @option{-E} is used for +preprocessing. +@c APPLE LOCAL end mainline + +Most debug dumps can be enabled either passing a letter to the @option{-d} +option, or with a long @option{-fdump-rtl} switch; here are the possible +letters for use in @var{letters} and @var{pass}, and their meanings: + +@table @gcctabopt +@item -dA +@opindex dA +Annotate the assembler output with miscellaneous debugging information. + +@item -dB +@itemx -fdump-rtl-bbro +@opindex dB +@opindex fdump-rtl-bbro +Dump after block reordering, to @file{@var{file}.148r.bbro}. + +@item -dc +@itemx -fdump-rtl-combine +@opindex dc +@opindex fdump-rtl-combine +Dump after instruction combination, to the file @file{@var{file}.129r.combine}. + +@item -dC +@itemx -fdump-rtl-ce1 +@itemx -fdump-rtl-ce2 +@opindex dC +@opindex fdump-rtl-ce1 +@opindex fdump-rtl-ce2 +@option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the +first if conversion, to the file @file{@var{file}.117r.ce1}. @option{-dC} +and @option{-fdump-rtl-ce2} enable dumping after the second if +conversion, to the file @file{@var{file}.130r.ce2}. + +@item -dd +@itemx -fdump-rtl-btl +@itemx -fdump-rtl-dbr +@opindex dd +@opindex fdump-rtl-btl +@opindex fdump-rtl-dbr +@option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch +target load optimization, to @file{@var{file}.31.btl}. @option{-dd} +and @option{-fdump-rtl-dbr} enable dumping after delayed branch +scheduling, to @file{@var{file}.36.dbr}. + +@item -dD +@opindex dD +Dump all macro definitions, at the end of preprocessing, in addition to +normal output. + +@item -dE +@itemx -fdump-rtl-ce3 +@opindex dE +@opindex fdump-rtl-ce3 +Dump after the third if conversion, to @file{@var{file}.146r.ce3}. + +@item -df +@itemx -fdump-rtl-cfg +@itemx -fdump-rtl-life +@opindex df +@opindex fdump-rtl-cfg +@opindex fdump-rtl-life +@option{-df} and @option{-fdump-rtl-cfg} enable dumping after control +and data flow analysis, to @file{@var{file}.116r.cfg}. @option{-df} +and @option{-fdump-rtl-cfg} enable dumping dump after life analysis, +to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}. + +@item -dg +@itemx -fdump-rtl-greg +@opindex dg +@opindex fdump-rtl-greg +Dump after global register allocation, to @file{@var{file}.139r.greg}. + +@item -dG +@itemx -fdump-rtl-gcse +@itemx -fdump-rtl-bypass +@opindex dG +@opindex fdump-rtl-gcse +@opindex fdump-rtl-bypass +@option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to +@file{@var{file}.114r.gcse}. @option{-dG} and @option{-fdump-rtl-bypass} +enable dumping after jump bypassing and control flow optimizations, to +@file{@var{file}.115r.bypass}. + +@item -dh +@itemx -fdump-rtl-eh +@opindex dh +@opindex fdump-rtl-eh +Dump after finalization of EH handling code, to @file{@var{file}.02.eh}. + +@item -di +@itemx -fdump-rtl-sibling +@opindex di +@opindex fdump-rtl-sibling +Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}. + +@item -dj +@itemx -fdump-rtl-jump +@opindex dj +@opindex fdump-rtl-jump +Dump after the first jump optimization, to @file{@var{file}.112r.jump}. + +@item -dk +@itemx -fdump-rtl-stack +@opindex dk +@opindex fdump-rtl-stack +Dump after conversion from registers to stack, to @file{@var{file}.152r.stack}. + +@item -dl +@itemx -fdump-rtl-lreg +@opindex dl +@opindex fdump-rtl-lreg +Dump after local register allocation, to @file{@var{file}.138r.lreg}. + +@item -dL +@itemx -fdump-rtl-loop2 +@opindex dL +@opindex fdump-rtl-loop2 +@option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the +loop optimization pass, to @file{@var{file}.119r.loop2}, +@file{@var{file}.120r.loop2_init}, +@file{@var{file}.121r.loop2_invariant}, and +@file{@var{file}.125r.loop2_done}. + +@item -dm +@itemx -fdump-rtl-sms +@opindex dm +@opindex fdump-rtl-sms +Dump after modulo scheduling, to @file{@var{file}.136r.sms}. + +@item -dM +@itemx -fdump-rtl-mach +@opindex dM +@opindex fdump-rtl-mach +@c APPLE LOCAL begin mainline +Dump after performing the machine dependent reorganization pass, to +@file{@var{file}.155r.mach} if that pass exists. +@c APPLE LOCAL end mainline + +@item -dn +@itemx -fdump-rtl-rnreg +@opindex dn +@opindex fdump-rtl-rnreg +Dump after register renumbering, to @file{@var{file}.147r.rnreg}. + +@item -dN +@itemx -fdump-rtl-regmove +@opindex dN +@opindex fdump-rtl-regmove +Dump after the register move pass, to @file{@var{file}.132r.regmove}. + +@item -do +@itemx -fdump-rtl-postreload +@opindex do +@opindex fdump-rtl-postreload +Dump after post-reload optimizations, to @file{@var{file}.24.postreload}. + +@item -dr +@itemx -fdump-rtl-expand +@opindex dr +@opindex fdump-rtl-expand +Dump after RTL generation, to @file{@var{file}.104r.expand}. + +@item -dR +@itemx -fdump-rtl-sched2 +@opindex dR +@opindex fdump-rtl-sched2 +Dump after the second scheduling pass, to @file{@var{file}.150r.sched2}. + +@item -ds +@itemx -fdump-rtl-cse +@opindex ds +@opindex fdump-rtl-cse +Dump after CSE (including the jump optimization that sometimes follows +CSE), to @file{@var{file}.113r.cse}. + +@item -dS +@itemx -fdump-rtl-sched +@opindex dS +@opindex fdump-rtl-sched +Dump after the first scheduling pass, to @file{@var{file}.21.sched}. + +@item -dt +@itemx -fdump-rtl-cse2 +@opindex dt +@opindex fdump-rtl-cse2 +Dump after the second CSE pass (including the jump optimization that +sometimes follows CSE), to @file{@var{file}.127r.cse2}. + +@item -dT +@itemx -fdump-rtl-tracer +@opindex dT +@opindex fdump-rtl-tracer +Dump after running tracer, to @file{@var{file}.118r.tracer}. + +@item -dV +@itemx -fdump-rtl-vpt +@itemx -fdump-rtl-vartrack +@opindex dV +@opindex fdump-rtl-vpt +@opindex fdump-rtl-vartrack +@option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value +profile transformations, to @file{@var{file}.10.vpt}. @option{-dV} +and @option{-fdump-rtl-vartrack} enable dumping after variable tracking, +to @file{@var{file}.154r.vartrack}. + +@item -dw +@itemx -fdump-rtl-flow2 +@opindex dw +@opindex fdump-rtl-flow2 +Dump after the second flow pass, to @file{@var{file}.142r.flow2}. + +@item -dz +@itemx -fdump-rtl-peephole2 +@opindex dz +@opindex fdump-rtl-peephole2 +Dump after the peephole pass, to @file{@var{file}.145r.peephole2}. + +@item -dZ +@itemx -fdump-rtl-web +@opindex dZ +@opindex fdump-rtl-web +Dump after live range splitting, to @file{@var{file}.126r.web}. + +@item -da +@itemx -fdump-rtl-all +@opindex da +@opindex fdump-rtl-all +Produce all the dumps listed above. + +@item -dH +@opindex dH +Produce a core dump whenever an error occurs. + +@item -dm +@opindex dm +Print statistics on memory usage, at the end of the run, to +standard error. + +@item -dp +@opindex dp +Annotate the assembler output with a comment indicating which +pattern and alternative was used. The length of each instruction is +also printed. + +@item -dP +@opindex dP +Dump the RTL in the assembler output as a comment before each instruction. +Also turns on @option{-dp} annotation. + +@item -dv +@opindex dv +For each of the other indicated dump files (either with @option{-d} or +@option{-fdump-rtl-@var{pass}}), dump a representation of the control flow +graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}. + +@item -dx +@opindex dx +Just generate RTL for a function instead of compiling it. Usually used +with @samp{r} (@option{-fdump-rtl-expand}). + +@item -dy +@opindex dy +Dump debugging information during parsing, to standard error. +@end table + +@item -fdump-noaddr +@opindex fdump-noaddr +When doing debugging dumps (see @option{-d} option above), suppress +address output. This makes it more feasible to use diff on debugging +dumps for compiler invocations with different compiler binaries and/or +different text / bss / data / heap / stack / dso start locations. + +@item -fdump-unnumbered +@opindex fdump-unnumbered +When doing debugging dumps (see @option{-d} option above), suppress instruction +numbers, line number note and address output. This makes it more feasible to +use diff on debugging dumps for compiler invocations with different +options, in particular with and without @option{-g}. + +@item -fdump-translation-unit @r{(C++ only)} +@itemx -fdump-translation-unit-@var{options} @r{(C++ only)} +@opindex fdump-translation-unit +Dump a representation of the tree structure for the entire translation +unit to a file. The file name is made by appending @file{.tu} to the +source file name. If the @samp{-@var{options}} form is used, @var{options} +controls the details of the dump as described for the +@option{-fdump-tree} options. + +@item -fdump-class-hierarchy @r{(C++ only)} +@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} +@opindex fdump-class-hierarchy +Dump a representation of each class's hierarchy and virtual function +table layout to a file. The file name is made by appending @file{.class} +to the source file name. If the @samp{-@var{options}} form is used, +@var{options} controls the details of the dump as described for the +@option{-fdump-tree} options. + +@item -fdump-ipa-@var{switch} +@opindex fdump-ipa +Control the dumping at various stages of inter-procedural analysis +language tree to a file. The file name is generated by appending a switch +specific suffix to the source file name. The following dumps are possible: + +@table @samp +@item all +Enables all inter-procedural analysis dumps; currently the only produced +dump is the @samp{cgraph} dump. + +@item cgraph +Dumps information about call-graph optimization, unused function removal, +and inlining decisions. +@end table + +@item -fdump-tree-@var{switch} +@itemx -fdump-tree-@var{switch}-@var{options} +@opindex fdump-tree +Control the dumping at various stages of processing the intermediate +language tree to a file. The file name is generated by appending a switch +specific suffix to the source file name. If the @samp{-@var{options}} +form is used, @var{options} is a list of @samp{-} separated options that +control the details of the dump. Not all options are applicable to all +dumps, those which are not meaningful will be ignored. The following +options are available + +@table @samp +@item address +Print the address of each node. Usually this is not meaningful as it +changes according to the environment and source file. Its primary use +is for tying up a dump file with a debug environment. +@item slim +Inhibit dumping of members of a scope or body of a function merely +because that scope has been reached. Only dump such items when they +are directly reachable by some other path. When dumping pretty-printed +trees, this option inhibits dumping the bodies of control structures. +@item raw +Print a raw representation of the tree. By default, trees are +pretty-printed into a C-like representation. +@item details +Enable more detailed dumps (not honored by every dump option). +@item stats +Enable dumping various statistics about the pass (not honored by every dump +option). +@item blocks +Enable showing basic block boundaries (disabled in raw dumps). +@item vops +Enable showing virtual operands for every statement. +@item lineno +Enable showing line numbers for statements. +@item uid +Enable showing the unique ID (@code{DECL_UID}) for each variable. +@item all +Turn on all options, except @option{raw}, @option{slim} and @option{lineno}. +@end table + +The following tree dumps are possible: +@table @samp + +@item original +Dump before any tree based optimization, to @file{@var{file}.original}. + +@item optimized +Dump after all tree based optimization, to @file{@var{file}.optimized}. + +@item inlined +Dump after function inlining, to @file{@var{file}.inlined}. + +@item gimple +@opindex fdump-tree-gimple +Dump each function before and after the gimplification pass to a file. The +file name is made by appending @file{.gimple} to the source file name. + +@item cfg +@opindex fdump-tree-cfg +Dump the control flow graph of each function to a file. The file name is +made by appending @file{.cfg} to the source file name. + +@item vcg +@opindex fdump-tree-vcg +Dump the control flow graph of each function to a file in VCG format. The +file name is made by appending @file{.vcg} to the source file name. Note +that if the file contains more than one function, the generated file cannot +be used directly by VCG@. You will need to cut and paste each function's +graph into its own separate file first. + +@item ch +@opindex fdump-tree-ch +Dump each function after copying loop headers. The file name is made by +appending @file{.ch} to the source file name. + +@item ssa +@opindex fdump-tree-ssa +Dump SSA related information to a file. The file name is made by appending +@file{.ssa} to the source file name. + +@item salias +@opindex fdump-tree-salias +Dump structure aliasing variable information to a file. This file name +is made by appending @file{.salias} to the source file name. + +@item alias +@opindex fdump-tree-alias +Dump aliasing information for each function. The file name is made by +appending @file{.alias} to the source file name. + +@item ccp +@opindex fdump-tree-ccp +Dump each function after CCP@. The file name is made by appending +@file{.ccp} to the source file name. + +@item storeccp +@opindex fdump-tree-storeccp +Dump each function after STORE-CCP. The file name is made by appending +@file{.storeccp} to the source file name. + +@item pre +@opindex fdump-tree-pre +Dump trees after partial redundancy elimination. The file name is made +by appending @file{.pre} to the source file name. + +@item fre +@opindex fdump-tree-fre +Dump trees after full redundancy elimination. The file name is made +by appending @file{.fre} to the source file name. + +@item copyprop +@opindex fdump-tree-copyprop +Dump trees after copy propagation. The file name is made +by appending @file{.copyprop} to the source file name. + +@item store_copyprop +@opindex fdump-tree-store_copyprop +Dump trees after store copy-propagation. The file name is made +by appending @file{.store_copyprop} to the source file name. + +@item dce +@opindex fdump-tree-dce +Dump each function after dead code elimination. The file name is made by +appending @file{.dce} to the source file name. + +@item mudflap +@opindex fdump-tree-mudflap +Dump each function after adding mudflap instrumentation. The file name is +made by appending @file{.mudflap} to the source file name. + +@item sra +@opindex fdump-tree-sra +Dump each function after performing scalar replacement of aggregates. The +file name is made by appending @file{.sra} to the source file name. + +@item sink +@opindex fdump-tree-sink +Dump each function after performing code sinking. The file name is made +by appending @file{.sink} to the source file name. + +@item dom +@opindex fdump-tree-dom +Dump each function after applying dominator tree optimizations. The file +name is made by appending @file{.dom} to the source file name. + +@item dse +@opindex fdump-tree-dse +Dump each function after applying dead store elimination. The file +name is made by appending @file{.dse} to the source file name. + +@item phiopt +@opindex fdump-tree-phiopt +Dump each function after optimizing PHI nodes into straightline code. The file +name is made by appending @file{.phiopt} to the source file name. + +@item forwprop +@opindex fdump-tree-forwprop +Dump each function after forward propagating single use variables. The file +name is made by appending @file{.forwprop} to the source file name. + +@item copyrename +@opindex fdump-tree-copyrename +Dump each function after applying the copy rename optimization. The file +name is made by appending @file{.copyrename} to the source file name. + +@item nrv +@opindex fdump-tree-nrv +Dump each function after applying the named return value optimization on +generic trees. The file name is made by appending @file{.nrv} to the source +file name. + +@item vect +@opindex fdump-tree-vect +Dump each function after applying vectorization of loops. The file name is +made by appending @file{.vect} to the source file name. + +@item vrp +@opindex fdump-tree-vrp +Dump each function after Value Range Propagation (VRP). The file name +is made by appending @file{.vrp} to the source file name. + +@item all +@opindex fdump-tree-all +Enable all the available tree dumps with the flags provided in this option. +@end table + +@item -ftree-vectorizer-verbose=@var{n} +@opindex ftree-vectorizer-verbose +This option controls the amount of debugging output the vectorizer prints. +This information is written to standard error, unless +@option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified, +in which case it is output to the usual dump listing file, @file{.vect}. +For @var{n}=0 no diagnostic information is reported. +If @var{n}=1 the vectorizer reports each loop that got vectorized, +and the total number of loops that got vectorized. +If @var{n}=2 the vectorizer also reports non-vectorized loops that passed +the first analysis phase (vect_analyze_loop_form) - i.e. countable, +inner-most, single-bb, single-entry/exit loops. This is the same verbosity +level that @option{-fdump-tree-vect-stats} uses. +Higher verbosity levels mean either more information dumped for each +reported loop, or same amount of information reported for more loops: +If @var{n}=3, alignment related information is added to the reports. +If @var{n}=4, data-references related information (e.g. memory dependences, +memory access-patterns) is added to the reports. +If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops +that did not pass the first analysis phase (i.e. may not be countable, or +may have complicated control-flow). +If @var{n}=6, the vectorizer reports also non-vectorized nested loops. +For @var{n}=7, all the information the vectorizer generates during its +analysis and transformation is reported. This is the same verbosity level +that @option{-fdump-tree-vect-details} uses. + +@item -frandom-seed=@var{string} +@opindex frandom-string +This option provides a seed that GCC uses when it would otherwise use +random numbers. It is used to generate certain symbol names +that have to be different in every compiled file. It is also used to +place unique stamps in coverage data files and the object files that +produce them. You can use the @option{-frandom-seed} option to produce +reproducibly identical object files. + +The @var{string} should be different for every file you compile. + +@item -fsched-verbose=@var{n} +@opindex fsched-verbose +On targets that use instruction scheduling, this option controls the +amount of debugging output the scheduler prints. This information is +written to standard error, unless @option{-dS} or @option{-dR} is +specified, in which case it is output to the usual dump +listing file, @file{.sched} or @file{.sched2} respectively. However +for @var{n} greater than nine, the output is always printed to standard +error. + +For @var{n} greater than zero, @option{-fsched-verbose} outputs the +same information as @option{-dRS}. For @var{n} greater than one, it +also output basic block probabilities, detailed ready list information +and unit/insn info. For @var{n} greater than two, it includes RTL +at abort point, control-flow and regions info. And for @var{n} over +four, @option{-fsched-verbose} also includes dependence info. + +@item -save-temps +@opindex save-temps +Store the usual ``temporary'' intermediate files permanently; place them +in the current directory and name them based on the source file. Thus, +compiling @file{foo.c} with @samp{-c -save-temps} would produce files +@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a +preprocessed @file{foo.i} output file even though the compiler now +normally uses an integrated preprocessor. + +When used in combination with the @option{-x} command line option, +@option{-save-temps} is sensible enough to avoid over writing an +input source file with the same extension as an intermediate file. +The corresponding intermediate file may be obtained by renaming the +source file before using @option{-save-temps}. + +@item -time +@opindex time +Report the CPU time taken by each subprocess in the compilation +sequence. For C source files, this is the compiler proper and assembler +(plus the linker if linking is done). The output looks like this: + +@smallexample +# cc1 0.12 0.01 +# as 0.00 0.01 +@end smallexample + +The first number on each line is the ``user time'', that is time spent +executing the program itself. The second number is ``system time'', +time spent executing operating system routines on behalf of the program. +Both numbers are in seconds. + +@item -fvar-tracking +@opindex fvar-tracking +Run variable tracking pass. It computes where variables are stored at each +position in code. Better debugging information is then generated +(if the debugging information format supports this information). + +It is enabled by default when compiling with optimization (@option{-Os}, +@c APPLE LOCAL -Oz +@option{-O}, @option{-O2}, @option{-Oz} (APPLE ONLY), ...), debugging information (@option{-g}) and +the debug info format supports it. + +@item -print-file-name=@var{library} +@opindex print-file-name +Print the full absolute name of the library file @var{library} that +would be used when linking---and don't do anything else. With this +option, GCC does not compile or link anything; it just prints the +file name. + +@item -print-multi-directory +@opindex print-multi-directory +Print the directory name corresponding to the multilib selected by any +other switches present in the command line. This directory is supposed +to exist in @env{GCC_EXEC_PREFIX}. + +@item -print-multi-lib +@opindex print-multi-lib +Print the mapping from multilib directory names to compiler switches +that enable them. The directory name is separated from the switches by +@samp{;}, and each switch starts with an @samp{@@} instead of the +@samp{-}, without spaces between multiple switches. This is supposed to +ease shell-processing. + +@item -print-prog-name=@var{program} +@opindex print-prog-name +Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. + +@item -print-libgcc-file-name +@opindex print-libgcc-file-name +Same as @option{-print-file-name=libgcc.a}. + +This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} +but you do want to link with @file{libgcc.a}. You can do + +@smallexample +gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` +@end smallexample + +@item -print-search-dirs +@opindex print-search-dirs +Print the name of the configured installation directory and a list of +program and library directories @command{gcc} will search---and don't do anything else. + +This is useful when @command{gcc} prints the error message +@samp{installation problem, cannot exec cpp0: No such file or directory}. +To resolve this you either need to put @file{cpp0} and the other compiler +components where @command{gcc} expects to find them, or you can set the environment +variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. +Don't forget the trailing @samp{/}. +@xref{Environment Variables}. + +@item -dumpmachine +@opindex dumpmachine +Print the compiler's target machine (for example, +@samp{i686-pc-linux-gnu})---and don't do anything else. + +@item -dumpversion +@opindex dumpversion +Print the compiler version (for example, @samp{3.0})---and don't do +anything else. + +@item -dumpspecs +@opindex dumpspecs +Print the compiler's built-in specs---and don't do anything else. (This +is used when GCC itself is being built.) @xref{Spec Files}. + +@item -feliminate-unused-debug-types +@opindex feliminate-unused-debug-types +Normally, when producing DWARF2 output, GCC will emit debugging +information for all types declared in a compilation +unit, regardless of whether or not they are actually used +in that compilation unit. Sometimes this is useful, such as +if, in the debugger, you want to cast a value to a type that is +not actually used in your program (but is declared). More often, +however, this results in a significant amount of wasted space. +With this option, GCC will avoid producing debug symbol output +for types that are nowhere used in the source file being compiled. +@end table + +@node Optimize Options +@section Options That Control Optimization +@cindex optimize options +@cindex options, optimization + +These options control various sorts of optimizations. + +Without any optimization option, the compiler's goal is to reduce the +cost of compilation and to make debugging produce the expected +results. Statements are independent: if you stop the program with a +breakpoint between statements, you can then assign a new value to any +variable or change the program counter to any other statement in the +function and get exactly the results you would expect from the source +code. + +Turning on optimization flags makes the compiler attempt to improve +the performance and/or code size at the expense of compilation time +and possibly the ability to debug the program. + +The compiler performs optimization based on the knowledge it has of +the program. Optimization levels @option{-O} and above, in +particular, enable @emph{unit-at-a-time} mode, which allows the +compiler to consider information gained from later functions in +the file when compiling a function. Compiling multiple files at +once to a single output file in @emph{unit-at-a-time} mode allows +the compiler to use information gained from all of the files when +compiling each of them. + +Not all optimizations are controlled directly by a flag. Only +optimizations that have a flag are listed. + +@table @gcctabopt +@item -O +@itemx -O1 +@opindex O +@opindex O1 +Optimize. Optimizing compilation takes somewhat more time, and a lot +more memory for a large function. + +With @option{-O}, the compiler tries to reduce code size and execution +time, without performing any optimizations that take a great deal of +compilation time. + +@option{-O} turns on the following optimization flags: +@gccoptlist{-fdefer-pop @gol +-fdelayed-branch @gol +-fguess-branch-probability @gol +-fcprop-registers @gol +-fif-conversion @gol +-fif-conversion2 @gol +-ftree-ccp @gol +-ftree-dce @gol +-ftree-dominator-opts @gol +-ftree-dse @gol +-ftree-ter @gol +-ftree-lrs @gol +-ftree-sra @gol +-ftree-copyrename @gol +-ftree-fre @gol +-ftree-ch @gol +-funit-at-a-time @gol +-fmerge-constants} + +@option{-O} also turns on @option{-fomit-frame-pointer} on machines +where doing so does not interfere with debugging. + +@item -O2 +@opindex O2 +Optimize even more. GCC performs nearly all supported optimizations +that do not involve a space-speed tradeoff. The compiler does not +perform loop unrolling or function inlining when you specify @option{-O2}. +As compared to @option{-O}, this option increases both compilation time +and the performance of the generated code. + +@option{-O2} turns on all optimization flags specified by @option{-O}. It +also turns on the following optimization flags: +@gccoptlist{-fthread-jumps @gol +-fcrossjumping @gol +-foptimize-sibling-calls @gol +-fcse-follow-jumps -fcse-skip-blocks @gol +-fgcse -fgcse-lm @gol +-fexpensive-optimizations @gol +-frerun-cse-after-loop @gol +-fcaller-saves @gol +-fpeephole2 @gol +-fschedule-insns -fschedule-insns2 @gol +-fsched-interblock -fsched-spec @gol +-fregmove @gol +-fstrict-aliasing -fstrict-overflow @gol +-fdelete-null-pointer-checks @gol +-freorder-blocks -freorder-functions @gol +-falign-functions -falign-jumps @gol +-falign-loops -falign-labels @gol +-ftree-vrp @gol +-ftree-pre} + +Please note the warning under @option{-fgcse} about +invoking @option{-O2} on programs that use computed gotos. + +@option{-O2} doesn't turn on @option{-ftree-vrp} for the Ada compiler. +This option must be explicitly specified on the command line to be +enabled for the Ada compiler. + +@c APPLE LOCAL begin optimization +In Apple's version of GCC, @option{-fstrict-aliasing}, +@option{-freorder-blocks}, and @option{-fsched-interblock} +are disabled by default when optimizing. +@c APPLE LOCAL end optimization + +@item -O3 +@opindex O3 +Optimize yet more. @option{-O3} turns on all optimizations specified by +@option{-O2} and also turns on the @option{-finline-functions}, +@option{-funswitch-loops} and @option{-fgcse-after-reload} options. + +@item -O0 +@opindex O0 +Do not optimize. This is the default. + +@c APPLE LOCAL begin -fast or -fastf or -fastcp +@item -fast +@opindex fast +Optimize for maximum performance. @option{-fast} changes the overall optimization +strategy of GCC in order to produce the fastest possible running code for PPC7450 +and G5 architectures. By default, @option{-fast} optimizes for G5. Programs +optimized for G5 will not run on PPC7450. To optimize for PPC7450, add +@option{-mcpu=7450} on command line. + +@option{-fast} currently enables the following optimization flags (for G5 and PPC7450). +These flags may change in the future. You cannot override any of these options if you use +@option{-fast} except by setting @option{-mcpu=7450} (or @option{-fPIC}, see below). + +@gccoptlist{-O3 +-falign-loops-max-skip=15 +-falign-jumps-max-skip=15 +-falign-loops=16 +-falign-jumps=16 +-falign-functions=16 +-malign-natural (except when -fastf is specified) +-ffast-math +-fstrict-aliasing +-funroll-loops +-ftree-loop-linear +-ftree-loop-memset +-mcpu=G5 +-mpowerpc-gpopt +-mtune=G5 (unless -mtune=G4 is specified). +-fsched-interblock +-fgcse-sm +-mpowerpc64} + +To build shared libraries with @option{-fast}, specify @option{-fPIC} +on the command line as @option{-fast} turns on @option{-mdynamic-no-pic} +otherwise. + +Important notes: @option{-ffast-math} results in code that is not necessarily +IEEE-compliant. @option{-fstrict-aliasing} is highly likely to break +non-standard-compliant programs. @option{-malign-natural} only works properly if +the entire program is compiled with it, and none of the standard headers/libraries +contain any code that changes alignment when this option is used. + +On Intel target, @option{-fast} currently enables the following optimization flags: + +@gccoptlist{-O3 +-fomit-frame-pointer +-fstrict-aliasing +-momit-leaf-frame-pointer +-fno-tree-pre +-falign-loops} + +All choices of flags enabled by @option{-fast} are subject to change without notice. + +@c APPLE LOCAL end -fast or -fastf or -fastcp + +@c APPLE LOCAL begin 4231761 -Oz +@item -Os +@opindex Os +Optimize for size, but not at the expense of speed. +@option{-Os} enables all @option{-O2} optimizations that +do not typically increase code size. However, instructions +are chosen for best performance, regardless of size. +To optimize solely for size on Darwin, use @option{-Oz} (APPLE ONLY). + +The following options are set for @option{-O2}, but are disabled under @option{-Os}: +@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol +-falign-labels -freorder-blocks -freorder-blocks-and-partition @gol +-fprefetch-loop-arrays -ftree-vect-loop-version} + +@c APPLE LOCAL begin 4200438 +When optimizing with @option{-Os} or @option{-Oz} (APPLE ONLY) on +Darwin, any function up to 30 ``estimated insns'' in size will be +considered for inlining. When compiling C and Objective-C sourcefiles with +@option{-Os} or @option{-Oz} on Darwin, functions explictly marked +with the @code{inline} keyword up to 450 ``estimated insns'' in size +will be considered for inlining. +@c APPLE LOCAL end 4200438 +@c APPLE LOCAL begin Disable string insns with -Os on Darwin (radar 3509006) +When compiling for Apple POWERPC targets, @option{-Os} and +@option{-Oz} (APPLE ONLY) disable use of the string instructions even though they +would usually be smaller, because the kernel can't emulate them +correctly in some rare cases. This behavior is not portable to any +other gcc environment, and will not affect most programs at all. If +you really want the string instructions, use -mstring. +@c APPLE LOCAL end Disable string insns with -Os on Darwin (radar 3509006) + +@item -Oz +@opindex Oz +(APPLE ONLY) Optimize for size, regardless of performance. +@option{-Oz} enables the same optimization flags that @option{-Os} +uses, but @option{-Oz} also enables other optimizations intended solely +to reduce code size. In particular, instructions that encode into +fewer bytes are preferred over longer instructions that execute in +fewer cycles. @option{-Oz} on Darwin is very similar to @option{-Os} +in FSF distributions of GCC. @option{-Oz} employs the same inlining +limits and avoids string instructions just like @option{-Os}. +@c APPLE LOCAL end 4231761 -Oz + +If you use multiple @option{-O} options, with or without level numbers, +the last such option is the one that is effective. +@end table + +Options of the form @option{-f@var{flag}} specify machine-independent +flags. Most flags have both positive and negative forms; the negative +form of @option{-ffoo} would be @option{-fno-foo}. In the table +below, only one of the forms is listed---the one you typically will +use. You can figure out the other form by either removing @samp{no-} +or adding it. + +The following options control specific optimizations. They are either +activated by @option{-O} options or are related to ones that are. You +can use the following flags in the rare cases when ``fine-tuning'' of +optimizations to be performed is desired. + +@table @gcctabopt +@item -fno-default-inline +@opindex fno-default-inline +Do not make member functions inline by default merely because they are +defined inside the class scope (C++ only). Otherwise, when you specify +@w{@option{-O}}, member functions defined inside class scope are compiled +inline by default; i.e., you don't need to add @samp{inline} in front of +the member function name. + +@item -fno-defer-pop +@opindex fno-defer-pop +Always pop the arguments to each function call as soon as that function +returns. For machines which must pop arguments after a function call, +the compiler normally lets arguments accumulate on the stack for several +function calls and pops them all at once. + +@c APPLE LOCAL begin 4231761 -Oz +Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, +@option{-Oz} (APPLE ONLY). +@c APPLE LOCAL end 4231761 -Oz + +@item -fforce-mem +@opindex fforce-mem +Force memory operands to be copied into registers before doing +arithmetic on them. This produces better code by making all memory +references potential common subexpressions. When they are not common +subexpressions, instruction combination should eliminate the separate +register-load. This option is now a nop and will be removed in 4.3. + +@item -fforce-addr +@opindex fforce-addr +Force memory address constants to be copied into registers before +doing arithmetic on them. + +@item -fomit-frame-pointer +@opindex fomit-frame-pointer +Don't keep the frame pointer in a register for functions that +don't need one. This avoids the instructions to save, set up and +restore frame pointers; it also makes an extra register available +in many functions. @strong{It also makes debugging impossible on +some machines.} + +On some machines, such as the VAX, this flag has no effect, because +the standard calling sequence automatically handles the frame pointer +and nothing is saved by pretending it doesn't exist. The +machine-description macro @code{FRAME_POINTER_REQUIRED} controls +whether a target machine supports this flag. @xref{Registers,,Register +Usage, gccint, GNU Compiler Collection (GCC) Internals}. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -foptimize-sibling-calls +@opindex foptimize-sibling-calls +Optimize sibling and tail recursive calls. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fno-inline +@opindex fno-inline +Don't pay attention to the @code{inline} keyword. Normally this option +is used to keep the compiler from expanding any functions inline. +Note that if you are not optimizing, no functions can be expanded inline. + +@item -finline-functions +@opindex finline-functions +Integrate all simple functions into their callers. The compiler +heuristically decides which functions are simple enough to be worth +integrating in this way. + +If all calls to a given function are integrated, and the function is +declared @code{static}, then the function is normally not output as +assembler code in its own right. + +Enabled at level @option{-O3}. + +@item -finline-functions-called-once +@opindex finline-functions-called-once +Consider all @code{static} functions called once for inlining into their +caller even if they are not marked @code{inline}. If a call to a given +function is integrated, then the function is not output as assembler code +in its own right. + +Enabled if @option{-funit-at-a-time} is enabled. + +@item -fearly-inlining +@opindex fearly-inlining +Inline functions marked by @code{always_inline} and functions whose body seems +smaller than the function call overhead early before doing +@option{-fprofile-generate} instrumentation and real inlining pass. Doing so +makes profiling significantly cheaper and usually inlining faster on programs +having large chains of nested wrapper functions. + +Enabled by default. + +@item -finline-limit=@var{n} +@opindex finline-limit +By default, GCC limits the size of functions that can be inlined. This flag +allows the control of this limit for functions that are explicitly marked as +inline (i.e., marked with the inline keyword or defined within the class +definition in c++). @var{n} is the size of functions that can be inlined in +number of pseudo instructions (not counting parameter handling). The default +value of @var{n} is 600. +Increasing this value can result in more inlined code at +the cost of compilation time and memory consumption. Decreasing usually makes +the compilation faster and less code will be inlined (which presumably +means slower programs). This option is particularly useful for programs that +use inlining heavily such as those based on recursive templates with C++. + +Inlining is actually controlled by a number of parameters, which may be +specified individually by using @option{--param @var{name}=@var{value}}. +The @option{-finline-limit=@var{n}} option sets some of these parameters +as follows: + +@table @gcctabopt +@item max-inline-insns-single + is set to @var{n}/2. +@item max-inline-insns-auto + is set to @var{n}/2. +@item min-inline-insns + is set to 130 or @var{n}/4, whichever is smaller. +@item max-inline-insns-rtl + is set to @var{n}. +@end table + +See below for a documentation of the individual +parameters controlling inlining. + +@emph{Note:} pseudo instruction represents, in this particular context, an +abstract measurement of function's size. In no way does it represent a count +of assembly instructions and as such its exact meaning might change from one +release to an another. + +@item -fkeep-inline-functions +@opindex fkeep-inline-functions +In C, emit @code{static} functions that are declared @code{inline} +into the object file, even if the function has been inlined into all +of its callers. This switch does not affect functions using the +@code{extern inline} extension in GNU C@. In C++, emit any and all +inline functions into the object file. + +@item -fkeep-static-consts +@opindex fkeep-static-consts +Emit variables declared @code{static const} when optimization isn't turned +on, even if the variables aren't referenced. + +GCC enables this option by default. If you want to force the compiler to +check if the variable was referenced, regardless of whether or not +optimization is turned on, use the @option{-fno-keep-static-consts} option. + +@c APPLE LOCAL begin ARM conditionally disable local RA +@item -flocal-alloc +(APPLE ONLY) Enable the local (intra-basic-block) register allocator. + +GCC enables this option by default. If you want to force the compiler to +supress register allocation within a basic block, use the +@option{-fno-local-alloc} option. This option cannot be disabled with +@option{-O0}, for correctness reasons. +@c APPLE LOCAL end ARM conditionally disable local RA + +@item -fmerge-constants +Attempt to merge identical constants (string constants and floating point +constants) across compilation units. + +This option is the default for optimized compilation if the assembler and +linker support it. Use @option{-fno-merge-constants} to inhibit this +behavior. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fmerge-all-constants +Attempt to merge identical constants and identical variables. + +This option implies @option{-fmerge-constants}. In addition to +@option{-fmerge-constants} this considers e.g.@: even constant initialized +arrays or initialized constant variables with integral or floating point +types. Languages like C or C++ require each non-automatic variable to +have distinct location, so using this option will result in non-conforming +behavior. + +@item -fmodulo-sched +@opindex fmodulo-sched +Perform swing modulo scheduling immediately before the first scheduling +pass. This pass looks at innermost loops and reorders their +instructions by overlapping different iterations. + +@item -fno-branch-count-reg +@opindex fno-branch-count-reg +Do not use ``decrement and branch'' instructions on a count register, +but instead generate a sequence of instructions that decrement a +register, compare it against zero, then branch based upon the result. +This option is only meaningful on architectures that support such +instructions, which include x86, PowerPC, IA-64 and S/390. + +The default is @option{-fbranch-count-reg}. + +@item -fno-function-cse +@opindex fno-function-cse +Do not put function addresses in registers; make each instruction that +calls a constant function contain the function's address explicitly. + +This option results in less efficient code, but some strange hacks +that alter the assembler output may be confused by the optimizations +performed when this option is not used. + +The default is @option{-ffunction-cse} + +@item -fno-zero-initialized-in-bss +@opindex fno-zero-initialized-in-bss +If the target supports a BSS section, GCC by default puts variables that +are initialized to zero into BSS@. This can save space in the resulting +code. + +This option turns off this behavior because some programs explicitly +rely on variables going to the data section. E.g., so that the +resulting executable can find the beginning of that section and/or make +assumptions based on that. + +The default is @option{-fzero-initialized-in-bss}. + +@item -fbounds-check +@opindex fbounds-check +For front-ends that support it, generate additional code to check that +indices used to access arrays are within the declared range. This is +currently only supported by the Java and Fortran front-ends, where +this option defaults to true and false respectively. + +@item -fmudflap -fmudflapth -fmudflapir +@opindex fmudflap +@opindex fmudflapth +@opindex fmudflapir +@cindex bounds checking +@cindex mudflap +For front-ends that support it (C and C++), instrument all risky +pointer/array dereferencing operations, some standard library +string/heap functions, and some other associated constructs with +range/validity tests. Modules so instrumented should be immune to +buffer overflows, invalid heap use, and some other classes of C/C++ +programming errors. The instrumentation relies on a separate runtime +library (@file{libmudflap}), which will be linked into a program if +@option{-fmudflap} is given at link time. Run-time behavior of the +instrumented program is controlled by the @env{MUDFLAP_OPTIONS} +environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out} +for its options. + +Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to +link if your program is multi-threaded. Use @option{-fmudflapir}, in +addition to @option{-fmudflap} or @option{-fmudflapth}, if +instrumentation should ignore pointer reads. This produces less +instrumentation (and therefore faster execution) and still provides +some protection against outright memory corrupting writes, but allows +erroneously read data to propagate within a program. + +@item -fthread-jumps +@opindex fthread-jumps +Perform optimizations where we check to see if a jump branches to a +location where another comparison subsumed by the first is found. If +so, the first branch is redirected to either the destination of the +second branch or a point immediately following it, depending on whether +the condition is known to be true or false. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fcse-follow-jumps +@opindex fcse-follow-jumps +In common subexpression elimination, scan through jump instructions +when the target of the jump is not reached by any other path. For +example, when CSE encounters an @code{if} statement with an +@code{else} clause, CSE will follow the jump when the condition +tested is false. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fcse-skip-blocks +@opindex fcse-skip-blocks +This is similar to @option{-fcse-follow-jumps}, but causes CSE to +follow jumps which conditionally skip over blocks. When CSE +encounters a simple @code{if} statement with no else clause, +@option{-fcse-skip-blocks} causes CSE to follow the jump around the +body of the @code{if}. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -frerun-cse-after-loop +@opindex frerun-cse-after-loop +Re-run common subexpression elimination after loop optimizations has been +performed. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fgcse +@opindex fgcse +Perform a global common subexpression elimination pass. +This pass also performs global constant and copy propagation. + +@emph{Note:} When compiling a program using computed gotos, a GCC +extension, you may get better runtime performance if you disable +the global common subexpression elimination pass by adding +@option{-fno-gcse} to the command line. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fgcse-lm +@opindex fgcse-lm +When @option{-fgcse-lm} is enabled, global common subexpression elimination will +attempt to move loads which are only killed by stores into themselves. This +allows a loop containing a load/store sequence to be changed to a load outside +the loop, and a copy/store within the loop. + +Enabled by default when gcse is enabled. + +@item -fgcse-sm +@opindex fgcse-sm +When @option{-fgcse-sm} is enabled, a store motion pass is run after +global common subexpression elimination. This pass will attempt to move +stores out of loops. When used in conjunction with @option{-fgcse-lm}, +loops containing a load/store sequence can be changed to a load before +the loop and a store after the loop. + +Not enabled at any optimization level. + +@item -fgcse-las +@opindex fgcse-las +When @option{-fgcse-las} is enabled, the global common subexpression +elimination pass eliminates redundant loads that come after stores to the +same memory location (both partial and full redundancies). + +Not enabled at any optimization level. + +@item -fgcse-after-reload +@opindex fgcse-after-reload +When @option{-fgcse-after-reload} is enabled, a redundant load elimination +pass is performed after reload. The purpose of this pass is to cleanup +redundant spilling. + +@item -funsafe-loop-optimizations +@opindex funsafe-loop-optimizations +If given, the loop optimizer will assume that loop indices do not +overflow, and that the loops with nontrivial exit condition are not +infinite. This enables a wider range of loop optimizations even if +the loop optimizer itself cannot prove that these assumptions are valid. +Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you +if it finds this kind of loop. + +@item -fcrossjumping +@opindex crossjumping +Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The +resulting code may or may not perform better than without cross-jumping. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fif-conversion +@opindex if-conversion +Attempt to transform conditional jumps into branch-less equivalents. This +include use of conditional moves, min, max, set flags and abs instructions, and +some tricks doable by standard arithmetics. The use of conditional execution +on chips where it is available is controlled by @code{if-conversion2}. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fif-conversion2 +@opindex if-conversion2 +Use conditional execution (where available) to transform conditional jumps into +branch-less equivalents. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fdelete-null-pointer-checks +@opindex fdelete-null-pointer-checks +Use global dataflow analysis to identify and eliminate useless checks +for null pointers. The compiler assumes that dereferencing a null +pointer would have halted the program. If a pointer is checked after +it has already been dereferenced, it cannot be null. + +In some environments, this assumption is not true, and programs can +safely dereference null pointers. Use +@option{-fno-delete-null-pointer-checks} to disable this optimization +for programs which depend on that behavior. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fexpensive-optimizations +@opindex fexpensive-optimizations +Perform a number of minor optimizations that are relatively expensive. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -foptimize-register-move +@itemx -fregmove +@opindex foptimize-register-move +@opindex fregmove +Attempt to reassign register numbers in move instructions and as +operands of other simple instructions in order to maximize the amount of +register tying. This is especially helpful on machines with two-operand +instructions. + +Note @option{-fregmove} and @option{-foptimize-register-move} are the same +optimization. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fdelayed-branch +@opindex fdelayed-branch +If supported for the target machine, attempt to reorder instructions +to exploit instruction slots available after delayed branch +instructions. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fschedule-insns +@opindex fschedule-insns +If supported for the target machine, attempt to reorder instructions to +eliminate execution stalls due to required data being unavailable. This +helps machines that have slow floating point or memory load instructions +by allowing other instructions to be issued until the result of the load +or floating point instruction is required. + +@c APPLE LOCAL begin 4231761 5591571 +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} for PPC targets; +ignored for x86 targets (APPLE ONLY). +@c APPLE LOCAL end 4231761 5591571 + +@item -fschedule-insns2 +@opindex fschedule-insns2 +Similar to @option{-fschedule-insns}, but requests an additional pass of +instruction scheduling after register allocation has been done. This is +especially useful on machines with a relatively small number of +registers and where memory load instructions take more than one cycle. + +@c APPLE LOCAL begin 4231761 5591571 +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} for PPC targets; +ignored for x86 targets (APPLE ONLY). +@c APPLE LOCAL end 4231761 5591571 + +@item -fno-sched-interblock +@opindex fno-sched-interblock +Don't schedule instructions across basic blocks. This is normally +enabled by default when scheduling before register allocation, i.e.@: +with @option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fno-sched-spec +@opindex fno-sched-spec +Don't allow speculative motion of non-load instructions. This is normally +enabled by default when scheduling before register allocation, i.e.@: +with @option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-spec-load +@opindex fsched-spec-load +Allow speculative motion of some load instructions. This only makes +sense when scheduling before register allocation, i.e.@: with +@option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-spec-load-dangerous +@opindex fsched-spec-load-dangerous +Allow speculative motion of more load instructions. This only makes +sense when scheduling before register allocation, i.e.@: with +@option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-stalled-insns=@var{n} +@opindex fsched-stalled-insns +Define how many insns (if any) can be moved prematurely from the queue +of stalled insns into the ready list, during the second scheduling pass. + +@item -fsched-stalled-insns-dep=@var{n} +@opindex fsched-stalled-insns-dep +Define how many insn groups (cycles) will be examined for a dependency +on a stalled insn that is candidate for premature removal from the queue +of stalled insns. Has an effect only during the second scheduling pass, +and only if @option{-fsched-stalled-insns} is used and its value is not zero. + +@item -fsched2-use-superblocks +@opindex fsched2-use-superblocks +When scheduling after register allocation, do use superblock scheduling +algorithm. Superblock scheduling allows motion across basic block boundaries +resulting on faster schedules. This option is experimental, as not all machine +descriptions used by GCC model the CPU closely enough to avoid unreliable +results from the algorithm. + +This only makes sense when scheduling after register allocation, i.e.@: with +@option{-fschedule-insns2} or at @option{-O2} or higher. + +@item -fsched2-use-traces +@opindex fsched2-use-traces +Use @option{-fsched2-use-superblocks} algorithm when scheduling after register +allocation and additionally perform code duplication in order to increase the +size of superblocks using tracer pass. See @option{-ftracer} for details on +trace formation. + +This mode should produce faster but significantly longer programs. Also +without @option{-fbranch-probabilities} the traces constructed may not +match the reality and hurt the performance. This only makes +sense when scheduling after register allocation, i.e.@: with +@option{-fschedule-insns2} or at @option{-O2} or higher. + +@item -fsee +@opindex fsee +Eliminates redundant extension instructions and move the non redundant +ones to optimal placement using LCM. + +@item -freschedule-modulo-scheduled-loops +@opindex fscheduling-in-modulo-scheduled-loops +The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled +we may want to prevent the later scheduling passes from changing its schedule, we use this +option to control that. + +@item -fcaller-saves +@opindex fcaller-saves +Enable values to be allocated in registers that will be clobbered by +function calls, by emitting extra instructions to save and restore the +registers around such calls. Such allocation is done only when it +seems to result in better code than would otherwise be produced. + +This option is always enabled by default on certain machines, usually +those which have no call-preserved registers to use instead. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -ftree-pre +Perform Partial Redundancy Elimination (PRE) on trees. This flag is +enabled by default at @option{-O2} and @option{-O3}. + +@item -ftree-fre +Perform Full Redundancy Elimination (FRE) on trees. The difference +between FRE and PRE is that FRE only considers expressions +that are computed on all paths leading to the redundant computation. +This analysis faster than PRE, though it exposes fewer redundancies. +This flag is enabled by default at @option{-O} and higher. + +@item -ftree-copy-prop +Perform copy propagation on trees. This pass eliminates unnecessary +copy operations. This flag is enabled by default at @option{-O} and +higher. + +@item -ftree-store-copy-prop +Perform copy propagation of memory loads and stores. This pass +eliminates unnecessary copy operations in memory references +(structures, global variables, arrays, etc). This flag is enabled by +default at @option{-O2} and higher. + +@item -ftree-salias +Perform structural alias analysis on trees. This flag +is enabled by default at @option{-O} and higher. + +@item -fipa-pta +Perform interprocedural pointer analysis. + +@item -ftree-sink +Perform forward store motion on trees. This flag is +enabled by default at @option{-O} and higher. + +@item -ftree-ccp +Perform sparse conditional constant propagation (CCP) on trees. This +pass only operates on local scalar variables and is enabled by default +at @option{-O} and higher. + +@item -ftree-store-ccp +Perform sparse conditional constant propagation (CCP) on trees. This +pass operates on both local scalar variables and memory stores and +loads (global variables, structures, arrays, etc). This flag is +enabled by default at @option{-O2} and higher. + +@item -ftree-dce +Perform dead code elimination (DCE) on trees. This flag is enabled by +default at @option{-O} and higher. + +@item -ftree-dominator-opts +Perform a variety of simple scalar cleanups (constant/copy +propagation, redundancy elimination, range propagation and expression +simplification) based on a dominator tree traversal. This also +performs jump threading (to reduce jumps to jumps). This flag is +enabled by default at @option{-O} and higher. + +@item -ftree-ch +Perform loop header copying on trees. This is beneficial since it increases +effectiveness of code motion optimizations. It also saves one jump. This flag +is enabled by default at @option{-O} and higher. It is not enabled +@c APPLE LOCAL 4231761 -Oz +for @option{-Os} or @option{-Oz} (APPLE ONLY), since it usually increases code size. + +@item -ftree-loop-optimize +Perform loop optimizations on trees. This flag is enabled by default +at @option{-O} and higher. + +@item -ftree-loop-linear +Perform linear loop transformations on tree. This flag can improve cache +performance and allow further loop optimizations to take place. +@c APPLE LOCAL begin buggy opt 4420531 3950497 3984937 4013797 +This flag is known to have bugs that cause incorrect code to be generated in +some rare cases. Note this flag is included in -fast. +@c APPLE LOCAL end buggy opt 4420531 3950497 3984937 4013797 + +@item -ftree-loop-im +Perform loop invariant motion on trees. This pass moves only invariants that +would be hard to handle at RTL level (function calls, operations that expand to +nontrivial sequences of insns). With @option{-funswitch-loops} it also moves +operands of conditions that are invariant out of the loop, so that we can use +just trivial invariantness analysis in loop unswitching. The pass also includes +store motion. + +@item -ftree-loop-ivcanon +Create a canonical counter for number of iterations in the loop for that +determining number of iterations requires complicated analysis. Later +optimizations then may determine the number easily. Useful especially +in connection with unrolling. + +@item -fivopts +Perform induction variable optimizations (strength reduction, induction +variable merging and induction variable elimination) on trees. + +@item -ftree-sra +Perform scalar replacement of aggregates. This pass replaces structure +references with scalars to prevent committing structures to memory too +early. This flag is enabled by default at @option{-O} and higher. + +@item -ftree-copyrename +Perform copy renaming on trees. This pass attempts to rename compiler +temporaries to other variables at copy locations, usually resulting in +variable names which more closely resemble the original variables. This flag +is enabled by default at @option{-O} and higher. + +@item -ftree-ter +Perform temporary expression replacement during the SSA->normal phase. Single +use/single def temporaries are replaced at their use location with their +defining expression. This results in non-GIMPLE code, but gives the expanders +much more complex trees to work on resulting in better RTL generation. This is +enabled by default at @option{-O} and higher. + +@item -ftree-lrs +Perform live range splitting during the SSA->normal phase. Distinct live +ranges of a variable are split into unique variables, allowing for better +optimization later. This is enabled by default at @option{-O} and higher. + +@item -ftree-vectorize +Perform loop vectorization on trees. + +@c APPLE LOCAL begin optimization +In Apple's version of GCC, @option{-fstrict-aliasing} is enabled by default +when loop vectorization is enabled. See @option{-fstrict-aliasing} document +for more information. +@c APPLE LOCAL end optimization + +@item -ftree-vect-loop-version +@opindex ftree-vect-loop-version +Perform loop versioning when doing loop vectorization on trees. When a loop +appears to be vectorizable except that data alignment or data dependence cannot +be determined at compile time then vectorized and non-vectorized versions of +the loop are generated along with runtime checks for alignment or dependence +to control which version is executed. This option is enabled by default +except at level @option{-Os} where it is disabled. + +@item -ftree-vrp +Perform Value Range Propagation on trees. This is similar to the +constant propagation pass, but instead of values, ranges of values are +propagated. This allows the optimizers to remove unnecessary range +checks like array bound checks and null pointer checks. This is +enabled by default at @option{-O2} and higher. Null pointer check +elimination is only done if @option{-fdelete-null-pointer-checks} is +enabled. + +@item -ftracer +@opindex ftracer +Perform tail duplication to enlarge superblock size. This transformation +simplifies the control flow of the function allowing other optimizations to do +better job. + +@item -funroll-loops +@opindex funroll-loops +Unroll loops whose number of iterations can be determined at compile +time or upon entry to the loop. @option{-funroll-loops} implies +@option{-frerun-cse-after-loop}. This option makes code larger, +and may or may not make it run faster. + +@item -funroll-all-loops +@opindex funroll-all-loops +Unroll all loops, even if their number of iterations is uncertain when +the loop is entered. This usually makes programs run more slowly. +@option{-funroll-all-loops} implies the same options as +@option{-funroll-loops}, + +@item -fsplit-ivs-in-unroller +@opindex fsplit-ivs-in-unroller +Enables expressing of values of induction variables in later iterations +of the unrolled loop using the value in the first iteration. This breaks +long dependency chains, thus improving efficiency of the scheduling passes. + +Combination of @option{-fweb} and CSE is often sufficient to obtain the +same effect. However in cases the loop body is more complicated than +a single basic block, this is not reliable. It also does not work at all +on some of the architectures due to restrictions in the CSE pass. + +This optimization is enabled by default. + +@item -fvariable-expansion-in-unroller +@opindex fvariable-expansion-in-unroller +With this option, the compiler will create multiple copies of some +local variables when unrolling a loop which can result in superior code. + +@item -fprefetch-loop-arrays +@opindex fprefetch-loop-arrays +If supported by the target machine, generate instructions to prefetch +memory to improve the performance of loops that access large arrays. + +This option may generate better or worse code; results are highly +dependent on the structure of loops within the source code. + +@c APPLE LOCAL 4231761 -Oz +Disabled at levels @option{-Os} and @option{-Oz} (APPLE ONLY). + +@item -fno-peephole +@itemx -fno-peephole2 +@opindex fno-peephole +@opindex fno-peephole2 +Disable any machine-specific peephole optimizations. The difference +between @option{-fno-peephole} and @option{-fno-peephole2} is in how they +are implemented in the compiler; some targets use one, some use the +other, a few use both. + +@option{-fpeephole} is enabled by default. +@c APPLE LOCAL 4231761 -Oz +@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fno-guess-branch-probability +@opindex fno-guess-branch-probability +Do not guess branch probabilities using heuristics. + +GCC will use heuristics to guess branch probabilities if they are +not provided by profiling feedback (@option{-fprofile-arcs}). These +heuristics are based on the control flow graph. If some branch probabilities +are specified by @samp{__builtin_expect}, then the heuristics will be +used to guess branch probabilities for the rest of the control flow graph, +taking the @samp{__builtin_expect} info into account. The interactions +between the heuristics and @samp{__builtin_expect} can be complex, and in +some cases, it may be useful to disable the heuristics so that the effects +of @samp{__builtin_expect} are easier to understand. + +The default is @option{-fguess-branch-probability} at levels +@c APPLE LOCAL 4231761 -Oz +@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -freorder-blocks +@opindex freorder-blocks +Reorder basic blocks in the compiled function in order to reduce number of +taken branches and improve code locality. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -freorder-blocks-and-partition +@opindex freorder-blocks-and-partition +In addition to reordering basic blocks in the compiled function, in order +to reduce number of taken branches, partitions hot and cold basic blocks +into separate sections of the assembly and .o files, to improve +paging and cache locality performance. + +This optimization is automatically turned off in the presence of +exception handling, for linkonce sections, for functions with a user-defined +section attribute and on any architecture that does not support named +sections. + +@item -freorder-functions +@opindex freorder-functions +Reorder functions in the object file in order to +improve code locality. This is implemented by using special +subsections @code{.text.hot} for most frequently executed functions and +@code{.text.unlikely} for unlikely executed functions. Reordering is done by +the linker so object file format must support named sections and linker must +place them in a reasonable way. + +Also profile feedback must be available in to make this option effective. See +@option{-fprofile-arcs} for details. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fstrict-aliasing +@opindex fstrict-aliasing +Allows the compiler to assume the strictest aliasing rules applicable to +the language being compiled. For C (and C++), this activates +optimizations based on the type of expressions. In particular, an +object of one type is assumed never to reside at the same address as an +object of a different type, unless the types are almost the same. For +example, an @code{unsigned int} can alias an @code{int}, but not a +@code{void*} or a @code{double}. A character type may alias any other +type. + +Pay special attention to code like this: +@smallexample +union a_union @{ + int i; + double d; +@}; + +int f() @{ + a_union t; + t.d = 3.0; + return t.i; +@} +@end smallexample +The practice of reading from a different union member than the one most +recently written to (called ``type-punning'') is common. Even with +@option{-fstrict-aliasing}, type-punning is allowed, provided the memory +is accessed through the union type. So, the code above will work as +expected. However, this code might not: +@smallexample +int f() @{ + a_union t; + int* ip; + t.d = 3.0; + ip = &t.i; + return *ip; +@} +@end smallexample + +Every language that wishes to perform language-specific alias analysis +should define a function that computes, given an @code{tree} +node, an alias set for the node. Nodes in different alias sets are not +allowed to alias. For an example, see the C front-end function +@code{c_get_alias_set}. + +@c APPLE LOCAL 4231761 -Oz +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, @option{-Oz} (APPLE ONLY). + +@item -fstrict-overflow +@opindex fstrict-overflow +Allow the compiler to assume strict signed overflow rules, depending +on the language being compiled. For C (and C++) this means that +overflow when doing arithmetic with signed numbers is undefined, which +means that the compiler may assume that it will not happen. This +permits various optimizations. For example, the compiler will assume +that an expression like @code{i + 10 > i} will always be true for +signed @code{i}. This assumption is only valid if signed overflow is +undefined, as the expression is false if @code{i + 10} overflows when +using twos complement arithmetic. When this option is in effect any +attempt to determine whether an operation on signed numbers will +overflow must be written carefully to not actually involve overflow. + +See also the @option{-fwrapv} option. Using @option{-fwrapv} means +that signed overflow is fully defined: it wraps. When +@option{-fwrapv} is used, there is no difference between +@option{-fstrict-overflow} and @option{-fno-strict-overflow}. With +@option{-fwrapv} certain types of overflow are permitted. For +example, if the compiler gets an overflow when doing arithmetic on +constants, the overflowed value can still be used with +@option{-fwrapv}, but not otherwise. + +The @option{-fstrict-overflow} option is enabled at levels +@option{-O2}, @option{-O3}, @option{-Os}. + +@item -falign-functions +@itemx -falign-functions=@var{n} +@opindex falign-functions +Align the start of functions to the next power-of-two greater than +@var{n}, skipping up to @var{n} bytes. For instance, +@option{-falign-functions=32} aligns functions to the next 32-byte +boundary, but @option{-falign-functions=24} would align to the next +32-byte boundary only if this can be done by skipping 23 bytes or less. + +@option{-fno-align-functions} and @option{-falign-functions=1} are +equivalent and mean that functions will not be aligned. + +Some assemblers only support this flag when @var{n} is a power of two; +in that case, it is rounded up. + +If @var{n} is not specified or is zero, use a machine-dependent default. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -falign-labels +@itemx -falign-labels=@var{n} +@opindex falign-labels +Align all branch targets to a power-of-two boundary, skipping up to +@var{n} bytes like @option{-falign-functions}. This option can easily +make code slower, because it must insert dummy operations for when the +branch target is reached in the usual flow of the code. + +@option{-fno-align-labels} and @option{-falign-labels=1} are +equivalent and mean that labels will not be aligned. + +If @option{-falign-loops} or @option{-falign-jumps} are applicable and +are greater than this value, then their values are used instead. + +If @var{n} is not specified or is zero, use a machine-dependent default +which is very likely to be @samp{1}, meaning no alignment. + +Enabled at levels @option{-O2}, @option{-O3}. + +@c APPLE LOCAL begin -falign-loops-max-skip +@item -falign-loops-max-skip +@item -falign-loops-max-skip=@var{n} +@opindex falign-loops-max-skip +Align loops to a power-of-two boundary, but do not skip more than +@var{n} bytes to do so. +@c APPLE LOCAL end -falign-loops-max-skip + +@item -falign-loops +@itemx -falign-loops=@var{n} +@opindex falign-loops +Align loops to a power-of-two boundary, skipping up to @var{n} bytes +like @option{-falign-functions}. The hope is that the loop will be +executed many times, which will make up for any execution of the dummy +operations. + +@option{-fno-align-loops} and @option{-falign-loops=1} are +equivalent and mean that loops will not be aligned. + +If @var{n} is not specified or is zero, use a machine-dependent default. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -falign-jumps +@itemx -falign-jumps=@var{n} +@opindex falign-jumps +Align branch targets to a power-of-two boundary, for branch targets +where the targets can only be reached by jumping, skipping up to @var{n} +bytes like @option{-falign-functions}. In this case, no dummy operations +need be executed. + +@c APPLE LOCAL begin -falign-jumps-max-skip +@item -falign-jumps-max-skip +@itemx -falign-jumps-max-skip=@var{n} +@opindex falign-jump-max-skips +Align branch targets to a power-of-two boundary, but do not skip more than +@var{n} bytes to do so. +@c APPLE LOCAL end -falign-jumps-max-skip + +@option{-fno-align-jumps} and @option{-falign-jumps=1} are +equivalent and mean that loops will not be aligned. + +If @var{n} is not specified or is zero, use a machine-dependent default. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -funit-at-a-time +@opindex funit-at-a-time +Parse the whole compilation unit before starting to produce code. +This allows some extra optimizations to take place but consumes +more memory (in general). There are some compatibility issues +with @emph{unit-at-a-time} mode: +@itemize @bullet +@item +enabling @emph{unit-at-a-time} mode may change the order +in which functions, variables, and top-level @code{asm} statements +are emitted, and will likely break code relying on some particular +ordering. The majority of such top-level @code{asm} statements, +though, can be replaced by @code{section} attributes. The +@option{fno-toplevel-reorder} option may be used to keep the ordering +used in the input file, at the cost of some optimizations. + +@item +@emph{unit-at-a-time} mode removes unreferenced static variables +and functions. This may result in undefined references +when an @code{asm} statement refers directly to variables or functions +that are otherwise unused. In that case either the variable/function +shall be listed as an operand of the @code{asm} statement operand or, +in the case of top-level @code{asm} statements the attribute @code{used} +shall be used on the declaration. + +@item +Static functions now can use non-standard passing conventions that +may break @code{asm} statements calling functions directly. Again, +attribute @code{used} will prevent this behavior. +@end itemize + +As a temporary workaround, @option{-fno-unit-at-a-time} can be used, +but this scheme may not be supported by future releases of GCC@. + +Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fno-toplevel-reorder +Do not reorder top-level functions, variables, and @code{asm} +statements. Output them in the same order that they appear in the +input file. When this option is used, unreferenced static variables +will not be removed. This option is intended to support existing code +which relies on a particular ordering. For new code, it is better to +use attributes. + +@item -fweb +@opindex fweb +Constructs webs as commonly used for register allocation purposes and assign +each web individual pseudo register. This allows the register allocation pass +to operate on pseudos directly, but also strengthens several other optimization +passes, such as CSE, loop optimizer and trivial dead code remover. It can, +however, make debugging impossible, since variables will no longer stay in a +``home register''. + +Enabled by default with @option{-funroll-loops}. + +@item -fwhole-program +@opindex fwhole-program +Assume that the current compilation unit represents whole program being +compiled. All public functions and variables with the exception of @code{main} +and those merged by attribute @code{externally_visible} become static functions +and in a affect gets more aggressively optimized by interprocedural optimizers. +While this option is equivalent to proper use of @code{static} keyword for +programs consisting of single file, in combination with option +@option{--combine} this flag can be used to compile most of smaller scale C +programs since the functions and variables become local for the whole combined +compilation unit, not for the single source file itself. + + +@item -fno-cprop-registers +@opindex fno-cprop-registers +After register allocation and post-register allocation instruction splitting, +we perform a copy-propagation pass to try to reduce scheduling dependencies +and occasionally eliminate the copy. + +@c APPLE LOCAL begin 4231761 -Oz +Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}, +@option{-Oz} (APPLE ONLY). +@c APPLE LOCAL end 4231761 -Oz + +@item -fprofile-generate +@opindex fprofile-generate + +Enable options usually used for instrumenting application to produce +profile useful for later recompilation with profile feedback based +optimization. You must use @option{-fprofile-generate} both when +compiling and when linking your program. + +The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}. + +@item -fprofile-use +@opindex fprofile-use +Enable profile feedback directed optimizations, and optimizations +generally profitable only with profile feedback available. + +The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, +@code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer} + +@end table + +The following options control compiler behavior regarding floating +point arithmetic. These options trade off between speed and +correctness. All must be specifically enabled. + +@table @gcctabopt +@item -ffloat-store +@opindex ffloat-store +Do not store floating point variables in registers, and inhibit other +options that might change whether a floating point value is taken from a +register or memory. + +@cindex floating point precision +This option prevents undesirable excess precision on machines such as +the 68000 where the floating registers (of the 68881) keep more +precision than a @code{double} is supposed to have. Similarly for the +x86 architecture. For most programs, the excess precision does only +good, but a few programs rely on the precise definition of IEEE floating +point. Use @option{-ffloat-store} for such programs, after modifying +them to store all pertinent intermediate computations into variables. + +@item -ffast-math +@opindex ffast-math +Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @* +@option{-fno-trapping-math}, @option{-ffinite-math-only}, +@option{-fno-rounding-math}, @option{-fno-signaling-nans} +and @option{fcx-limited-range}. + +This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +@item -fno-math-errno +@opindex fno-math-errno +Do not set ERRNO after calling math functions that are executed +with a single instruction, e.g., sqrt. A program that relies on +IEEE exceptions for math error handling may want to use this flag +for speed while maintaining IEEE arithmetic compatibility. + +@c APPLE LOCAL begin disable math-errno +@ignore +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-fmath-errno}. +@end ignore +(APPLE ONLY) The Darwin math libraries never set errno, so there is +no point in having the compiler generate code that assumes they +might. Therefore, the default is @option{-fno-math-errno} on Darwin. +@c APPLE LOCAL end disable math-errno + +On Darwin systems, the math library never sets @code{errno}. There is therefore +no reason for the compiler to consider the possibility that it might, +and @option{-fno-math-errno} is the default. + +@item -funsafe-math-optimizations +@opindex funsafe-math-optimizations +Allow optimizations for floating-point arithmetic that (a) assume +that arguments and results are valid and (b) may violate IEEE or +ANSI standards. When used at link-time, it may include libraries +or startup files that change the default FPU control word or other +similar optimizations. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-fno-unsafe-math-optimizations}. + +@item -ffinite-math-only +@opindex ffinite-math-only +Allow optimizations for floating-point arithmetic that assume +that arguments and results are not NaNs or +-Infs. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications. + +The default is @option{-fno-finite-math-only}. + +@item -fno-trapping-math +@opindex fno-trapping-math +Compile code assuming that floating-point operations cannot generate +user-visible traps. These traps include division by zero, overflow, +underflow, inexact result and invalid operation. This option implies +@option{-fno-signaling-nans}. Setting this option may allow faster +code if one relies on ``non-stop'' IEEE arithmetic, for example. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-ftrapping-math}. + +@item -frounding-math +@opindex frounding-math +Disable transformations and optimizations that assume default floating +point rounding behavior. This is round-to-zero for all floating point +to integer conversions, and round-to-nearest for all other arithmetic +truncations. This option should be specified for programs that change +the FP rounding mode dynamically, or that may be executed with a +non-default rounding mode. This option disables constant folding of +floating point expressions at compile-time (which may be affected by +rounding mode) and arithmetic transformations that are unsafe in the +presence of sign-dependent rounding modes. + +The default is @option{-fno-rounding-math}. + +This option is experimental and does not currently guarantee to +disable all GCC optimizations that are affected by rounding mode. +Future versions of GCC may provide finer control of this setting +using C99's @code{FENV_ACCESS} pragma. This command line option +will be used to specify the default state for @code{FENV_ACCESS}. + +@item -frtl-abstract-sequences +@opindex frtl-abstract-sequences +It is a size optimization method. This option is to find identical +sequences of code, which can be turned into pseudo-procedures and +then replace all occurrences with calls to the newly created +subroutine. It is kind of an opposite of @option{-finline-functions}. +This optimization runs at RTL level. + +@item -fsignaling-nans +@opindex fsignaling-nans +Compile code assuming that IEEE signaling NaNs may generate user-visible +traps during floating-point operations. Setting this option disables +optimizations that may change the number of exceptions visible with +signaling NaNs. This option implies @option{-ftrapping-math}. + +This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to +be defined. + +The default is @option{-fno-signaling-nans}. + +This option is experimental and does not currently guarantee to +disable all GCC optimizations that affect signaling NaN behavior. + +@item -fsingle-precision-constant +@opindex fsingle-precision-constant +Treat floating point constant as single precision constant instead of +implicitly converting it to double precision constant. + +@item -fcx-limited-range +@itemx -fno-cx-limited-range +@opindex fcx-limited-range +@opindex fno-cx-limited-range +When enabled, this option states that a range reduction step is not +needed when performing complex division. The default is +@option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}. + +This option controls the default setting of the ISO C99 +@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to +all languages. + +@end table + +The following options control optimizations that may improve +performance, but are not enabled by any @option{-O} options. This +section includes experimental options that may produce broken code. + +@table @gcctabopt +@item -fbranch-probabilities +@opindex fbranch-probabilities +After running a program compiled with @option{-fprofile-arcs} +(@pxref{Debugging Options,, Options for Debugging Your Program or +@command{gcc}}), you can compile it a second time using +@option{-fbranch-probabilities}, to improve optimizations based on +the number of times each branch was taken. When the program +compiled with @option{-fprofile-arcs} exits it saves arc execution +counts to a file called @file{@var{sourcename}.gcda} for each source +file The information in this data file is very dependent on the +structure of the generated code, so you must use the same source code +and the same optimization options for both compilations. + +With @option{-fbranch-probabilities}, GCC puts a +@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. +These can be used to improve optimization. Currently, they are only +used in one place: in @file{reorg.c}, instead of guessing which path a +branch is mostly to take, the @samp{REG_BR_PROB} values are used to +exactly determine which path is taken more often. + +@item -fprofile-values +@opindex fprofile-values +If combined with @option{-fprofile-arcs}, it adds code so that some +data about values of expressions in the program is gathered. + +With @option{-fbranch-probabilities}, it reads back the data gathered +from profiling values of expressions and adds @samp{REG_VALUE_PROFILE} +notes to instructions for their later usage in optimizations. + +Enabled with @option{-fprofile-generate} and @option{-fprofile-use}. + +@item -fvpt +@opindex fvpt +If combined with @option{-fprofile-arcs}, it instructs the compiler to add +a code to gather information about values of expressions. + +With @option{-fbranch-probabilities}, it reads back the data gathered +and actually performs the optimizations based on them. +Currently the optimizations include specialization of division operation +using the knowledge about the value of the denominator. + +@item -frename-registers +@opindex frename-registers +Attempt to avoid false dependencies in scheduled code by making use +of registers left over after register allocation. This optimization +will most benefit processors with lots of registers. Depending on the +debug information format adopted by the target, however, it can +make debugging impossible, since variables will no longer stay in +a ``home register''. + +Enabled by default with @option{-funroll-loops}. + +@item -ftracer +@opindex ftracer +Perform tail duplication to enlarge superblock size. This transformation +simplifies the control flow of the function allowing other optimizations to do +better job. + +Enabled with @option{-fprofile-use}. + +@item -funroll-loops +@opindex funroll-loops +Unroll loops whose number of iterations can be determined at compile time or +upon entry to the loop. @option{-funroll-loops} implies +@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. +It also turns on complete loop peeling (i.e.@: complete removal of loops with +small constant number of iterations). This option makes code larger, and may +or may not make it run faster. + +Enabled with @option{-fprofile-use}. + +@item -funroll-all-loops +@opindex funroll-all-loops +Unroll all loops, even if their number of iterations is uncertain when +the loop is entered. This usually makes programs run more slowly. +@option{-funroll-all-loops} implies the same options as +@option{-funroll-loops}. + +@item -fpeel-loops +@opindex fpeel-loops +Peels the loops for that there is enough information that they do not +roll much (from profile feedback). It also turns on complete loop peeling +(i.e.@: complete removal of loops with small constant number of iterations). + +Enabled with @option{-fprofile-use}. + +@item -fmove-loop-invariants +@opindex fmove-loop-invariants +Enables the loop invariant motion pass in the RTL loop optimizer. Enabled +at level @option{-O1} + +@item -funswitch-loops +@opindex funswitch-loops +Move branches with loop invariant conditions out of the loop, with duplicates +of the loop on both branches (modified according to result of the condition). + +@item -ffunction-sections +@itemx -fdata-sections +@opindex ffunction-sections +@opindex fdata-sections +Place each function or data item into its own section in the output +file if the target supports arbitrary sections. The name of the +function or the name of the data item determines the section's name +in the output file. + +Use these options on systems where the linker can perform optimizations +to improve locality of reference in the instruction space. Most systems +using the ELF object format and SPARC processors running Solaris 2 have +linkers with such optimizations. AIX may have these optimizations in +the future. + +Only use these options when there are significant benefits from doing +so. When you specify these options, the assembler and linker will +create larger object and executable files and will also be slower. +You will not be able to use @code{gprof} on all systems if you +specify this option and you may have problems with debugging if +you specify both this option and @option{-g}. + +@item -fbranch-target-load-optimize +@opindex fbranch-target-load-optimize +Perform branch target register load optimization before prologue / epilogue +threading. +The use of target registers can typically be exposed only during reload, +thus hoisting loads out of loops and doing inter-block scheduling needs +a separate optimization pass. + +@item -fbranch-target-load-optimize2 +@opindex fbranch-target-load-optimize2 +Perform branch target register load optimization after prologue / epilogue +threading. + +@item -fbtr-bb-exclusive +@opindex fbtr-bb-exclusive +When performing branch target register load optimization, don't reuse +branch target registers in within any basic block. + +@item -fstack-protector +Emit extra code to check for buffer overflows, such as stack smashing +attacks. This is done by adding a guard variable to functions with +vulnerable objects. This includes functions that call alloca, and +functions with buffers larger than 8 bytes. The guards are initialized +when a function is entered and then checked when the function exits. +If a guard check fails, an error message is printed and the program exits. + +@item -fstack-protector-all +Like @option{-fstack-protector} except that all functions are protected. + +@item -fsection-anchors +@opindex fsection-anchors +Try to reduce the number of symbolic address calculations by using +shared ``anchor'' symbols to address nearby objects. This transformation +can help to reduce the number of GOT entries and GOT accesses on some +targets. + +For example, the implementation of the following function @code{foo}: + +@smallexample +static int a, b, c; +int foo (void) @{ return a + b + c; @} +@end smallexample + +would usually calculate the addresses of all three variables, but if you +compile it with @option{-fsection-anchors}, it will access the variables +from a common anchor point instead. The effect is similar to the +following pseudocode (which isn't valid C): + +@smallexample +int foo (void) +@{ + register int *xr = &x; + return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; +@} +@end smallexample + +Not all targets support this option. + +@item --param @var{name}=@var{value} +@opindex param +In some places, GCC uses various constants to control the amount of +optimization that is done. For example, GCC will not inline functions +that contain more that a certain number of instructions. You can +control some of these constants on the command-line using the +@option{--param} option. + +The names of specific parameters, and the meaning of the values, are +tied to the internals of the compiler, and are subject to change +without notice in future releases. + +In each case, the @var{value} is an integer. The allowable choices for +@var{name} are given in the following table: + +@table @gcctabopt +@item salias-max-implicit-fields +The maximum number of fields in a variable without direct +structure accesses for which structure aliasing will consider trying +to track each field. The default is 5 + +@item salias-max-array-elements +The maximum number of elements an array can have and its elements +still be tracked individually by structure aliasing. The default is 4 + +@item sra-max-structure-size +The maximum structure size, in bytes, at which the scalar replacement +of aggregates (SRA) optimization will perform block copies. The +default value, 0, implies that GCC will select the most appropriate +size itself. + +@item sra-field-structure-ratio +The threshold ratio (as a percentage) between instantiated fields and +the complete structure size. We say that if the ratio of the number +of bytes in instantiated fields to the number of bytes in the complete +structure exceeds this parameter, then block copies are not used. The +default is 75. + +@item max-crossjump-edges +The maximum number of incoming edges to consider for crossjumping. +The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in +the number of edges incoming to each block. Increasing values mean +more aggressive optimization, making the compile time increase with +probably small improvement in executable size. + +@item min-crossjump-insns +The minimum number of instructions which must be matched at the end +of two blocks before crossjumping will be performed on them. This +value is ignored in the case where all instructions in the block being +crossjumped from are matched. The default value is 5. + +@item max-grow-copy-bb-insns +The maximum code size expansion factor when copying basic blocks +instead of jumping. The expansion is relative to a jump instruction. +The default value is 8. + +@item max-goto-duplication-insns +The maximum number of instructions to duplicate to a block that jumps +to a computed goto. To avoid @math{O(N^2)} behavior in a number of +passes, GCC factors computed gotos early in the compilation process, +and unfactors them as late as possible. Only computed jumps at the +end of a basic blocks with no more than max-goto-duplication-insns are +unfactored. The default value is 8. + +@item max-delay-slot-insn-search +The maximum number of instructions to consider when looking for an +instruction to fill a delay slot. If more than this arbitrary number of +instructions is searched, the time savings from filling the delay slot +will be minimal so stop searching. Increasing values mean more +aggressive optimization, making the compile time increase with probably +small improvement in executable run time. + +@item max-delay-slot-live-search +When trying to fill delay slots, the maximum number of instructions to +consider when searching for a block with valid live register +information. Increasing this arbitrarily chosen value means more +aggressive optimization, increasing the compile time. This parameter +should be removed when the delay slot code is rewritten to maintain the +control-flow graph. + +@item max-gcse-memory +The approximate maximum amount of memory that will be allocated in +order to perform the global common subexpression elimination +optimization. If more memory than specified is required, the +optimization will not be done. + +@item max-gcse-passes +The maximum number of passes of GCSE to run. The default is 1. + +@item max-pending-list-length +The maximum number of pending dependencies scheduling will allow +before flushing the current state and starting over. Large functions +with few branches or calls can create excessively large lists which +needlessly consume memory and resources. + +@item max-inline-insns-single +Several parameters control the tree inliner used in gcc. +This number sets the maximum number of instructions (counted in GCC's +internal representation) in a single function that the tree inliner +will consider for inlining. This only affects functions declared +inline and methods implemented in a class declaration (C++). +The default value is 450. + +@item max-inline-insns-auto +When you use @option{-finline-functions} (included in @option{-O3}), +a lot of functions that would otherwise not be considered for inlining +by the compiler will be investigated. To those functions, a different +(more restrictive) limit compared to functions declared inline can +be applied. +The default value is 90. + +@item large-function-insns +The limit specifying really large functions. For functions larger than this +limit after inlining inlining is constrained by +@option{--param large-function-growth}. This parameter is useful primarily +to avoid extreme compilation time caused by non-linear algorithms used by the +backend. +This parameter is ignored when @option{-funit-at-a-time} is not used. +The default value is 2700. + +@item large-function-growth +Specifies maximal growth of large function caused by inlining in percents. +This parameter is ignored when @option{-funit-at-a-time} is not used. +The default value is 100 which limits large function growth to 2.0 times +the original size. + +@item large-unit-insns +The limit specifying large translation unit. Growth caused by inlining of +units larger than this limit is limited by @option{--param inline-unit-growth}. +For small units this might be too tight (consider unit consisting of function A +that is inline and B that just calls A three time. If B is small relative to +A, the growth of unit is 300\% and yet such inlining is very sane. For very +large units consisting of small inlininable functions however the overall unit +growth limit is needed to avoid exponential explosion of code size. Thus for +smaller units, the size is increased to @option{--param large-unit-insns} +before applying @option{--param inline-unit-growth}. The default is 10000 + +@item inline-unit-growth +Specifies maximal overall growth of the compilation unit caused by inlining. +This parameter is ignored when @option{-funit-at-a-time} is not used. +The default value is 50 which limits unit growth to 1.5 times the original +size. + +@item max-inline-insns-recursive +@itemx max-inline-insns-recursive-auto +Specifies maximum number of instructions out-of-line copy of self recursive inline +function can grow into by performing recursive inlining. + +For functions declared inline @option{--param max-inline-insns-recursive} is +taken into account. For function not declared inline, recursive inlining +happens only when @option{-finline-functions} (included in @option{-O3}) is +enabled and @option{--param max-inline-insns-recursive-auto} is used. The +default value is 450. + +@item max-inline-recursive-depth +@itemx max-inline-recursive-depth-auto +Specifies maximum recursion depth used by the recursive inlining. + +For functions declared inline @option{--param max-inline-recursive-depth} is +taken into account. For function not declared inline, recursive inlining +happens only when @option{-finline-functions} (included in @option{-O3}) is +enabled and @option{--param max-inline-recursive-depth-auto} is used. The +default value is 450. + +@item min-inline-recursive-probability +Recursive inlining is profitable only for function having deep recursion +in average and can hurt for function having little recursion depth by +increasing the prologue size or complexity of function body to other +optimizers. + +When profile feedback is available (see @option{-fprofile-generate}) the actual +recursion depth can be guessed from probability that function will recurse via +given call expression. This parameter limits inlining only to call expression +whose probability exceeds given threshold (in percents). The default value is +10. + +@item inline-call-cost +Specify cost of call instruction relative to simple arithmetics operations +(having cost of 1). Increasing this cost disqualifies inlining of non-leaf +functions and at the same time increases size of leaf function that is believed to +reduce function size by being inlined. In effect it increases amount of +inlining for code having large abstraction penalty (many functions that just +pass the arguments to other functions) and decrease inlining for code with low +abstraction penalty. The default value is 16. + +@item max-unrolled-insns +The maximum number of instructions that a loop should have if that loop +is unrolled, and if the loop is unrolled, it determines how many times +the loop code is unrolled. + +@item max-average-unrolled-insns +The maximum number of instructions biased by probabilities of their execution +that a loop should have if that loop is unrolled, and if the loop is unrolled, +it determines how many times the loop code is unrolled. + +@item max-unroll-times +The maximum number of unrollings of a single loop. + +@item max-peeled-insns +The maximum number of instructions that a loop should have if that loop +is peeled, and if the loop is peeled, it determines how many times +the loop code is peeled. + +@item max-peel-times +The maximum number of peelings of a single loop. + +@item max-completely-peeled-insns +The maximum number of insns of a completely peeled loop. + +@item max-completely-peel-times +The maximum number of iterations of a loop to be suitable for complete peeling. + +@item max-unswitch-insns +The maximum number of insns of an unswitched loop. + +@item max-unswitch-level +The maximum number of branches unswitched in a single loop. + +@item lim-expensive +The minimum cost of an expensive expression in the loop invariant motion. + +@item iv-consider-all-candidates-bound +Bound on number of candidates for induction variables below that +all candidates are considered for each use in induction variable +optimizations. Only the most relevant candidates are considered +if there are more candidates, to avoid quadratic time complexity. + +@item iv-max-considered-uses +The induction variable optimizations give up on loops that contain more +induction variable uses. + +@item iv-always-prune-cand-set-bound +If number of candidates in the set is smaller than this value, +we always try to remove unnecessary ivs from the set during its +optimization when a new iv is added to the set. + +@item scev-max-expr-size +Bound on size of expressions used in the scalar evolutions analyzer. +Large expressions slow the analyzer. + +@item vect-max-version-checks +The maximum number of runtime checks that can be performed when doing +loop versioning in the vectorizer. See option ftree-vect-loop-version +for more information. + +@item max-iterations-to-track + +The maximum number of iterations of a loop the brute force algorithm +for analysis of # of iterations of the loop tries to evaluate. + +@item hot-bb-count-fraction +Select fraction of the maximal count of repetitions of basic block in program +given basic block needs to have to be considered hot. + +@item hot-bb-frequency-fraction +Select fraction of the maximal frequency of executions of basic block in +function given basic block needs to have to be considered hot + +@item max-predicted-iterations +The maximum number of loop iterations we predict statically. This is useful +in cases where function contain single loop with known bound and other loop +with unknown. We predict the known number of iterations correctly, while +the unknown number of iterations average to roughly 10. This means that the +loop without bounds would appear artificially cold relative to the other one. + +@item tracer-dynamic-coverage +@itemx tracer-dynamic-coverage-feedback + +This value is used to limit superblock formation once the given percentage of +executed instructions is covered. This limits unnecessary code size +expansion. + +The @option{tracer-dynamic-coverage-feedback} is used only when profile +feedback is available. The real profiles (as opposed to statically estimated +ones) are much less balanced allowing the threshold to be larger value. + +@item tracer-max-code-growth +Stop tail duplication once code growth has reached given percentage. This is +rather hokey argument, as most of the duplicates will be eliminated later in +cross jumping, so it may be set to much higher values than is the desired code +growth. + +@item tracer-min-branch-ratio + +Stop reverse growth when the reverse probability of best edge is less than this +threshold (in percent). + +@item tracer-min-branch-ratio +@itemx tracer-min-branch-ratio-feedback + +Stop forward growth if the best edge do have probability lower than this +threshold. + +Similarly to @option{tracer-dynamic-coverage} two values are present, one for +compilation for profile feedback and one for compilation without. The value +for compilation with profile feedback needs to be more conservative (higher) in +order to make tracer effective. + +@item max-cse-path-length + +Maximum number of basic blocks on path that cse considers. The default is 10. + +@item max-cse-insns +The maximum instructions CSE process before flushing. The default is 1000. + +@item global-var-threshold + +Counts the number of function calls (@var{n}) and the number of +call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a +single artificial variable will be created to represent all the +call-clobbered variables at function call sites. This artificial +variable will then be made to alias every call-clobbered variable. +(done as @code{int * size_t} on the host machine; beware overflow). + +@item max-aliased-vops + +Maximum number of virtual operands allowed to represent aliases +before triggering the alias grouping heuristic. Alias grouping +reduces compile times and memory consumption needed for aliasing at +the expense of precision loss in alias information. + +@item ggc-min-expand + +GCC uses a garbage collector to manage its own memory allocation. This +parameter specifies the minimum percentage by which the garbage +collector's heap should be allowed to expand between collections. +Tuning this may improve compilation speed; it has no effect on code +generation. + +The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when +RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is +the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If +GCC is not able to calculate RAM on a particular platform, the lower +bound of 30% is used. Setting this parameter and +@option{ggc-min-heapsize} to zero causes a full collection to occur at +every opportunity. This is extremely slow, but can be useful for +debugging. + +@item ggc-min-heapsize + +Minimum size of the garbage collector's heap before it begins bothering +to collect garbage. The first collection occurs after the heap expands +by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, +tuning this may improve compilation speed, and has no effect on code +generation. + +The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which +tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but +with a lower bound of 4096 (four megabytes) and an upper bound of +131072 (128 megabytes). If GCC is not able to calculate RAM on a +particular platform, the lower bound is used. Setting this parameter +very large effectively disables garbage collection. Setting this +parameter and @option{ggc-min-expand} to zero causes a full collection +to occur at every opportunity. + +@item max-reload-search-insns +The maximum number of instruction reload should look backward for equivalent +register. Increasing values mean more aggressive optimization, making the +compile time increase with probably slightly better performance. The default +value is 100. + +@item max-cselib-memory-locations +The maximum number of memory locations cselib should take into account. +Increasing values mean more aggressive optimization, making the compile time +increase with probably slightly better performance. The default value is 500. + +@item max-flow-memory-locations +Similar as @option{max-cselib-memory-locations} but for dataflow liveness. +The default value is 100. + +@item reorder-blocks-duplicate +@itemx reorder-blocks-duplicate-feedback + +Used by basic block reordering pass to decide whether to use unconditional +branch or duplicate the code on its destination. Code is duplicated when its +estimated size is smaller than this value multiplied by the estimated size of +unconditional jump in the hot spots of the program. + +The @option{reorder-block-duplicate-feedback} is used only when profile +feedback is available and may be set to higher values than +@option{reorder-block-duplicate} since information about the hot spots is more +accurate. + +@item max-sched-ready-insns +The maximum number of instructions ready to be issued the scheduler should +consider at any given time during the first scheduling pass. Increasing +values mean more thorough searches, making the compilation time increase +with probably little benefit. The default value is 100. + +@item max-sched-region-blocks +The maximum number of blocks in a region to be considered for +interblock scheduling. The default value is 10. + +@item max-sched-region-insns +The maximum number of insns in a region to be considered for +interblock scheduling. The default value is 100. + +@item min-spec-prob +The minimum probability (in percents) of reaching a source block +for interblock speculative scheduling. The default value is 40. + +@item max-sched-extend-regions-iters +The maximum number of iterations through CFG to extend regions. +0 - disable region extension, +N - do at most N iterations. +The default value is 0. + +@item max-sched-insn-conflict-delay +The maximum conflict delay for an insn to be considered for speculative motion. +The default value is 3. + +@item sched-spec-prob-cutoff +The minimal probability of speculation success (in percents), so that +speculative insn will be scheduled. +The default value is 40. + +@item max-last-value-rtl + +The maximum size measured as number of RTLs that can be recorded in an expression +in combiner for a pseudo register as last known value of that register. The default +is 10000. + +@item integer-share-limit +Small integer constants can use a shared data structure, reducing the +compiler's memory usage and increasing its speed. This sets the maximum +value of a shared integer constant's. The default value is 256. + +@item min-virtual-mappings +Specifies the minimum number of virtual mappings in the incremental +SSA updater that should be registered to trigger the virtual mappings +heuristic defined by virtual-mappings-ratio. The default value is +100. + +@item virtual-mappings-ratio +If the number of virtual mappings is virtual-mappings-ratio bigger +than the number of virtual symbols to be updated, then the incremental +SSA updater switches to a full update for those symbols. The default +ratio is 3. + +@item ssp-buffer-size +The minimum size of buffers (i.e. arrays) that will receive stack smashing +protection when @option{-fstack-protection} is used. + +@item max-jump-thread-duplication-stmts +Maximum number of statements allowed in a block that needs to be +duplicated when threading jumps. + +@item max-fields-for-field-sensitive +Maximum number of fields in a structure we will treat in +a field sensitive manner during pointer analysis. + +@end table +@end table + +@node Preprocessor Options +@section Options Controlling the Preprocessor +@cindex preprocessor options +@cindex options, preprocessor + +These options control the C preprocessor, which is run on each C source +file before actual compilation. + +If you use the @option{-E} option, nothing is done except preprocessing. +Some of these options make sense only together with @option{-E} because +they cause the preprocessor output to be unsuitable for actual +compilation. + +@table @gcctabopt +@c APPLE LOCAL pod error 6089368 +@item -Wp,@var{option} +@opindex Wp +You can use @option{-Wp,@var{option}} to bypass the compiler driver +and pass @var{option} directly through to the preprocessor. If +@var{option} contains commas, it is split into multiple options at the +commas. However, many options are modified, translated or interpreted +by the compiler driver before being passed to the preprocessor, and +@option{-Wp} forcibly bypasses this phase. The preprocessor's direct +interface is undocumented and subject to change, so whenever possible +you should avoid using @option{-Wp} and let the driver handle the +options instead. + +@item -Xpreprocessor @var{option} +@opindex preprocessor +Pass @var{option} as an option to the preprocessor. You can use this to +supply system-specific preprocessor options which GCC does not know how to +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xpreprocessor} twice, once for the option and once for the argument. +@end table + +@include cppopts.texi + +@node Assembler Options +@section Passing Options to the Assembler + +@c prevent bad page break with this line +You can pass options to the assembler. + +@table @gcctabopt +@item -Wa,@var{option} +@opindex Wa +Pass @var{option} as an option to the assembler. If @var{option} +contains commas, it is split into multiple options at the commas. + +@item -Xassembler @var{option} +@opindex Xassembler +Pass @var{option} as an option to the assembler. You can use this to +supply system-specific assembler options which GCC does not know how to +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xassembler} twice, once for the option and once for the argument. + +@end table + +@node Link Options +@section Options for Linking +@cindex link options +@cindex options, linking + +These options come into play when the compiler links object files into +an executable output file. They are meaningless if the compiler is +not doing a link step. + +@c APPLE LOCAL begin linker flags +In addition to the options listed below, Apple's GCC also accepts and +passes nearly all of the options defined by the linker @samp{ld} and by +the library tool @samp{libtool}. Common options include +@samp{-framework}, @samp{-dynamic}, @samp{-bundle}, +@samp{-flat_namespace}, and so forth. See the ld and libtool man pages +for further details. +@c APPLE LOCAL end linker flags + +@table @gcctabopt +@cindex file names +@item @var{object-file-name} +A file name that does not end in a special recognized suffix is +considered to name an object file or library. (Object files are +distinguished from libraries by the linker according to the file +contents.) If linking is done, these object files are used as input +to the linker. + +@item -c +@itemx -S +@itemx -E +@opindex c +@opindex S +@opindex E +If any of these options is used, then the linker is not run, and +object file names should not be used as arguments. @xref{Overall +Options}. + +@cindex Libraries +@item -l@var{library} +@itemx -l @var{library} +@opindex l +Search the library named @var{library} when linking. (The second +alternative with the library as a separate argument is only for +POSIX compliance and is not recommended.) + +It makes a difference where in the command you write this option; the +linker searches and processes libraries and object files in the order they +are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} +after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers +to functions in @samp{z}, those functions may not be loaded. + +The linker searches a standard list of directories for the library, +which is actually a file named @file{lib@var{library}.a}. The linker +then uses this file as if it had been specified precisely by name. + +The directories searched include several standard system directories +plus any that you specify with @option{-L}. + +Normally the files found this way are library files---archive files +whose members are object files. The linker handles an archive file by +scanning through it for members which define symbols that have so far +been referenced but not defined. But if the file that is found is an +ordinary object file, it is linked in the usual fashion. The only +difference between using an @option{-l} option and specifying a file name +is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} +and searches several directories. + +@item -lobjc +@opindex lobjc +You need this special case of the @option{-l} option in order to +link an Objective-C or Objective-C++ program. + +@item -nostartfiles +@opindex nostartfiles +Do not use the standard system startup files when linking. +The standard system libraries are used normally, unless @option{-nostdlib} +or @option{-nodefaultlibs} is used. + +@item -nodefaultlibs +@opindex nodefaultlibs +Do not use the standard system libraries when linking. +Only the libraries you specify will be passed to the linker. +The standard startup files are used normally, unless @option{-nostartfiles} +is used. The compiler may generate calls to @code{memcmp}, +@code{memset}, @code{memcpy} and @code{memmove}. +These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@item -nostdlib +@opindex nostdlib +Do not use the standard system startup files or libraries when linking. +No startup files and only the libraries you specify will be passed to +the linker. The compiler may generate calls to @code{memcmp}, @code{memset}, +@code{memcpy} and @code{memmove}. +These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@cindex @option{-lgcc}, use with @option{-nostdlib} +@cindex @option{-nostdlib} and unresolved references +@cindex unresolved references and @option{-nostdlib} +@cindex @option{-lgcc}, use with @option{-nodefaultlibs} +@cindex @option{-nodefaultlibs} and unresolved references +@cindex unresolved references and @option{-nodefaultlibs} +One of the standard libraries bypassed by @option{-nostdlib} and +@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines +that GCC uses to overcome shortcomings of particular machines, or special +needs for some languages. +(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler +Collection (GCC) Internals}, +for more discussion of @file{libgcc.a}.) +In most cases, you need @file{libgcc.a} even when you want to avoid +other standard libraries. In other words, when you specify @option{-nostdlib} +or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. +This ensures that you have no unresolved references to internal GCC +library subroutines. (For example, @samp{__main}, used to ensure C++ +constructors will be called; @pxref{Collect2,,@code{collect2}, gccint, +GNU Compiler Collection (GCC) Internals}.) + +@item -pie +@opindex pie +Produce a position independent executable on targets which support it. +For predictable results, you must also specify the same set of options +that were used to generate code (@option{-fpie}, @option{-fPIE}, +or model suboptions) when you specify this option. + +@item -rdynamic +@opindex rdynamic +Pass the flag @option{-export-dynamic} to the ELF linker, on targets +that support it. This instructs the linker to add all symbols, not +only used ones, to the dynamic symbol table. This option is needed +for some uses of @code{dlopen} or to allow obtaining backtraces +from within a program. + +@item -s +@opindex s +Remove all symbol table and relocation information from the executable. + +@item -static +@opindex static +On systems that support dynamic linking, this prevents linking with the shared +libraries. On other systems, this option has no effect. + +@c APPLE LOCAL begin manual +This option will not work on Mac OS X unless all libraries (including +@file{libgcc.a}) have also been compiled with @option{-static}. Since +neither a static version of libSystem.dylib nor crt0.o are provided, this +option is not useful to most people. +@c APPLE LOCAL end manual + +@item -shared +@opindex shared +Produce a shared object which can then be linked with other objects to +form an executable. Not all systems support this option. For predictable +results, you must also specify the same set of options that were used to +generate code (@option{-fpic}, @option{-fPIC}, or model suboptions) +when you specify this option.@footnote{On some systems, @samp{gcc -shared} +needs to build supplementary stub code for constructors to work. On +multi-libbed systems, @samp{gcc -shared} must select the correct support +libraries to link against. Failing to supply the correct flags may lead +to subtle defects. Supplying them in cases where they are not necessary +is innocuous.} + +@c APPLE LOCAL begin manual +This option is not supported on Mac OS X. +@c APPLE LOCAL end manual + +@item -shared-libgcc +@itemx -static-libgcc +@opindex shared-libgcc +@opindex static-libgcc +On systems that provide @file{libgcc} as a shared library, these options +force the use of either the shared or static version respectively. +If no shared version of @file{libgcc} was built when the compiler was +configured, these options have no effect. + +There are several situations in which an application should use the +shared @file{libgcc} instead of the static version. The most common +of these is when the application wishes to throw and catch exceptions +across different shared libraries. In that case, each of the libraries +as well as the application itself should use the shared @file{libgcc}. + +Therefore, the G++ and GCJ drivers automatically add +@option{-shared-libgcc} whenever you build a shared library or a main +executable, because C++ and Java programs typically use exceptions, so +this is the right thing to do. + +If, instead, you use the GCC driver to create shared libraries, you may +find that they will not always be linked with the shared @file{libgcc}. +If GCC finds, at its configuration time, that you have a non-GNU linker +or a GNU linker that does not support option @option{--eh-frame-hdr}, +it will link the shared version of @file{libgcc} into shared libraries +by default. Otherwise, it will take advantage of the linker and optimize +away the linking with the shared version of @file{libgcc}, linking with +the static version of libgcc by default. This allows exceptions to +propagate through such shared libraries, without incurring relocation +costs at library load time. + +However, if a library or main executable is supposed to throw or catch +exceptions, you must link it using the G++ or GCJ driver, as appropriate +for the languages used in the program, or using the option +@option{-shared-libgcc}, such that it is linked with the shared +@file{libgcc}. + +@item -symbolic +@opindex symbolic +Bind references to global symbols when building a shared object. Warn +about any unresolved references (unless overridden by the link editor +option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support +this option. + +@item -Xlinker @var{option} +@opindex Xlinker +Pass @var{option} as an option to the linker. You can use this to +supply system-specific linker options which GCC does not know how to +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xlinker} twice, once for the option and once for the argument. +For example, to pass @option{-assert definitions}, you must write +@samp{-Xlinker -assert -Xlinker definitions}. It does not work to write +@option{-Xlinker "-assert definitions"}, because this passes the entire +string as a single argument, which is not what the linker expects. + +@item -Wl,@var{option} +@opindex Wl +Pass @var{option} as an option to the linker. If @var{option} contains +commas, it is split into multiple options at the commas. + +@item -u @var{symbol} +@opindex u +Pretend the symbol @var{symbol} is undefined, to force linking of +library modules to define it. You can use @option{-u} multiple times with +different symbols to force loading of additional library modules. +@end table + +@node Directory Options +@section Options for Directory Search +@cindex directory options +@cindex options, directory search +@cindex search path + +These options specify directories to search for header files, for +libraries and for parts of the compiler: + +@table @gcctabopt +@item -I@var{dir} +@opindex I +Add the directory @var{dir} to the head of the list of directories to be +searched for header files. This can be used to override a system header +file, substituting your own version, since these directories are +searched before the system header file directories. However, you should +not use this option to add directories that contain vendor-supplied +system header files (use @option{-isystem} for that). If you use more than +one @option{-I} option, the directories are scanned in left-to-right +order; the standard system directories come after. + +If a standard system include directory, or a directory specified with +@option{-isystem}, is also specified with @option{-I}, the @option{-I} +option will be ignored. The directory will still be searched but as a +system directory at its normal position in the system include chain. +This is to ensure that GCC's procedure to fix buggy system headers and +the ordering for the include_next directive are not inadvertently changed. +If you really need to change the search order for system directories, +use the @option{-nostdinc} and/or @option{-isystem} options. + +@c APPLE LOCAL begin ARM iwithsysroot 4917039 +The option @option{-iwithsysroot} (APPLE ONLY), if specified with an +absolute path, will prepend the system root directory (if applicable) to +the path and add it to the beginning of the system search paths. If +specified with a relative path, @option{-iwithsysroot} will behave +identically to @option{-isystem}. +@c APPLE LOCAL end ARM iwithsysroot 4917039 + +@item -iquote@var{dir} +@opindex iquote +Add the directory @var{dir} to the head of the list of directories to +be searched for header files only for the case of @samp{#include +"@var{file}"}; they are not searched for @samp{#include <@var{file}>}, +otherwise just like @option{-I}. + +@item -L@var{dir} +@opindex L +Add directory @var{dir} to the list of directories to be searched +for @option{-l}. + +@item -B@var{prefix} +@opindex B +This option specifies where to find the executables, libraries, +include files, and data files of the compiler itself. + +The compiler driver program runs one or more of the subprograms +@file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries +@var{prefix} as a prefix for each program it tries to run, both with and +without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). + +For each subprogram to be run, the compiler driver first tries the +@option{-B} prefix, if any. If that name is not found, or if @option{-B} +was not specified, the driver tries two standard prefixes, which are +@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of +those results in a file name that is found, the unmodified program +name is searched for using the directories specified in your +@env{PATH} environment variable. + +The compiler will check to see if the path provided by the @option{-B} +refers to a directory, and if necessary it will add a directory +separator character at the end of the path. + +@option{-B} prefixes that effectively specify directory names also apply +to libraries in the linker, because the compiler translates these +options into @option{-L} options for the linker. They also apply to +includes files in the preprocessor, because the compiler translates these +options into @option{-isystem} options for the preprocessor. In this case, +the compiler appends @samp{include} to the prefix. + +The run-time support file @file{libgcc.a} can also be searched for using +the @option{-B} prefix, if needed. If it is not found there, the two +standard prefixes above are tried, and that is all. The file is left +out of the link if it is not found by those means. + +Another way to specify a prefix much like the @option{-B} prefix is to use +the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment +Variables}. + +As a special kludge, if the path provided by @option{-B} is +@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to +9, then it will be replaced by @file{[dir/]include}. This is to help +with boot-strapping the compiler. + +@item -specs=@var{file} +@opindex specs +Process @var{file} after the compiler reads in the standard @file{specs} +file, in order to override the defaults that the @file{gcc} driver +program uses when determining what switches to pass to @file{cc1}, +@file{cc1plus}, @file{as}, @file{ld}, etc. More than one +@option{-specs=@var{file}} can be specified on the command line, and they +are processed in order, from left to right. + +@item --sysroot=@var{dir} +@opindex sysroot +Use @var{dir} as the logical root directory for headers and libraries. +For example, if the compiler would normally search for headers in +@file{/usr/include} and libraries in @file{/usr/lib}, it will instead +search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. + +With Apple's version of GCC, this option is effectively replaced by +@option{-isysroot}, which you should use instead of @option{--sysroot}. +For other (non-Apple) versions of GCC, +if you use both this option and the @option{-isysroot} option, then +the @option{--sysroot} option will apply to libraries, but the +@option{-isysroot} option will apply to header files. + +The GNU linker (beginning with version 2.16) has the necessary support +for this option. If your linker does not support this option, the +header file aspect of @option{--sysroot} will still work, but the +library aspect will not. + +@item -I- +@opindex I- +This option has been deprecated. Please use @option{-iquote} instead for +@option{-I} directories before the @option{-I-} and remove the @option{-I-}. +Any directories you specify with @option{-I} options before the @option{-I-} +option are searched only for the case of @samp{#include "@var{file}"}; +they are not searched for @samp{#include <@var{file}>}. + +If additional directories are specified with @option{-I} options after +the @option{-I-}, these directories are searched for all @samp{#include} +directives. (Ordinarily @emph{all} @option{-I} directories are used +this way.) + +In addition, the @option{-I-} option inhibits the use of the current +directory (where the current input file came from) as the first search +directory for @samp{#include "@var{file}"}. There is no way to +override this effect of @option{-I-}. With @option{-I.} you can specify +searching the directory which was current when the compiler was +invoked. That is not exactly the same as what the preprocessor does +by default, but it is often satisfactory. + +@option{-I-} does not inhibit the use of the standard system directories +for header files. Thus, @option{-I-} and @option{-nostdinc} are +independent. +@end table + +@c man end + +@node Spec Files +@section Specifying subprocesses and the switches to pass to them +@cindex Spec Files + +@command{gcc} is a driver program. It performs its job by invoking a +sequence of other programs to do the work of compiling, assembling and +linking. GCC interprets its command-line parameters and uses these to +deduce which programs it should invoke, and which command-line options +it ought to place on their command lines. This behavior is controlled +by @dfn{spec strings}. In most cases there is one spec string for each +program that GCC can invoke, but a few programs have multiple spec +strings to control their behavior. The spec strings built into GCC can +be overridden by using the @option{-specs=} command-line switch to specify +a spec file. + +@dfn{Spec files} are plaintext files that are used to construct spec +strings. They consist of a sequence of directives separated by blank +lines. The type of directive is determined by the first non-whitespace +character on the line and it can be one of the following: + +@table @code +@item %@var{command} +Issues a @var{command} to the spec file processor. The commands that can +appear here are: + +@table @code +@item %include <@var{file}> +@cindex %include +Search for @var{file} and insert its text at the current point in the +specs file. + +@item %include_noerr <@var{file}> +@cindex %include_noerr +Just like @samp{%include}, but do not generate an error message if the include +file cannot be found. + +@item %rename @var{old_name} @var{new_name} +@cindex %rename +Rename the spec string @var{old_name} to @var{new_name}. + +@end table + +@item *[@var{spec_name}]: +This tells the compiler to create, override or delete the named spec +string. All lines after this directive up to the next directive or +blank line are considered to be the text for the spec string. If this +results in an empty string then the spec will be deleted. (Or, if the +spec did not exist, then nothing will happened.) Otherwise, if the spec +does not currently exist a new spec will be created. If the spec does +exist then its contents will be overridden by the text of this +directive, unless the first character of that text is the @samp{+} +character, in which case the text will be appended to the spec. + +@item [@var{suffix}]: +Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive +and up to the next directive or blank line are considered to make up the +spec string for the indicated suffix. When the compiler encounters an +input file with the named suffix, it will processes the spec string in +order to work out how to compile that file. For example: + +@smallexample +.ZZ: +z-compile -input %i +@end smallexample + +This says that any input file whose name ends in @samp{.ZZ} should be +passed to the program @samp{z-compile}, which should be invoked with the +command-line switch @option{-input} and with the result of performing the +@samp{%i} substitution. (See below.) + +As an alternative to providing a spec string, the text that follows a +suffix directive can be one of the following: + +@table @code +@item @@@var{language} +This says that the suffix is an alias for a known @var{language}. This is +similar to using the @option{-x} command-line switch to GCC to specify a +language explicitly. For example: + +@smallexample +.ZZ: +@@c++ +@end smallexample + +Says that .ZZ files are, in fact, C++ source files. + +@item #@var{name} +This causes an error messages saying: + +@smallexample +@var{name} compiler not installed on this system. +@end smallexample +@end table + +GCC already has an extensive list of suffixes built into it. +This directive will add an entry to the end of the list of suffixes, but +since the list is searched from the end backwards, it is effectively +possible to override earlier entries using this technique. + +@end table + +GCC has the following spec strings built into it. Spec files can +override these strings or create their own. Note that individual +targets can also add their own spec strings to this list. + +@smallexample +asm Options to pass to the assembler +asm_final Options to pass to the assembler post-processor +cpp Options to pass to the C preprocessor +cc1 Options to pass to the C compiler +cc1plus Options to pass to the C++ compiler +endfile Object files to include at the end of the link +link Options to pass to the linker +lib Libraries to include on the command line to the linker +libgcc Decides which GCC support library to pass to the linker +linker Sets the name of the linker +predefines Defines to be passed to the C preprocessor +signed_char Defines to pass to CPP to say whether @code{char} is signed + by default +startfile Object files to include at the start of the link +@end smallexample + +Here is a small example of a spec file: + +@smallexample +%rename lib old_lib + +*lib: +--start-group -lgcc -lc -leval1 --end-group %(old_lib) +@end smallexample + +This example renames the spec called @samp{lib} to @samp{old_lib} and +then overrides the previous definition of @samp{lib} with a new one. +The new definition adds in some extra command-line options before +including the text of the old definition. + +@dfn{Spec strings} are a list of command-line options to be passed to their +corresponding program. In addition, the spec strings can contain +@samp{%}-prefixed sequences to substitute variable text or to +conditionally insert text into the command line. Using these constructs +it is possible to generate quite complex command lines. + +Here is a table of all defined @samp{%}-sequences for spec +strings. Note that spaces are not generated automatically around the +results of expanding these sequences. Therefore you can concatenate them +together or combine them with constant text in a single argument. + +@table @code +@item %% +Substitute one @samp{%} into the program name or argument. + +@item %i +Substitute the name of the input file being processed. + +@item %b +Substitute the basename of the input file being processed. +This is the substring up to (and not including) the last period +and not including the directory. + +@item %B +This is the same as @samp{%b}, but include the file suffix (text after +the last period). + +@item %d +Marks the argument containing or following the @samp{%d} as a +temporary file name, so that that file will be deleted if GCC exits +successfully. Unlike @samp{%g}, this contributes no text to the +argument. + +@item %g@var{suffix} +Substitute a file name that has suffix @var{suffix} and is chosen +once per compilation, and mark the argument in the same way as +@samp{%d}. To reduce exposure to denial-of-service attacks, the file +name is now chosen in a way that is hard to predict even when previously +chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} +might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches +the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is +treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} +was simply substituted with a file name chosen once per compilation, +without regard to any appended suffix (which was therefore treated +just like ordinary text), making such attacks more likely to succeed. + +@item %u@var{suffix} +Like @samp{%g}, but generates a new temporary file name even if +@samp{%u@var{suffix}} was already seen. + +@item %U@var{suffix} +Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a +new one if there is no such last file name. In the absence of any +@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share +the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} +would involve the generation of two distinct file names, one +for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was +simply substituted with a file name chosen for the previous @samp{%u}, +without regard to any appended suffix. + +@item %j@var{suffix} +Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is +writable, and if save-temps is off; otherwise, substitute the name +of a temporary file, just like @samp{%u}. This temporary file is not +meant for communication between processes, but rather as a junk +disposal mechanism. + +@item %|@var{suffix} +@itemx %m@var{suffix} +Like @samp{%g}, except if @option{-pipe} is in effect. In that case +@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at +all. These are the two most common ways to instruct a program that it +should read from standard input or write to standard output. If you +need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} +construct: see for example @file{f/lang-specs.h}. + +@item %.@var{SUFFIX} +Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args +when it is subsequently output with @samp{%*}. @var{SUFFIX} is +terminated by the next space or %. + +@item %w +Marks the argument containing or following the @samp{%w} as the +designated output file of this compilation. This puts the argument +into the sequence of arguments that @samp{%o} will substitute later. + +@item %o +Substitutes the names of all the output files, with spaces +automatically placed around them. You should write spaces +around the @samp{%o} as well or the results are undefined. +@samp{%o} is for use in the specs for running the linker. +Input files whose names have no recognized suffix are not compiled +at all, but they are included among the output files, so they will +be linked. + +@item %O +Substitutes the suffix for object files. Note that this is +handled specially when it immediately follows @samp{%g, %u, or %U}, +because of the need for those to form complete file names. The +handling is such that @samp{%O} is treated exactly as if it had already +been substituted, except that @samp{%g, %u, and %U} do not currently +support additional @var{suffix} characters following @samp{%O} as they would +following, for example, @samp{.o}. + +@item %p +Substitutes the standard macro predefinitions for the +current target machine. Use this when running @code{cpp}. + +@item %P +Like @samp{%p}, but puts @samp{__} before and after the name of each +predefined macro, except for macros that start with @samp{__} or with +@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO +C@. + +@item %I +Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), +@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), +@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) +and @option{-imultilib} as necessary. + +@item %s +Current argument is the name of a library or startup file of some sort. +Search for that file in a standard list of directories and substitute +the full name found. + +@item %e@var{str} +Print @var{str} as an error message. @var{str} is terminated by a newline. +Use this when inconsistent options are detected. + +@item %(@var{name}) +Substitute the contents of spec string @var{name} at this point. + +@item %[@var{name}] +Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments. + +@item %x@{@var{option}@} +Accumulate an option for @samp{%X}. + +@item %X +Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} +spec string. + +@item %Y +Output the accumulated assembler options specified by @option{-Wa}. + +@item %Z +Output the accumulated preprocessor options specified by @option{-Wp}. + +@item %a +Process the @code{asm} spec. This is used to compute the +switches to be passed to the assembler. + +@item %A +Process the @code{asm_final} spec. This is a spec string for +passing switches to an assembler post-processor, if such a program is +needed. + +@item %l +Process the @code{link} spec. This is the spec for computing the +command line passed to the linker. Typically it will make use of the +@samp{%L %G %S %D and %E} sequences. + +@item %D +Dump out a @option{-L} option for each directory that GCC believes might +contain startup files. If the target supports multilibs then the +current multilib directory will be prepended to each of these paths. + +@item %L +Process the @code{lib} spec. This is a spec string for deciding which +libraries should be included on the command line to the linker. + +@item %G +Process the @code{libgcc} spec. This is a spec string for deciding +which GCC support library should be included on the command line to the linker. + +@item %S +Process the @code{startfile} spec. This is a spec for deciding which +object files should be the first ones passed to the linker. Typically +this might be a file named @file{crt0.o}. + +@item %E +Process the @code{endfile} spec. This is a spec string that specifies +the last object files that will be passed to the linker. + +@item %C +Process the @code{cpp} spec. This is used to construct the arguments +to be passed to the C preprocessor. + +@item %1 +Process the @code{cc1} spec. This is used to construct the options to be +passed to the actual C compiler (@samp{cc1}). + +@item %2 +Process the @code{cc1plus} spec. This is used to construct the options to be +passed to the actual C++ compiler (@samp{cc1plus}). + +@item %* +Substitute the variable part of a matched option. See below. +Note that each comma in the substituted string is replaced by +a single space. + +@item %<@code{S} +Remove all occurrences of @code{-S} from the command line. Note---this +command is position dependent. @samp{%} commands in the spec string +before this one will see @code{-S}, @samp{%} commands in the spec string +after this one will not. + +@item %:@var{function}(@var{args}) +Call the named function @var{function}, passing it @var{args}. +@var{args} is first processed as a nested spec string, then split +into an argument vector in the usual fashion. The function returns +a string which is processed as if it had appeared literally as part +of the current spec. + +The following built-in spec functions are provided: + +@table @code +@item @code{if-exists} +The @code{if-exists} spec function takes one argument, an absolute +pathname to a file. If the file exists, @code{if-exists} returns the +pathname. Here is a small example of its usage: + +@smallexample +*startfile: +crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s +@end smallexample + +@item @code{if-exists-else} +The @code{if-exists-else} spec function is similar to the @code{if-exists} +spec function, except that it takes two arguments. The first argument is +an absolute pathname to a file. If the file exists, @code{if-exists-else} +returns the pathname. If it does not exist, it returns the second argument. +This way, @code{if-exists-else} can be used to select one file or another, +based on the existence of the first. Here is a small example of its usage: + +@smallexample +*startfile: +crt0%O%s %:if-exists(crti%O%s) \ +%:if-exists-else(crtbeginT%O%s crtbegin%O%s) +@end smallexample + +@item @code{replace-outfile} +The @code{replace-outfile} spec function takes two arguments. It looks for the +first argument in the outfiles array and replaces it with the second argument. Here +is a small example of its usage: + +@smallexample +%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} +@end smallexample + +@end table + +@item %@{@code{S}@} +Substitutes the @code{-S} switch, if that switch was given to GCC@. +If that switch was not specified, this substitutes nothing. Note that +the leading dash is omitted when specifying this option, and it is +automatically inserted if the substitution is performed. Thus the spec +string @samp{%@{foo@}} would match the command-line option @option{-foo} +and would output the command line option @option{-foo}. + +@item %W@{@code{S}@} +Like %@{@code{S}@} but mark last argument supplied within as a file to be +deleted on failure. + +@item %@{@code{S}*@} +Substitutes all the switches specified to GCC whose names start +with @code{-S}, but which also take an argument. This is used for +switches like @option{-o}, @option{-D}, @option{-I}, etc. +GCC considers @option{-o foo} as being +one switch whose names starts with @samp{o}. %@{o*@} would substitute this +text, including the space. Thus two arguments would be generated. + +@item %@{@code{S}*&@code{T}*@} +Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options +(the order of @code{S} and @code{T} in the spec is not significant). +There can be any number of ampersand-separated variables; for each the +wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. + +@item %@{@code{S}:@code{X}@} +Substitutes @code{X}, if the @samp{-S} switch was given to GCC@. + +@item %@{!@code{S}:@code{X}@} +Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@. + +@item %@{@code{S}*:@code{X}@} +Substitutes @code{X} if one or more switches whose names start with +@code{-S} are specified to GCC@. Normally @code{X} is substituted only +once, no matter how many such switches appeared. However, if @code{%*} +appears somewhere in @code{X}, then @code{X} will be substituted once +for each matching switch, with the @code{%*} replaced by the part of +that switch that matched the @code{*}. + +@item %@{.@code{S}:@code{X}@} +Substitutes @code{X}, if processing a file with suffix @code{S}. + +@item %@{!.@code{S}:@code{X}@} +Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. + +@c APPLE LOCAL begin mainline 2007-03-13 5040758 +@item %@{,@code{S}:@code{X}@} +Substitutes @code{X}, if processing a file for language @code{S}. + +@item %@{!,@code{S}:@code{X}@} +Substitutes @code{X}, if not processing a file for language @code{S}. + +@item %@{@code{S}|@code{P}:@code{X}@} +Substitutes @code{X} if either @code{-S} or @code{-P} was given to +GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and +@code{*} sequences as well, although they have a stronger binding than +the @samp{|}. If @code{%*} appears in @code{X}, all of the +alternatives must be starred, and only the first matching alternative +is substituted. + +@c APPLE LOCAL end mainline 2007-03-13 5040758 +For example, a spec string like this: + +@smallexample +%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} +@end smallexample + +will output the following command-line options from the following input +command-line options: + +@smallexample +fred.c -foo -baz +jim.d -bar -boggle +-d fred.c -foo -baz -boggle +-d jim.d -bar -baz -boggle +@end smallexample + +@item %@{S:X; T:Y; :D@} + +@c APPLE LOCAL begin mainline 2007-03-13 5040758 +If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was +given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can +be as many clauses as you need. This may be combined with @code{.}, +@code{,}, @code{!}, @code{|}, and @code{*} as needed. +@c APPLE LOCAL end mainline 2007-03-13 5040758 + + +@end table + +The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar +construct may contain other nested @samp{%} constructs or spaces, or +even newlines. They are processed as usual, as described above. +Trailing white space in @code{X} is ignored. White space may also +appear anywhere on the left side of the colon in these constructs, +except between @code{.} or @code{*} and the corresponding word. + +The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are +handled specifically in these constructs. If another value of +@option{-O} or the negated form of a @option{-f}, @option{-m}, or +@option{-W} switch is found later in the command line, the earlier +switch value is ignored, except with @{@code{S}*@} where @code{S} is +just one letter, which passes all matching options. + +The character @samp{|} at the beginning of the predicate text is used to +indicate that a command should be piped to the following command, but +only if @option{-pipe} is specified. + +It is built into GCC which switches take arguments and which do not. +(You might think it would be useful to generalize this to allow each +compiler's spec to say which switches take arguments. But this cannot +be done in a consistent fashion. GCC cannot even decide which input +files have been specified without knowing which switches take arguments, +and it must know which input files to compile in order to tell which +compilers to run). + +GCC also knows implicitly that arguments starting in @option{-l} are to be +treated as compiler output files, and passed to the linker in their +proper position among the other output files. + +@c man begin OPTIONS + +@node Target Options +@section Specifying Target Machine and Compiler Version +@cindex target options +@cindex cross compiling +@cindex specifying machine version +@cindex specifying compiler version and target machine +@cindex compiler version, specifying +@cindex target machine, specifying + +The usual way to run GCC is to run the executable called @file{gcc}, or +@file{<machine>-gcc} when cross-compiling, or +@file{<machine>-gcc-<version>} to run a version other than the one that +was installed last. Sometimes this is inconvenient, so GCC provides +options that will switch to another cross-compiler or version. + +@table @gcctabopt +@item -b @var{machine} +@opindex b +The argument @var{machine} specifies the target machine for compilation. + +The value to use for @var{machine} is the same as was specified as the +machine type when configuring GCC as a cross-compiler. For +example, if a cross-compiler was configured with @samp{configure +arm-elf}, meaning to compile for an arm processor with elf binaries, +then you would specify @option{-b arm-elf} to run that cross compiler. +Because there are other options beginning with @option{-b}, the +configuration must contain a hyphen. + +@item -V @var{version} +@opindex V +The argument @var{version} specifies which version of GCC to run. +This is useful when multiple versions are installed. For example, +@var{version} might be @samp{4.0}, meaning to run GCC version 4.0. +@end table + +The @option{-V} and @option{-b} options work by running the +@file{<machine>-gcc-<version>} executable, so there's no real reason to +use them if you can just run that directly. + +@node Submodel Options +@section Hardware Models and Configurations +@cindex submodel options +@cindex specifying hardware config +@cindex hardware models and configurations, specifying +@cindex machine dependent options + +Earlier we discussed the standard option @option{-b} which chooses among +different installed compilers for completely different target +machines, such as VAX vs.@: 68000 vs.@: 80386. + +In addition, each of these target machine types can have its own +special options, starting with @samp{-m}, to choose among various +hardware models or configurations---for example, 68010 vs 68020, +floating coprocessor or none. A single installed version of the +compiler can compile for any model or configuration, according to the +options specified. + +Some configurations of the compiler also support additional special +options, usually for compatibility with other compilers on the same +platform. + +@c This list is ordered alphanumerically by subsection name. +@c It should be the same order and spelling as these options are listed +@c in Machine Dependent Options + +@menu +@c APPLE LOCAL prune man page +@ignore +* ARC Options:: +@c APPLE LOCAL ARM prune man page +@end ignore +* ARM Options:: +@c APPLE LOCAL ARM prune man page +@ignore +* AVR Options:: +* Blackfin Options:: +* CRIS Options:: +* CRX Options:: +@c APPLE LOCAL prune man page +@end ignore +* Darwin Options:: +@c APPLE LOCAL prune man page +@ignore +* DEC Alpha Options:: +* DEC Alpha/VMS Options:: +* FRV Options:: +* GNU/Linux Options:: +* H8/300 Options:: +* HPPA Options:: +@c APPLE LOCAL prune man page +@end ignore +* i386 and x86-64 Options:: +@c APPLE LOCAL prune man page +@ignore +* IA-64 Options:: +* M32C Options:: +* M32R/D Options:: +* M680x0 Options:: +* M68hc1x Options:: +* MCore Options:: +* MIPS Options:: +* MMIX Options:: +* MN10300 Options:: +* MT Options:: +* PDP-11 Options:: +@c APPLE LOCAL prune man page +@end ignore +* PowerPC Options:: +* RS/6000 and PowerPC Options:: +@c APPLE LOCAL prune man page +@ignore +* S/390 and zSeries Options:: +* Score Options:: +* SH Options:: +* SPARC Options:: +* System V Options:: +* TMS320C3x/C4x Options:: +* V850 Options:: +* VAX Options:: +* x86-64 Options:: +* Xstormy16 Options:: +* Xtensa Options:: +* zSeries Options:: +@c APPLE LOCAL prune man page +@end ignore +@end menu + +@c APPLE LOCAL prune man page +@ignore +@node ARC Options +@subsection ARC Options +@cindex ARC Options + +These options are defined for ARC implementations: + +@table @gcctabopt +@item -EL +@opindex EL +Compile code for little endian mode. This is the default. + +@item -EB +@opindex EB +Compile code for big endian mode. + +@item -mmangle-cpu +@opindex mmangle-cpu +Prepend the name of the cpu to all public symbol names. +In multiple-processor systems, there are many ARC variants with different +instruction and register set characteristics. This flag prevents code +compiled for one cpu to be linked with code compiled for another. +No facility exists for handling variants that are ``almost identical''. +This is an all or nothing option. + +@item -mcpu=@var{cpu} +@opindex mcpu +Compile code for ARC variant @var{cpu}. +Which variants are supported depend on the configuration. +All variants support @option{-mcpu=base}, this is the default. + +@item -mtext=@var{text-section} +@itemx -mdata=@var{data-section} +@itemx -mrodata=@var{readonly-data-section} +@opindex mtext +@opindex mdata +@opindex mrodata +Put functions, data, and readonly data in @var{text-section}, +@var{data-section}, and @var{readonly-data-section} respectively +by default. This can be overridden with the @code{section} attribute. +@xref{Variable Attributes}. + +@end table +@c APPLE LOCAL ARM prune man page +@end ignore + +@node ARM Options +@subsection ARM Options +@cindex ARM options + +These @samp{-m} options are defined for Advanced RISC Machines (ARM) +architectures: + +@table @gcctabopt +@item -mabi=@var{name} +@opindex mabi +Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, +@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. + +@item -mapcs-frame +@opindex mapcs-frame +Generate a stack frame that is compliant with the ARM Procedure Call +Standard for all functions, even if this is not strictly necessary for +correct execution of the code. Specifying @option{-fomit-frame-pointer} +with this option will cause the stack frames not to be generated for +leaf functions. The default is @option{-mno-apcs-frame}. + +@item -mapcs +@opindex mapcs +This is a synonym for @option{-mapcs-frame}. + +@c APPLE LOCAL We already have ignore running -- do not do this one --bowdidge +@c @ignore +@c not currently implemented +@item -mapcs-stack-check +@opindex mapcs-stack-check +Generate code to check the amount of stack space available upon entry to +every function (that actually uses some stack space). If there is +insufficient space available then either the function +@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be +called, depending upon the amount of stack space required. The run time +system is required to provide these functions. The default is +@option{-mno-apcs-stack-check}, since this produces smaller code. + +@c not currently implemented +@item -mapcs-float +@opindex mapcs-float +Pass floating point arguments using the float point registers. This is +one of the variants of the APCS@. This option is recommended if the +target hardware has a floating point unit or if a lot of floating point +arithmetic is going to be performed by the code. The default is +@option{-mno-apcs-float}, since integer only code is slightly increased in +size if @option{-mapcs-float} is used. + +@c not currently implemented +@item -mapcs-reentrant +@opindex mapcs-reentrant +Generate reentrant, position independent code. The default is +@option{-mno-apcs-reentrant}. +@c APPLE LOCAL We already have ignore running -- do not do this one --bowdidge +@c @end ignore + +@item -mthumb-interwork +@opindex mthumb-interwork +Generate code which supports calling between the ARM and Thumb +instruction sets. Without this option the two instruction sets cannot +be reliably used inside one program. The default is +@option{-mno-thumb-interwork}, since slightly larger code is generated +when @option{-mthumb-interwork} is specified. + +@item -mno-sched-prolog +@opindex mno-sched-prolog +Prevent the reordering of instructions in the function prolog, or the +merging of those instruction with the instructions in the function's +body. This means that all functions will start with a recognizable set +of instructions (or in fact one of a choice from a small set of +different function prologues), and this information can be used to +locate the start if functions inside an executable piece of code. The +default is @option{-msched-prolog}. + +@item -mhard-float +@opindex mhard-float +Generate output containing floating point instructions. This is the +default. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all ARM +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mfloat-abi=@var{name} +@opindex mfloat-abi +Specifies which ABI to use for floating point values. Permissible values +are: @samp{soft}, @samp{softfp} and @samp{hard}. + +@samp{soft} and @samp{hard} are equivalent to @option{-msoft-float} +and @option{-mhard-float} respectively. @samp{softfp} allows the generation +of floating point instructions, but still uses the soft-float calling +conventions. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. This is +the default for all standard configurations. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a processor running in big-endian mode; the default is +to compile code for a little-endian processor. + +@item -mwords-little-endian +@opindex mwords-little-endian +This option only applies when generating code for big-endian processors. +Generate code for a little-endian word order but a big-endian byte +order. That is, a byte order of the form @samp{32107654}. Note: this +option should only be used if you require compatibility with code for +big-endian ARM processors generated by versions of the compiler prior to +2.8. + +@item -mcpu=@var{name} +@opindex mcpu +This specifies the name of the target ARM processor. GCC uses this name +to determine what kind of instructions it can emit when generating +assembly code. Permissible names are: @samp{arm2}, @samp{arm250}, +@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, +@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, +@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, +@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, +@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s}, +@samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, +@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, +@samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s}, +@samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi}, +@samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s}, +@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, +@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, +@samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt}, +@samp{ep9312}. + +@itemx -mtune=@var{name} +@opindex mtune +This option is very similar to the @option{-mcpu=} option, except that +instead of specifying the actual target processor type, and hence +restricting which instructions can be used, it specifies that GCC should +tune the performance of the code as if the target were of the type +specified in this option, but still choosing the instructions that it +will generate based on the cpu specified by a @option{-mcpu=} option. +For some ARM implementations better performance can be obtained by using +this option. + +@item -march=@var{name} +@opindex march +This specifies the name of the target ARM architecture. GCC uses this +name to determine what kind of instructions it can emit when generating +assembly code. This option can be used in conjunction with or instead +of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, +@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, +@samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j}, +@samp{iwmmxt}, @samp{ep9312}. + +@item -mfpu=@var{name} +@itemx -mfpe=@var{number} +@itemx -mfp=@var{number} +@opindex mfpu +@opindex mfpe +@opindex mfp +This specifies what floating point hardware (or hardware emulation) is +available on the target. Permissible names are: @samp{fpa}, @samp{fpe2}, +@samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe} +are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility +with older versions of GCC@. + +If @option{-msoft-float} is specified this specifies the format of +floating point values. + +@item -mstructure-size-boundary=@var{n} +@opindex mstructure-size-boundary +The size of all structures and unions will be rounded up to a multiple +of the number of bits set by this option. Permissible values are 8, 32 +and 64. The default value varies for different toolchains. For the COFF +targeted toolchain the default value is 8. A value of 64 is only allowed +if the underlying ABI supports it. + +Specifying the larger number can produce faster, more efficient code, but +can also increase the size of the program. Different values are potentially +incompatible. Code compiled with one value cannot necessarily expect to +work with code or libraries compiled with another value, if they exchange +information using structures or unions. + +@item -mabort-on-noreturn +@opindex mabort-on-noreturn +Generate a call to the function @code{abort} at the end of a +@code{noreturn} function. It will be executed if the function tries to +return. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Tells the compiler to perform function calls by first loading the +address of the function into a register and then performing a subroutine +call on this register. This switch is needed if the target function +will lie outside of the 64 megabyte addressing range of the offset based +version of subroutine call instruction. + +Even if this switch is enabled, not all function calls will be turned +into long calls. The heuristic is that static functions, functions +which have the @samp{short-call} attribute, functions that are inside +the scope of a @samp{#pragma no_long_calls} directive and functions whose +definitions have already been compiled within the current compilation +unit, will not be turned into long calls. The exception to this rule is +that weak function definitions, functions with the @samp{long-call} +attribute or the @samp{section} attribute, and functions that are within +the scope of a @samp{#pragma long_calls} directive, will always be +turned into long calls. + +This feature is not enabled by default. Specifying +@option{-mno-long-calls} will restore the default behavior, as will +placing the function calls within the scope of a @samp{#pragma +long_calls_off} directive. Note these switches have no effect on how +the compiler generates code to handle function calls via function +pointers. + +@item -mnop-fun-dllimport +@opindex mnop-fun-dllimport +Disable support for the @code{dllimport} attribute. + +@item -msingle-pic-base +@opindex msingle-pic-base +Treat the register used for PIC addressing as read-only, rather than +loading it in the prologue for each function. The run-time system is +responsible for initializing this register with an appropriate value +before execution begins. + +@item -mpic-register=@var{reg} +@opindex mpic-register +Specify the register to be used for PIC addressing. The default is R10 +unless stack-checking is enabled, when R9 is used. + +@item -mcirrus-fix-invalid-insns +@opindex mcirrus-fix-invalid-insns +@opindex mno-cirrus-fix-invalid-insns +Insert NOPs into the instruction stream to in order to work around +problems with invalid Maverick instruction combinations. This option +is only valid if the @option{-mcpu=ep9312} option has been used to +enable generation of instructions for the Cirrus Maverick floating +point co-processor. This option is not enabled by default, since the +problem is only present in older Maverick implementations. The default +can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns} +switch. + +@item -mpoke-function-name +@opindex mpoke-function-name +Write the name of each function into the text section, directly +preceding the function prologue. The generated code is similar to this: + +@smallexample + t0 + .ascii "arm_poke_function_name", 0 + .align + t1 + .word 0xff000000 + (t1 - t0) + arm_poke_function_name + mov ip, sp + stmfd sp!, @{fp, ip, lr, pc@} + sub fp, ip, #4 +@end smallexample + +When performing a stack backtrace, code can inspect the value of +@code{pc} stored at @code{fp + 0}. If the trace function then looks at +location @code{pc - 12} and the top 8 bits are set, then we know that +there is a function name embedded immediately preceding this location +and has length @code{((pc[-3]) & 0xff000000)}. + +@c APPLE LOCAL begin v7 thumb is default +@item -mthumb +@opindex mthumb +Generate code for the 16-bit Thumb instruction set. For ARMv7, the default +is to use the THUMB2 instruction set. For all other architectures, the default +is to use the 32-bit ARM instruction set. The ARM instruction set may be +explicitly selected via @option{-mno-thumb} or @option{-marm}. +@c APPLE LOCAL end v7 thumb is default + +@item -mtpcs-frame +@opindex mtpcs-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all non-leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-tpcs-frame}. + +@item -mtpcs-leaf-frame +@opindex mtpcs-leaf-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. + +@item -mcallee-super-interworking +@opindex mcallee-super-interworking +Gives all externally visible functions in the file being compiled an ARM +instruction set header which switches to Thumb mode before executing the +rest of the function. This allows these functions to be called from +non-interworking code. + +@item -mcaller-super-interworking +@opindex mcaller-super-interworking +Allows calls via function pointers (including virtual functions) to +execute correctly regardless of whether the target code has been +compiled for interworking or not. There is a small overhead in the cost +of executing a function pointer if this option is enabled. + +@item -mtp=@var{name} +@opindex mtp +Specify the access model for the thread local storage pointer. The valid +models are @option{soft}, which generates calls to @code{__aeabi_read_tp}, +@option{cp15}, which fetches the thread pointer from @code{cp15} directly +(supported in the arm6k architecture), and @option{auto}, which uses the +best available method for the selected processor. The default setting is +@option{auto}. + +@c APPLE LOCAL begin 5946347 ms_struct support +@item -mms-bitfields +@opindex mms-bitfields +Set the default structure layout to be compatible with the Microsoft +compiler standard. This is equivalent to adding an @code{ms_struct} +attribute to each structure and union tag definition. The default is +@option{mno-ms-bitfields}. +@c APPLE LOCAL end 5946347 ms_struct support + +@end table + +@c APPLE LOCAL ARM prune man page +@ignore +@node AVR Options +@subsection AVR Options +@cindex AVR Options + +These options are defined for AVR implementations: + +@table @gcctabopt +@item -mmcu=@var{mcu} +@opindex mmcu +Specify ATMEL AVR instruction set or MCU type. + +Instruction set avr1 is for the minimal AVR core, not supported by the C +compiler, only for assembler programs (MCU types: at90s1200, attiny10, +attiny11, attiny12, attiny15, attiny28). + +Instruction set avr2 (default) is for the classic AVR core with up to +8K program memory space (MCU types: at90s2313, at90s2323, attiny22, +at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, +at90c8534, at90s8535). + +Instruction set avr3 is for the classic AVR core with up to 128K program +memory space (MCU types: atmega103, atmega603, at43usb320, at76c711). + +Instruction set avr4 is for the enhanced AVR core with up to 8K program +memory space (MCU types: atmega8, atmega83, atmega85). + +Instruction set avr5 is for the enhanced AVR core with up to 128K program +memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323, +atmega64, atmega128, at43usb355, at94k). + +@item -msize +@opindex msize +Output instruction sizes to the asm file. + +@item -minit-stack=@var{N} +@opindex minit-stack +Specify the initial stack address, which may be a symbol or numeric value, +@samp{__stack} is the default. + +@item -mno-interrupts +@opindex mno-interrupts +Generated code is not compatible with hardware interrupts. +Code size will be smaller. + +@item -mcall-prologues +@opindex mcall-prologues +Functions prologues/epilogues expanded as call to appropriate +subroutines. Code size will be smaller. + +@item -mno-tablejump +@opindex mno-tablejump +Do not generate tablejump insns which sometimes increase code size. + +@item -mtiny-stack +@opindex mtiny-stack +Change only the low 8 bits of the stack pointer. + +@item -mint8 +@opindex mint8 +Assume int to be 8 bit integer. This affects the sizes of all types: A +char will be 1 byte, an int will be 1 byte, an long will be 2 bytes +and long long will be 4 bytes. Please note that this option does not +comply to the C standards, but it will provide you with smaller code +size. +@end table + +@node Blackfin Options +@subsection Blackfin Options +@cindex Blackfin Options + +@table @gcctabopt +@item -momit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +Don't keep the frame pointer in a register for leaf functions. This +avoids the instructions to save, set up and restore frame pointers and +makes an extra register available in leaf functions. The option +@option{-fomit-frame-pointer} removes the frame pointer for all functions +which might make debugging harder. + +@item -mspecld-anomaly +@opindex mspecld-anomaly +When enabled, the compiler will ensure that the generated code does not +contain speculative loads after jump instructions. This option is enabled +by default. + +@item -mno-specld-anomaly +@opindex mno-specld-anomaly +Don't generate extra code to prevent speculative loads from occurring. + +@item -mcsync-anomaly +@opindex mcsync-anomaly +When enabled, the compiler will ensure that the generated code does not +contain CSYNC or SSYNC instructions too soon after conditional branches. +This option is enabled by default. + +@item -mno-csync-anomaly +@opindex mno-csync-anomaly +Don't generate extra code to prevent CSYNC or SSYNC instructions from +occurring too soon after a conditional branch. + +@item -mlow-64k +@opindex mlow-64k +When enabled, the compiler is free to take advantage of the knowledge that +the entire program fits into the low 64k of memory. + +@item -mno-low-64k +@opindex mno-low-64k +Assume that the program is arbitrarily large. This is the default. + +@item -mid-shared-library +@opindex mid-shared-library +Generate code that supports shared libraries via the library ID method. +This allows for execute in place and shared libraries in an environment +without virtual memory management. This option implies @option{-fPIC}. + +@item -mno-id-shared-library +@opindex mno-id-shared-library +Generate code that doesn't assume ID based shared libraries are being used. +This is the default. + +@item -mshared-library-id=n +@opindex mshared-library-id +Specified the identification number of the ID based shared library being +compiled. Specifying a value of 0 will generate more compact code, specifying +other values will force the allocation of that number to the current +library but is no more space or time efficient than omitting this option. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Tells the compiler to perform function calls by first loading the +address of the function into a register and then performing a subroutine +call on this register. This switch is needed if the target function +will lie outside of the 24 bit addressing range of the offset based +version of subroutine call instruction. + +This feature is not enabled by default. Specifying +@option{-mno-long-calls} will restore the default behavior. Note these +switches have no effect on how the compiler generates code to handle +function calls via function pointers. +@end table + +@node CRIS Options +@subsection CRIS Options +@cindex CRIS Options + +These options are defined specifically for the CRIS ports. + +@table @gcctabopt +@item -march=@var{architecture-type} +@itemx -mcpu=@var{architecture-type} +@opindex march +@opindex mcpu +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for +respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. +Default is @samp{v0} except for cris-axis-linux-gnu, where the default is +@samp{v10}. + +@item -mtune=@var{architecture-type} +@opindex mtune +Tune to @var{architecture-type} everything applicable about the generated +code, except for the ABI and the set of available instructions. The +choices for @var{architecture-type} are the same as for +@option{-march=@var{architecture-type}}. + +@item -mmax-stack-frame=@var{n} +@opindex mmax-stack-frame +Warn when the stack frame of a function exceeds @var{n} bytes. + +@item -melinux-stacksize=@var{n} +@opindex melinux-stacksize +Only available with the @samp{cris-axis-aout} target. Arranges for +indications in the program to the kernel loader that the stack of the +program should be set to @var{n} bytes. + +@item -metrax4 +@itemx -metrax100 +@opindex metrax4 +@opindex metrax100 +The options @option{-metrax4} and @option{-metrax100} are synonyms for +@option{-march=v3} and @option{-march=v8} respectively. + +@item -mmul-bug-workaround +@itemx -mno-mul-bug-workaround +@opindex mmul-bug-workaround +@opindex mno-mul-bug-workaround +Work around a bug in the @code{muls} and @code{mulu} instructions for CPU +models where it applies. This option is active by default. + +@item -mpdebug +@opindex mpdebug +Enable CRIS-specific verbose debug-related information in the assembly +code. This option also has the effect to turn off the @samp{#NO_APP} +formatted-code indicator to the assembler at the beginning of the +assembly file. + +@item -mcc-init +@opindex mcc-init +Do not use condition-code results from previous instruction; always emit +compare and test instructions before use of condition codes. + +@item -mno-side-effects +@opindex mno-side-effects +Do not emit instructions with side-effects in addressing modes other than +post-increment. + +@item -mstack-align +@itemx -mno-stack-align +@itemx -mdata-align +@itemx -mno-data-align +@itemx -mconst-align +@itemx -mno-const-align +@opindex mstack-align +@opindex mno-stack-align +@opindex mdata-align +@opindex mno-data-align +@opindex mconst-align +@opindex mno-const-align +These options (no-options) arranges (eliminate arrangements) for the +stack-frame, individual data and constants to be aligned for the maximum +single data access size for the chosen CPU model. The default is to +arrange for 32-bit alignment. ABI details such as structure layout are +not affected by these options. + +@item -m32-bit +@itemx -m16-bit +@itemx -m8-bit +@opindex m32-bit +@opindex m16-bit +@opindex m8-bit +Similar to the stack- data- and const-align options above, these options +arrange for stack-frame, writable data and constants to all be 32-bit, +16-bit or 8-bit aligned. The default is 32-bit alignment. + +@item -mno-prologue-epilogue +@itemx -mprologue-epilogue +@opindex mno-prologue-epilogue +@opindex mprologue-epilogue +With @option{-mno-prologue-epilogue}, the normal function prologue and +epilogue that sets up the stack-frame are omitted and no return +instructions or return sequences are generated in the code. Use this +option only together with visual inspection of the compiled code: no +warnings or errors are generated when call-saved registers must be saved, +or storage for local variable needs to be allocated. + +@item -mno-gotplt +@itemx -mgotplt +@opindex mno-gotplt +@opindex mgotplt +With @option{-fpic} and @option{-fPIC}, don't generate (do generate) +instruction sequences that load addresses for functions from the PLT part +of the GOT rather than (traditional on other architectures) calls to the +PLT@. The default is @option{-mgotplt}. + +@item -maout +@opindex maout +Legacy no-op option only recognized with the cris-axis-aout target. + +@item -melf +@opindex melf +Legacy no-op option only recognized with the cris-axis-elf and +cris-axis-linux-gnu targets. + +@item -melinux +@opindex melinux +Only recognized with the cris-axis-aout target, where it selects a +GNU/linux-like multilib, include files and instruction set for +@option{-march=v8}. + +@item -mlinux +@opindex mlinux +Legacy no-op option only recognized with the cris-axis-linux-gnu target. + +@item -sim +@opindex sim +This option, recognized for the cris-axis-aout and cris-axis-elf arranges +to link with input-output functions from a simulator library. Code, +initialized data and zero-initialized data are allocated consecutively. + +@item -sim2 +@opindex sim2 +Like @option{-sim}, but pass linker options to locate initialized data at +0x40000000 and zero-initialized data at 0x80000000. +@end table + +@node CRX Options +@subsection CRX Options +@cindex CRX Options + +These options are defined specifically for the CRX ports. + +@table @gcctabopt + +@item -mmac +@opindex mmac +Enable the use of multiply-accumulate instructions. Disabled by default. + +@item -mpush-args +@opindex mpush-args +Push instructions will be used to pass outgoing arguments when functions +are called. Enabled by default. +@end table +@c APPLE LOCAL prune man page +@end ignore + +@node Darwin Options +@subsection Darwin Options +@cindex Darwin options + +These options are defined for all architectures running the Darwin operating +system. + +@c APPLE LOCAL universal +FSF GCC on Darwin does not create ``universal'' object files; it will create +an object file for the single architecture that it was built to +@c APPLE LOCAL universal +target. Apple's GCC on Darwin does create ``universal'' files if multiple +@option{-arch} options are used; it does so by running the compiler or +linker multiple times and joining the results together with +@file{lipo}. + +The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or +@samp{i686}) is determined by the flags that specify the ISA +that GCC is targetting, like @option{-mcpu} or @option{-march}. The +@option{-force_cpusubtype_ALL} option can be used to override this. + +The Darwin tools vary in their behavior when presented with an ISA +mismatch. The assembler, @file{as}, will only permit instructions to +be used that are valid for the subtype of the file it is generating, +so you cannot put 64-bit instructions in an @samp{ppc750} object file. +The linker for shared libraries, @file{/usr/bin/libtool}, will fail +and print an error if asked to create a shared library with a less +restrictive subtype than its input files (for instance, trying to put +a @samp{ppc970} object file in a @samp{ppc7400} library). The linker +for executables, @file{ld}, will quietly give the executable the most +restrictive subtype of any of its input files. + +@table @gcctabopt +@item -F@var{dir} +@opindex F +Add the framework directory @var{dir} to the head of the list of +directories to be searched for header files. These directories are +interleaved with those specified by @option{-I} options and are +scanned in a left-to-right order. + +A framework directory is a directory with frameworks in it. A +framework is a directory with a @samp{"Headers"} and/or +@samp{"PrivateHeaders"} directory contained directly in it that ends +in @samp{".framework"}. The name of a framework is the name of this +directory excluding the @samp{".framework"}. Headers associated with +the framework are found in one of those two directories, with +@samp{"Headers"} being searched first. A subframework is a framework +directory that is in a framework's @samp{"Frameworks"} directory. +Includes of subframework headers can only appear in a header of a +framework that contains the subframework, or in a sibling subframework +header. Two subframeworks are siblings if they occur in the same +framework. A subframework should not have the same name as a +framework, a warning will be issued if this is violated. Currently a +subframework cannot have subframeworks, in the future, the mechanism +may be extended to support this. The standard frameworks can be found +in @samp{"/System/Library/Frameworks"} and +@samp{"/Library/Frameworks"}. An example include looks like +@code{#include <Framework/header.h>}, where @samp{Framework} denotes +the name of the framework and header.h is found in the +@samp{"PrivateHeaders"} or @samp{"Headers"} directory. + +@c APPLE LOCAL begin iframework for 4.3 4094959 +@item -iframework@var{dir} +@opindex iframework +Like @option{-F} except the directory is a treated as a system +directory. The main effect is to not warn about constructs contained +within header files found via @var{dir}. +@c APPLE LOCAL end iframework for 4.3 4094959 + +@item -gused +@opindex gused +Emit debugging information for symbols that are used. For STABS +debugging format, this enables @option{-feliminate-unused-debug-symbols}. +This is by default ON@. + +@item -gfull +@opindex gfull +Emit debugging information for all symbols and types. + +@item -mmacosx-version-min=@var{version} +The earliest version of MacOS X that this executable will run on +is @var{version}. Typical values of @var{version} include @code{10.1}, +@code{10.2}, and @code{10.3.9}. + +@c APPLE LOCAL begin ARM 5905142 +This value can also be set with the @env{MACOSX_DEPLOYMENT_TARGET} +environment variable. If both the command-line option is specified +and the environment variable is set, the command-line option will +take precedence. +@c APPLE LOCAL end ARM 5905142 + +@c APPLE LOCAL begin mainline 2007-06-14 5235474 +If the compiler was built to use the system's headers by default, +then the default for this option is the system version on which the +compiler is running, otherwise the default is to make choices which +are compatible with as many systems and code bases as possible. +@c APPLE LOCAL end mainline 2007-06-14 5235474 + +@c APPLE LOCAL begin ARM 5905142 +This value is not set by default for ARM targets. + +@item -miphoneos-version-min=@var{version} +The earliest version of iPhone OS that this executable will run on +is @var{version}. + +This value can also be set with the @env{IPHONEOS_DEPLOYMENT_TARGET} +environment variable. If both the command-line option is specified +and the environment variable is set, the command-line option will +take precedence. + +On ARM targets, if not specified by the command-line option or +environment variable, this value defaults to 2.0. +@c APPLE LOCAL end ARM 5905142 + +@item -mkernel +@opindex mkernel +Enable kernel development mode. The @option{-mkernel} option sets +@c APPLE LOCAL 5731065 +@option{-static}, @option{-fno-common}, @option{-fno-builtin}, @option{-fno-cxa-atexit}, +@c APPLE LOCAL 5628030 +@option{-fno-exceptions}, @option{-fno-non-call-exceptions}, @option{-fno-asynchronous-unwind-tables}, +@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where +applicable. This mode also sets @option{-mno-altivec}, +@c APPLE LOCAL begin 5731065 6268204 +@option{-msoft-float} and @option{-mlong-branch} for PowerPC targets, +@option{-mno-red-zone} on x86_64, and @option{-mlong-branch} for ARM +targets. Of these, only -msoft-float can be changed which is useful in +a kext that wishes to use the hardware floating point unit. +@c APPLE LOCAL end 5731065 6268204 +@c APPLE LOCAL begin kext weak_import 5935650 +@option{-dynamic} can be used to override the effects of -static on +the assembler to enable the use of weak_import. +@c APPLE LOCAL end kext weak_import 5935650 + +@item -mone-byte-bool +@opindex mone-byte-bool +Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}. +By default @samp{sizeof(bool)} is @samp{4} when compiling for +Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this +option has no effect on x86. + +@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC +to generate code that is not binary compatible with code generated +without that switch. Using this switch may require recompiling all +other modules in a program, including system libraries. Use this +switch to conform to a non-default data model. + +@item -mfix-and-continue +@itemx -ffix-and-continue +@itemx -findirect-data +@opindex mfix-and-continue +@opindex ffix-and-continue +@opindex findirect-data +Generate code suitable for fast turn around development. Needed to +enable gdb to dynamically load @code{.o} files into already running +programs. @option{-findirect-data} and @option{-ffix-and-continue} +are provided for backwards compatibility. + +@c APPLE LOCAL KEXT +@item -fapple-kext +@c APPLE LOCAL KEXT indirect-virtual-calls --sts +@itemx -findirect-virtual-calls +@c APPLE LOCAL KEXT terminated-vtables +@itemx -fterminated-vtables +@c APPLE LOCAL KEXT +@opindex fapple-kext +@c APPLE LOCAL KEXT indirect-virtual-calls --sts +@opindex findirect-virtual-calls +@c APPLE LOCAL KEXT terminated-vtables +@opindex fterminated-vtables +@c APPLE LOCAL begin KEXT +Alter vtables, destructors, and other implementation details to more +closely resemble the GCC 2.95 ABI for PowerPC and 32-bit i386. This +is to make kernel extensions loadable by Darwin kernels, and is +required to build any Darwin kernel extension. In addition, virtual +calls are not made directly, instead, code is generated to always go +through the virtual table, as virtual tables can be patched by the +kernel module loader. Vtables are altered by adding a zero word at +the end of every vtable. @option{-findirect-virtual-calls} and +@option{-fterminated-vtables} are accepted for backwards compatibility +but will be removed in the future. Additionally implies +most of @option{-mkernel} except for @option{-msoft-float} and +@option{-mlong-branch} for PowerPC targets. (APPLE ONLY) +@c APPLE LOCAL end KEXT + +@c APPLE LOCAL begin pascal strings +@item -mpascal-strings +Allow Pascal-style string literals to be constructed. This option +implies @option{-Wpointer-sign} so that conversions between +Pascal-style strings and C-style strings are warned about. (APPLE +ONLY) + +@xref{Pascal Strings,,Constructing String Literals with a Pascal-style +Length Byte}, for more information on the syntax and semantics of Pascal +string literals. +@c APPLE LOCAL end pascal strings + +@item -all_load +@opindex all_load +Loads all members of static archive libraries. +See man ld(1) for more information. + +@item -arch_errors_fatal +@opindex arch_errors_fatal +Cause the errors having to do with files that have the wrong architecture +to be fatal. + +@item -bind_at_load +@opindex bind_at_load +Causes the output file to be marked such that the dynamic linker will +bind all undefined references when the file is loaded or launched. + +@item -bundle +@opindex bundle +Produce a Mach-o bundle format file. +See man ld(1) for more information. + +@item -bundle_loader @var{executable} +@opindex bundle_loader +This option specifies the @var{executable} that will be loading the build +output file being linked. See man ld(1) for more information. + +@item -dynamiclib +@opindex dynamiclib +When passed this option, GCC will produce a dynamic library instead of +an executable when linking, using the Darwin @file{libtool} command. + +@item -force_cpusubtype_ALL +@opindex force_cpusubtype_ALL +This causes GCC's output file to have the @var{ALL} subtype, instead of +one controlled by the @option{-mcpu} or @option{-march} option. + +@c APPLE LOCAL begin 7519550 force local +@item -force_load @var{library_name} +@opindex force_load +Loads all members of named static archive library. +See man ld(1) for more information. +@c APPLE LOCAL end 7519550 force local + +@item -allowable_client @var{client_name} +@itemx -client_name +@itemx -compatibility_version +@itemx -current_version +@itemx -dead_strip +@itemx -dependency-file +@itemx -dylib_file +@itemx -dylinker_install_name +@itemx -dynamic +@itemx -exported_symbols_list +@itemx -filelist +@itemx -flat_namespace +@itemx -force_flat_namespace +@itemx -headerpad_max_install_names +@itemx -image_base +@itemx -init +@itemx -install_name +@itemx -keep_private_externs +@itemx -multi_module +@itemx -multiply_defined +@itemx -multiply_defined_unused +@itemx -noall_load +@itemx -no_dead_strip_inits_and_terms +@itemx -nofixprebinding +@itemx -nomultidefs +@itemx -noprebind +@itemx -noseglinkedit +@itemx -pagezero_size +@itemx -prebind +@itemx -prebind_all_twolevel_modules +@itemx -private_bundle +@itemx -read_only_relocs +@itemx -sectalign +@itemx -sectobjectsymbols +@itemx -whyload +@itemx -seg1addr +@itemx -sectcreate +@itemx -sectobjectsymbols +@itemx -sectorder +@itemx -segaddr +@itemx -segs_read_only_addr +@itemx -segs_read_write_addr +@itemx -seg_addr_table +@itemx -seg_addr_table_filename +@itemx -seglinkedit +@itemx -segprot +@itemx -segs_read_only_addr +@itemx -segs_read_write_addr +@itemx -single_module +@itemx -static +@itemx -sub_library +@itemx -sub_umbrella +@itemx -twolevel_namespace +@itemx -umbrella +@itemx -undefined +@itemx -unexported_symbols_list +@itemx -weak_reference_mismatches +@itemx -whatsloaded + +@opindex allowable_client +@opindex client_name +@opindex compatibility_version +@opindex current_version +@opindex dead_strip +@opindex dependency-file +@opindex dylib_file +@opindex dylinker_install_name +@opindex dynamic +@opindex exported_symbols_list +@opindex filelist +@opindex flat_namespace +@opindex force_flat_namespace +@opindex headerpad_max_install_names +@opindex image_base +@opindex init +@opindex install_name +@opindex keep_private_externs +@opindex multi_module +@opindex multiply_defined +@opindex multiply_defined_unused +@opindex noall_load +@opindex no_dead_strip_inits_and_terms +@opindex nofixprebinding +@opindex nomultidefs +@opindex noprebind +@opindex noseglinkedit +@opindex pagezero_size +@opindex prebind +@opindex prebind_all_twolevel_modules +@opindex private_bundle +@opindex read_only_relocs +@opindex sectalign +@opindex sectobjectsymbols +@opindex whyload +@opindex seg1addr +@opindex sectcreate +@opindex sectobjectsymbols +@opindex sectorder +@opindex segaddr +@opindex segs_read_only_addr +@opindex segs_read_write_addr +@opindex seg_addr_table +@opindex seg_addr_table_filename +@opindex seglinkedit +@opindex segprot +@opindex segs_read_only_addr +@opindex segs_read_write_addr +@opindex single_module +@opindex static +@opindex sub_library +@opindex sub_umbrella +@opindex twolevel_namespace +@opindex umbrella +@opindex undefined +@opindex unexported_symbols_list +@opindex weak_reference_mismatches +@opindex whatsloaded + +These options are passed to the Darwin linker. The Darwin linker man page +describes them in detail. +@end table + +@c APPLE LOCAL prune man page +@ignore +@node DEC Alpha Options +@subsection DEC Alpha Options + +These @samp{-m} options are defined for the DEC Alpha implementations: + +@table @gcctabopt +@item -mno-soft-float +@itemx -msoft-float +@opindex mno-soft-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions for +floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} will be used to perform floating-point +operations. Unless they are replaced by routines that emulate the +floating-point operations, or compiled in such a way as to call such +emulations routines, these routines will issue floating-point +operations. If you are compiling for an Alpha without floating-point +operations, you must ensure that the library is built so as not to call +them. + +Note that Alpha implementations without floating-point operations are +required to have floating-point registers. + +@item -mfp-reg +@itemx -mno-fp-regs +@opindex mfp-reg +@opindex mno-fp-regs +Generate code that uses (does not use) the floating-point register set. +@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point +register set is not used, floating point operands are passed in integer +registers as if they were integers and floating-point results are passed +in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, +so any function with a floating-point argument or return value called by code +compiled with @option{-mno-fp-regs} must also be compiled with that +option. + +A typical use of this option is building a kernel that does not use, +and hence need not save and restore, any floating-point registers. + +@item -mieee +@opindex mieee +The Alpha architecture implements floating-point hardware optimized for +maximum performance. It is mostly compliant with the IEEE floating +point standard. However, for full compliance, software assistance is +required. This option generates code fully IEEE compliant code +@emph{except} that the @var{inexact-flag} is not maintained (see below). +If this option is turned on, the preprocessor macro @code{_IEEE_FP} is +defined during compilation. The resulting code is less efficient but is +able to correctly support denormalized numbers and exceptional IEEE +values such as not-a-number and plus/minus infinity. Other Alpha +compilers call this option @option{-ieee_with_no_inexact}. + +@item -mieee-with-inexact +@opindex mieee-with-inexact +This is like @option{-mieee} except the generated code also maintains +the IEEE @var{inexact-flag}. Turning on this option causes the +generated code to implement fully-compliant IEEE math. In addition to +@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor +macro. On some Alpha implementations the resulting code may execute +significantly slower than the code generated by default. Since there is +very little code that depends on the @var{inexact-flag}, you should +normally not specify this option. Other Alpha compilers call this +option @option{-ieee_with_inexact}. + +@item -mfp-trap-mode=@var{trap-mode} +@opindex mfp-trap-mode +This option controls what floating-point related traps are enabled. +Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. +The trap mode can be set to one of four values: + +@table @samp +@item n +This is the default (normal) setting. The only traps that are enabled +are the ones that cannot be disabled in software (e.g., division by zero +trap). + +@item u +In addition to the traps enabled by @samp{n}, underflow traps are enabled +as well. + +@item su +Like @samp{u}, but the instructions are marked to be safe for software +completion (see Alpha architecture manual for details). + +@item sui +Like @samp{su}, but inexact traps are enabled as well. +@end table + +@item -mfp-rounding-mode=@var{rounding-mode} +@opindex mfp-rounding-mode +Selects the IEEE rounding mode. Other Alpha compilers call this option +@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one +of: + +@table @samp +@item n +Normal IEEE rounding mode. Floating point numbers are rounded towards +the nearest machine number or towards the even machine number in case +of a tie. + +@item m +Round towards minus infinity. + +@item c +Chopped rounding mode. Floating point numbers are rounded towards zero. + +@item d +Dynamic rounding mode. A field in the floating point control register +(@var{fpcr}, see Alpha architecture reference manual) controls the +rounding mode in effect. The C library initializes this register for +rounding towards plus infinity. Thus, unless your program modifies the +@var{fpcr}, @samp{d} corresponds to round towards plus infinity. +@end table + +@item -mtrap-precision=@var{trap-precision} +@opindex mtrap-precision +In the Alpha architecture, floating point traps are imprecise. This +means without software assistance it is impossible to recover from a +floating trap and program execution normally needs to be terminated. +GCC can generate code that can assist operating system trap handlers +in determining the exact location that caused a floating point trap. +Depending on the requirements of an application, different levels of +precisions can be selected: + +@table @samp +@item p +Program precision. This option is the default and means a trap handler +can only identify which program caused a floating point exception. + +@item f +Function precision. The trap handler can determine the function that +caused a floating point exception. + +@item i +Instruction precision. The trap handler can determine the exact +instruction that caused a floating point exception. +@end table + +Other Alpha compilers provide the equivalent options called +@option{-scope_safe} and @option{-resumption_safe}. + +@item -mieee-conformant +@opindex mieee-conformant +This option marks the generated code as IEEE conformant. You must not +use this option unless you also specify @option{-mtrap-precision=i} and either +@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect +is to emit the line @samp{.eflag 48} in the function prologue of the +generated assembly file. Under DEC Unix, this has the effect that +IEEE-conformant math library routines will be linked in. + +@item -mbuild-constants +@opindex mbuild-constants +Normally GCC examines a 32- or 64-bit integer constant to +see if it can construct it from smaller constants in two or three +instructions. If it cannot, it will output the constant as a literal and +generate code to load it from the data segment at runtime. + +Use this option to require GCC to construct @emph{all} integer constants +using code, even if it takes more instructions (the maximum is six). + +You would typically use this option to build a shared library dynamic +loader. Itself a shared library, it must relocate itself in memory +before it can find the variables and constants in its own data segment. + +@item -malpha-as +@itemx -mgas +@opindex malpha-as +@opindex mgas +Select whether to generate code to be assembled by the vendor-supplied +assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}. + +@item -mbwx +@itemx -mno-bwx +@itemx -mcix +@itemx -mno-cix +@itemx -mfix +@itemx -mno-fix +@itemx -mmax +@itemx -mno-max +@opindex mbwx +@opindex mno-bwx +@opindex mcix +@opindex mno-cix +@opindex mfix +@opindex mno-fix +@opindex mmax +@opindex mno-max +Indicate whether GCC should generate code to use the optional BWX, +CIX, FIX and MAX instruction sets. The default is to use the instruction +sets supported by the CPU type specified via @option{-mcpu=} option or that +of the CPU on which GCC was built if none was specified. + +@item -mfloat-vax +@itemx -mfloat-ieee +@opindex mfloat-vax +@opindex mfloat-ieee +Generate code that uses (does not use) VAX F and G floating point +arithmetic instead of IEEE single and double precision. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Older Alpha assemblers provided no way to generate symbol relocations +except via assembler macros. Use of these macros does not allow +optimal instruction scheduling. GNU binutils as of version 2.12 +supports a new syntax that allows the compiler to explicitly mark +which relocations should apply to which instructions. This option +is mostly useful for debugging, as GCC detects the capabilities of +the assembler when it is built and sets the default accordingly. + +@item -msmall-data +@itemx -mlarge-data +@opindex msmall-data +@opindex mlarge-data +When @option{-mexplicit-relocs} is in effect, static data is +accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} +is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} +(the @code{.sdata} and @code{.sbss} sections) and are accessed via +16-bit relocations off of the @code{$gp} register. This limits the +size of the small data area to 64KB, but allows the variables to be +directly accessed via a single instruction. + +The default is @option{-mlarge-data}. With this option the data area +is limited to just below 2GB@. Programs that require more than 2GB of +data must use @code{malloc} or @code{mmap} to allocate the data in the +heap instead of in the program's data segment. + +When generating code for shared libraries, @option{-fpic} implies +@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. + +@item -msmall-text +@itemx -mlarge-text +@opindex msmall-text +@opindex mlarge-text +When @option{-msmall-text} is used, the compiler assumes that the +code of the entire program (or shared library) fits in 4MB, and is +thus reachable with a branch instruction. When @option{-msmall-data} +is used, the compiler can assume that all local symbols share the +same @code{$gp} value, and thus reduce the number of instructions +required for a function call from 4 to 1. + +The default is @option{-mlarge-text}. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set and instruction scheduling parameters for +machine type @var{cpu_type}. You can specify either the @samp{EV} +style name or the corresponding chip number. GCC supports scheduling +parameters for the EV4, EV5 and EV6 family of processors and will +choose the default values for the instruction set from the processor +you specify. If you do not specify a processor type, GCC will default +to the processor on which the compiler was built. + +Supported values for @var{cpu_type} are + +@table @samp +@item ev4 +@itemx ev45 +@itemx 21064 +Schedules as an EV4 and has no instruction set extensions. + +@item ev5 +@itemx 21164 +Schedules as an EV5 and has no instruction set extensions. + +@item ev56 +@itemx 21164a +Schedules as an EV5 and supports the BWX extension. + +@item pca56 +@itemx 21164pc +@itemx 21164PC +Schedules as an EV5 and supports the BWX and MAX extensions. + +@item ev6 +@itemx 21264 +Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. + +@item ev67 +@itemx 21264a +Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. +@end table + +@item -mtune=@var{cpu_type} +@opindex mtune +Set only the instruction scheduling parameters for machine type +@var{cpu_type}. The instruction set is not changed. + +@item -mmemory-latency=@var{time} +@opindex mmemory-latency +Sets the latency the scheduler should assume for typical memory +references as seen by the application. This number is highly +dependent on the memory access patterns used by the application +and the size of the external cache on the machine. + +Valid options for @var{time} are + +@table @samp +@item @var{number} +A decimal number representing clock cycles. + +@item L1 +@itemx L2 +@itemx L3 +@itemx main +The compiler contains estimates of the number of clock cycles for +``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches +(also called Dcache, Scache, and Bcache), as well as to main memory. +Note that L3 is only valid for EV5. + +@end table +@end table + +@node DEC Alpha/VMS Options +@subsection DEC Alpha/VMS Options + +These @samp{-m} options are defined for the DEC Alpha/VMS implementations: + +@table @gcctabopt +@item -mvms-return-codes +@opindex mvms-return-codes +Return VMS condition codes from main. The default is to return POSIX +style condition (e.g.@ error) codes. +@end table + +@node FRV Options +@subsection FRV Options +@cindex FRV Options + +@table @gcctabopt +@item -mgpr-32 +@opindex mgpr-32 + +Only use the first 32 general purpose registers. + +@item -mgpr-64 +@opindex mgpr-64 + +Use all 64 general purpose registers. + +@item -mfpr-32 +@opindex mfpr-32 + +Use only the first 32 floating point registers. + +@item -mfpr-64 +@opindex mfpr-64 + +Use all 64 floating point registers + +@item -mhard-float +@opindex mhard-float + +Use hardware instructions for floating point operations. + +@item -msoft-float +@opindex msoft-float + +Use library routines for floating point operations. + +@item -malloc-cc +@opindex malloc-cc + +Dynamically allocate condition code registers. + +@item -mfixed-cc +@opindex mfixed-cc + +Do not try to dynamically allocate condition code registers, only +use @code{icc0} and @code{fcc0}. + +@item -mdword +@opindex mdword + +Change ABI to use double word insns. + +@item -mno-dword +@opindex mno-dword + +Do not use double word instructions. + +@item -mdouble +@opindex mdouble + +Use floating point double instructions. + +@item -mno-double +@opindex mno-double + +Do not use floating point double instructions. + +@item -mmedia +@opindex mmedia + +Use media instructions. + +@item -mno-media +@opindex mno-media + +Do not use media instructions. + +@item -mmuladd +@opindex mmuladd + +Use multiply and add/subtract instructions. + +@item -mno-muladd +@opindex mno-muladd + +Do not use multiply and add/subtract instructions. + +@item -mfdpic +@opindex mfdpic + +Select the FDPIC ABI, that uses function descriptors to represent +pointers to functions. Without any PIC/PIE-related options, it +implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it +assumes GOT entries and small data are within a 12-bit range from the +GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets +are computed with 32 bits. + +@item -minline-plt +@opindex minline-plt + +Enable inlining of PLT entries in function calls to functions that are +not known to bind locally. It has no effect without @option{-mfdpic}. +It's enabled by default if optimizing for speed and compiling for +shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an +optimization option such as @option{-O3} or above is present in the +command line. + +@item -mTLS +@opindex TLS + +Assume a large TLS segment when generating thread-local code. + +@item -mtls +@opindex tls + +Do not assume a large TLS segment when generating thread-local code. + +@item -mgprel-ro +@opindex mgprel-ro + +Enable the use of @code{GPREL} relocations in the FDPIC ABI for data +that is known to be in read-only sections. It's enabled by default, +except for @option{-fpic} or @option{-fpie}: even though it may help +make the global offset table smaller, it trades 1 instruction for 4. +With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, +one of which may be shared by multiple symbols, and it avoids the need +for a GOT entry for the referenced symbol, so it's more likely to be a +win. If it is not, @option{-mno-gprel-ro} can be used to disable it. + +@item -multilib-library-pic +@opindex multilib-library-pic + +Link with the (library, not FD) pic libraries. It's implied by +@option{-mlibrary-pic}, as well as by @option{-fPIC} and +@option{-fpic} without @option{-mfdpic}. You should never have to use +it explicitly. + +@item -mlinked-fp +@opindex mlinked-fp + +Follow the EABI requirement of always creating a frame pointer whenever +a stack frame is allocated. This option is enabled by default and can +be disabled with @option{-mno-linked-fp}. + +@item -mlong-calls +@opindex mlong-calls + +Use indirect addressing to call functions outside the current +compilation unit. This allows the functions to be placed anywhere +within the 32-bit address space. + +@item -malign-labels +@opindex malign-labels + +Try to align labels to an 8-byte boundary by inserting nops into the +previous packet. This option only has an effect when VLIW packing +is enabled. It doesn't create new packets; it merely adds nops to +existing ones. + +@item -mlibrary-pic +@opindex mlibrary-pic + +Generate position-independent EABI code. + +@item -macc-4 +@opindex macc-4 + +Use only the first four media accumulator registers. + +@item -macc-8 +@opindex macc-8 + +Use all eight media accumulator registers. + +@item -mpack +@opindex mpack + +Pack VLIW instructions. + +@item -mno-pack +@opindex mno-pack + +Do not pack VLIW instructions. + +@item -mno-eflags +@opindex mno-eflags + +Do not mark ABI switches in e_flags. + +@item -mcond-move +@opindex mcond-move + +Enable the use of conditional-move instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-cond-move +@opindex mno-cond-move + +Disable the use of conditional-move instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mscc +@opindex mscc + +Enable the use of conditional set instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-scc +@opindex mno-scc + +Disable the use of conditional set instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mcond-exec +@opindex mcond-exec + +Enable the use of conditional execution (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-cond-exec +@opindex mno-cond-exec + +Disable the use of conditional execution. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mvliw-branch +@opindex mvliw-branch + +Run a pass to pack branches into VLIW instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-vliw-branch +@opindex mno-vliw-branch + +Do not run a pass to pack branches into VLIW instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mmulti-cond-exec +@opindex mmulti-cond-exec + +Enable optimization of @code{&&} and @code{||} in conditional execution +(default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-multi-cond-exec +@opindex mno-multi-cond-exec + +Disable optimization of @code{&&} and @code{||} in conditional execution. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mnested-cond-exec +@opindex mnested-cond-exec + +Enable nested conditional execution optimizations (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-nested-cond-exec +@opindex mno-nested-cond-exec + +Disable nested conditional execution optimizations. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -moptimize-membar +@opindex moptimize-membar + +This switch removes redundant @code{membar} instructions from the +compiler generated code. It is enabled by default. + +@item -mno-optimize-membar +@opindex mno-optimize-membar + +This switch disables the automatic removal of redundant @code{membar} +instructions from the generated code. + +@item -mtomcat-stats +@opindex mtomcat-stats + +Cause gas to print out tomcat statistics. + +@item -mcpu=@var{cpu} +@opindex mcpu + +Select the processor type for which to generate code. Possible values are +@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, +@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. + +@end table + +@node GNU/Linux Options +@subsection GNU/Linux Options + +These @samp{-m} options are defined for GNU/Linux targets: + +@table @gcctabopt +@item -mglibc +@opindex mglibc +Use the GNU C library instead of uClibc. This is the default except +on @samp{*-*-linux-*uclibc*} targets. + +@item -muclibc +@opindex muclibc +Use uClibc instead of the GNU C library. This is the default on +@samp{*-*-linux-*uclibc*} targets. +@end table + +@node H8/300 Options +@subsection H8/300 Options + +These @samp{-m} options are defined for the H8/300 implementations: + +@table @gcctabopt +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, +ld, Using ld}, for a fuller description. + +@item -mh +@opindex mh +Generate code for the H8/300H@. + +@item -ms +@opindex ms +Generate code for the H8S@. + +@item -mn +@opindex mn +Generate code for the H8S and H8/300H in the normal mode. This switch +must be used either with @option{-mh} or @option{-ms}. + +@item -ms2600 +@opindex ms2600 +Generate code for the H8S/2600. This switch must be used with @option{-ms}. + +@item -mint32 +@opindex mint32 +Make @code{int} data 32 bits by default. + +@item -malign-300 +@opindex malign-300 +On the H8/300H and H8S, use the same alignment rules as for the H8/300. +The default for the H8/300H and H8S is to align longs and floats on 4 +byte boundaries. +@option{-malign-300} causes them to be aligned on 2 byte boundaries. +This option has no effect on the H8/300. +@end table + +@node HPPA Options +@subsection HPPA Options +@cindex HPPA Options + +These @samp{-m} options are defined for the HPPA family of computers: + +@table @gcctabopt +@item -march=@var{architecture-type} +@opindex march +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA +1.1, and @samp{2.0} for PA 2.0 processors. Refer to +@file{/usr/lib/sched.models} on an HP-UX system to determine the proper +architecture option for your machine. Code compiled for lower numbered +architectures will run on higher numbered architectures, but not the +other way around. + +@item -mpa-risc-1-0 +@itemx -mpa-risc-1-1 +@itemx -mpa-risc-2-0 +@opindex mpa-risc-1-0 +@opindex mpa-risc-1-1 +@opindex mpa-risc-2-0 +Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. + +@item -mbig-switch +@opindex mbig-switch +Generate code suitable for big switch tables. Use this option only if +the assembler/linker complain about out of range branches within a switch +table. + +@item -mjump-in-delay +@opindex mjump-in-delay +Fill delay slots of function calls with unconditional jump instructions +by modifying the return pointer for the function call to be the target +of the conditional jump. + +@item -mdisable-fpregs +@opindex mdisable-fpregs +Prevent floating point registers from being used in any manner. This is +necessary for compiling kernels which perform lazy context switching of +floating point registers. If you use this option and attempt to perform +floating point operations, the compiler will abort. + +@item -mdisable-indexing +@opindex mdisable-indexing +Prevent the compiler from using indexing address modes. This avoids some +rather obscure problems when compiling MIG generated code under MACH@. + +@item -mno-space-regs +@opindex mno-space-regs +Generate code that assumes the target has no space registers. This allows +GCC to generate faster indirect calls and use unscaled index address modes. + +Such code is suitable for level 0 PA systems and kernels. + +@item -mfast-indirect-calls +@opindex mfast-indirect-calls +Generate code that assumes calls never cross space boundaries. This +allows GCC to emit code which performs faster indirect calls. + +This option will not work in the presence of shared libraries or nested +functions. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator can not use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. + +@item -mlong-load-store +@opindex mlong-load-store +Generate 3-instruction load and store sequences as sometimes required by +the HP-UX 10 linker. This is equivalent to the @samp{+k} option to +the HP compilers. + +@item -mportable-runtime +@opindex mportable-runtime +Use the portable calling conventions proposed by HP for ELF systems. + +@item -mgas +@opindex mgas +Enable the use of assembler directives only GAS understands. + +@item -mschedule=@var{cpu-type} +@opindex mschedule +Schedule code according to the constraints for the machine type +@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} +@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer +to @file{/usr/lib/sched.models} on an HP-UX system to determine the +proper scheduling option for your machine. The default scheduling is +@samp{8000}. + +@item -mlinker-opt +@opindex mlinker-opt +Enable the optimization pass in the HP-UX linker. Note this makes symbolic +debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 +linkers in which they give bogus error messages when linking some programs. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all HPPA +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. The embedded target @samp{hppa1.1-*-pro} +does provide software floating point support. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -msio +@opindex msio +Generate the predefine, @code{_SIO}, for server IO@. The default is +@option{-mwsio}. This generates the predefines, @code{__hp9000s700}, +@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These +options are available under HP-UX and HI-UX@. + +@item -mgnu-ld +@opindex gnu-ld +Use GNU ld specific options. This passes @option{-shared} to ld when +building a shared library. It is the default when GCC is configured, +explicitly or implicitly, with the GNU linker. This option does not +have any affect on which ld is called, it only changes what parameters +are passed to that ld. The ld that is called is determined by the +@option{--with-ld} configure option, GCC's program search path, and +finally by the user's @env{PATH}. The linker used by GCC can be printed +using @samp{which `gcc -print-prog-name=ld`}. This option is only available +on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}. + +@item -mhp-ld +@opindex hp-ld +Use HP ld specific options. This passes @option{-b} to ld when building +a shared library and passes @option{+Accept TypeMismatch} to ld on all +links. It is the default when GCC is configured, explicitly or +implicitly, with the HP linker. This option does not have any affect on +which ld is called, it only changes what parameters are passed to that +ld. The ld that is called is determined by the @option{--with-ld} +configure option, GCC's program search path, and finally by the user's +@env{PATH}. The linker used by GCC can be printed using @samp{which +`gcc -print-prog-name=ld`}. This option is only available on the 64 bit +HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}. + +@item -mlong-calls +@opindex mno-long-calls +Generate code that uses long call sequences. This ensures that a call +is always able to reach linker generated stubs. The default is to generate +long calls only when the distance from the call site to the beginning +of the function or translation unit, as the case may be, exceeds a +predefined limit set by the branch type being used. The limits for +normal calls are 7,600,000 and 240,000 bytes, respectively for the +PA 2.0 and PA 1.X architectures. Sibcalls are always limited at +240,000 bytes. + +Distances are measured from the beginning of functions when using the +@option{-ffunction-sections} option, or when using the @option{-mgas} +and @option{-mno-portable-runtime} options together under HP-UX with +the SOM linker. + +It is normally not desirable to use this option as it will degrade +performance. However, it may be useful in large applications, +particularly when partial linking is used to build the application. + +The types of long calls used depends on the capabilities of the +assembler and linker, and the type of code being generated. The +impact on systems that support long absolute calls, and long pic +symbol-difference or pc-relative calls should be relatively small. +However, an indirect call is used on 32-bit ELF systems in pic code +and it is quite long. + +@item -munix=@var{unix-std} +@opindex march +Generate compiler predefines and select a startfile for the specified +UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} +and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} +is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX +11.11 and later. The default values are @samp{93} for HP-UX 10.00, +@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 +and later. + +@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. +@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} +and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. +@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, +@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and +@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. + +It is @emph{important} to note that this option changes the interfaces +for various library routines. It also affects the operational behavior +of the C library. Thus, @emph{extreme} care is needed in using this +option. + +Library code that is intended to operate with more than one UNIX +standard must test, set and restore the variable @var{__xpg4_extended_mask} +as appropriate. Most GNU software doesn't provide this capability. + +@item -nolibdld +@opindex nolibdld +Suppress the generation of link options to search libdld.sl when the +@option{-static} option is specified on HP-UX 10 and later. + +@item -static +@opindex static +The HP-UX implementation of setlocale in libc has a dependency on +libdld.sl. There isn't an archive version of libdld.sl. Thus, +when the @option{-static} option is specified, special link options +are needed to resolve this dependency. + +On HP-UX 10 and later, the GCC driver adds the necessary options to +link with libdld.sl when the @option{-static} option is specified. +This causes the resulting binary to be dynamic. On the 64-bit port, +the linkers generate dynamic binaries by default in any case. The +@option{-nolibdld} option can be used to prevent the GCC driver from +adding these link options. + +@item -threads +@opindex threads +Add support for multithreading with the @dfn{dce thread} library +under HP-UX@. This option sets flags for both the preprocessor and +linker. +@end table +@c APPLE LOCAL prune man page +@end ignore + +@node i386 and x86-64 Options +@subsection Intel 386 and AMD x86-64 Options +@cindex i386 Options +@cindex x86-64 Options +@cindex Intel 386 Options +@cindex AMD x86-64 Options + +These @samp{-m} options are defined for the i386 and x86-64 family of +computers: + +@table @gcctabopt +@item -mtune=@var{cpu-type} +@opindex mtune +Tune to @var{cpu-type} everything applicable about the generated code, except +for the ABI and the set of available instructions. The choices for +@var{cpu-type} are: +@table @emph +@item generic +Produce code optimized for the most common IA32/AMD64/EM64T processors. +If you know the CPU on which your code will run, then you should use +the corresponding @option{-mtune} option instead of +@option{-mtune=generic}. But, if you do not know exactly what CPU users +of your application will have, then you should use this option. + +As new processors are deployed in the marketplace, the behavior of this +option will change. Therefore, if you upgrade to a newer version of +GCC, the code generated option will change to reflect the processors +that were most common when that version of GCC was released. + +There is no @option{-march=generic} option because @option{-march} +indicates the instruction set the compiler can use, and there is no +generic instruction set applicable to all processors. In contrast, +@option{-mtune} indicates the processor (or, in this case, collection of +processors) for which the code is optimized. +@item native +This selects the CPU to tune for at compilation time by determining +the processor type of the compiling machine. Using @option{-mtune=native} +will produce code optimized for the local machine under the constraints +of the selected instruction set. Using @option{-march=native} will +enable all instruction subsets supported by the local machine (hence +the result might not run on different machines). +@item i386 +Original Intel's i386 CPU@. +@item i486 +Intel's i486 CPU@. (No scheduling is implemented for this chip.) +@item i586, pentium +Intel Pentium CPU with no MMX support. +@item pentium-mmx +Intel PentiumMMX CPU based on Pentium core with MMX instruction set support. +@item pentiumpro +Intel PentiumPro CPU@. +@item i686 +Same as @code{generic}, but when used as @code{march} option, PentiumPro +instruction set will be used, so the code will run on all i686 family chips. +@item pentium2 +Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support. +@item pentium3, pentium3m +Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set +support. +@item pentium-m +Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set +support. Used by Centrino notebooks. +@item pentium4, pentium4m +Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support. +@item prescott +Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction +set support. +@item nocona +Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE, +SSE2 and SSE3 instruction set support. +@c APPLE LOCAL begin mainline +@item core2 +Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 +instruction set support. +@c APPLE LOCAL end mainline +@item k6 +AMD K6 CPU with MMX instruction set support. +@item k6-2, k6-3 +Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support. +@item athlon, athlon-tbird +AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions +support. +@item athlon-4, athlon-xp, athlon-mp +Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE +instruction set support. +@item k8, opteron, athlon64, athlon-fx +AMD K8 core based CPUs with x86-64 instruction set support. (This supersets +MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.) +@item winchip-c6 +IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction +set support. +@item winchip2 +IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW! +instruction set support. +@item c3 +Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is +implemented for this chip.) +@item c3-2 +Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is +implemented for this chip.) +@end table + +While picking a specific @var{cpu-type} will schedule things appropriately +for that particular chip, the compiler will not generate any code that +does not run on the i386 without the @option{-march=@var{cpu-type}} option +being used. + +@item -march=@var{cpu-type} +@opindex march +Generate instructions for the machine type @var{cpu-type}. The choices +for @var{cpu-type} are the same as for @option{-mtune}. Moreover, +specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}. + +@item -mcpu=@var{cpu-type} +@opindex mcpu +A deprecated synonym for @option{-mtune}. + +@item -m386 +@itemx -m486 +@itemx -mpentium +@itemx -mpentiumpro +@opindex m386 +@opindex m486 +@opindex mpentium +@opindex mpentiumpro +These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486}, +@option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively. +These synonyms are deprecated. + +@item -mfpmath=@var{unit} +@opindex march +Generate floating point arithmetics for selected unit @var{unit}. The choices +for @var{unit} are: + +@table @samp +@item 387 +Use the standard 387 floating point coprocessor present majority of chips and +emulated otherwise. Code compiled with this option will run almost everywhere. +The temporary results are computed in 80bit precision instead of precision +specified by the type resulting in slightly different results compared to most +of other chips. See @option{-ffloat-store} for more detailed description. + +This is the default choice for i386 compiler. + +@item sse +Use scalar floating point instructions present in the SSE instruction set. +This instruction set is supported by Pentium3 and newer chips, in the AMD line +by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE +instruction set supports only single precision arithmetics, thus the double and +extended precision arithmetics is still done using 387. Later version, present +only in Pentium4 and the future AMD x86-64 chips supports double precision +arithmetics too. + +For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse} +or @option{-msse2} switches to enable SSE extensions and make this option +effective. For the x86-64 compiler, these extensions are enabled by default. + +The resulting code should be considerably faster in the majority of cases and avoid +the numerical instability problems of 387 code, but may break some existing +code that expects temporaries to be 80bit. + +This is the default choice for the x86-64 compiler. + +@item sse,387 +Attempt to utilize both instruction sets at once. This effectively double the +amount of available registers and on chips with separate execution units for +387 and SSE the execution resources too. Use this option with care, as it is +still experimental, because the GCC register allocator does not model separate +functional units well resulting in instable performance. +@end table + +@item -masm=@var{dialect} +@opindex masm=@var{dialect} +Output asm instructions using selected @var{dialect}. Supported +choices are @samp{intel} or @samp{att} (the default one). Darwin does +not support @samp{intel}. + +@item -mieee-fp +@itemx -mno-ieee-fp +@opindex mieee-fp +@opindex mno-ieee-fp +Control whether or not the compiler uses IEEE floating point +comparisons. These handle correctly the case where the result of a +comparison is unordered. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not part of GCC@. +Normally the facilities of the machine's usual C compiler are used, but +this can't be done directly in cross-compilation. You must make your +own arrangements to provide suitable library functions for +cross-compilation. + +On machines where a function returns floating point results in the 80387 +register stack, some floating point opcodes may be emitted even if +@option{-msoft-float} is used. + +@item -mno-fp-ret-in-387 +@opindex mno-fp-ret-in-387 +Do not use the FPU registers for return values of functions. + +The usual calling convention has functions return values of types +@code{float} and @code{double} in an FPU register, even if there +is no FPU@. The idea is that the operating system should emulate +an FPU@. + +The option @option{-mno-fp-ret-in-387} causes such values to be returned +in ordinary CPU registers instead. + +@item -mno-fancy-math-387 +@opindex mno-fancy-math-387 +Some 387 emulators do not support the @code{sin}, @code{cos} and +@code{sqrt} instructions for the 387. Specify this option to avoid +generating those instructions. This option is the default on FreeBSD, +OpenBSD and NetBSD@. This option is overridden when @option{-march} +indicates that the target cpu will always have an FPU and so the +instruction will not need emulation. As of revision 2.6.1, these +instructions are not generated unless you also use the +@option{-funsafe-math-optimizations} switch. + +@item -malign-double +@itemx -mno-align-double +@opindex malign-double +@opindex mno-align-double +Control whether GCC aligns @code{double}, @code{long double}, and +@code{long long} variables on a two word boundary or a one word +boundary. Aligning @code{double} variables on a two word boundary will +produce code that runs somewhat faster on a @samp{Pentium} at the +expense of more memory. + +On x86-64, @option{-malign-double} is enabled by default. + +@strong{Warning:} if you use the @option{-malign-double} switch, +structures containing the above types will be aligned differently than +the published application binary interface specifications for the 386 +and will not be binary compatible with structures in code compiled +without that switch. + +@item -m96bit-long-double +@itemx -m128bit-long-double +@opindex m96bit-long-double +@opindex m128bit-long-double +These switches control the size of @code{long double} type. The i386 +application binary interface specifies the size to be 96 bits, +so @option{-m96bit-long-double} is the default in 32 bit mode. + +Modern architectures (Pentium and newer) would prefer @code{long double} +to be aligned to an 8 or 16 byte boundary. In arrays or structures +conforming to the ABI, this would not be possible. So specifying a +@option{-m128bit-long-double} will align @code{long double} +to a 16 byte boundary by padding the @code{long double} with an additional +32 bit zero. + +In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as +its ABI specifies that @code{long double} is to be aligned on 16 byte boundary. + +Notice that neither of these options enable any extra precision over the x87 +standard of 80 bits for a @code{long double}. + +@strong{Warning:} if you override the default value for your target ABI, the +structures and arrays containing @code{long double} variables will change +their size as well as function calling convention for function taking +@code{long double} will be modified. Hence they will not be binary +compatible with arrays or structures in code compiled without that switch. + +@item -mmlarge-data-threshold=@var{number} +@opindex mlarge-data-threshold=@var{number} +When @option{-mcmodel=medium} is specified, the data greater than +@var{threshold} are placed in large data section. This value must be the +same across all object linked into the binary and defaults to 65535. + +@item -msvr3-shlib +@itemx -mno-svr3-shlib +@opindex msvr3-shlib +@opindex mno-svr3-shlib +Control whether GCC places uninitialized local variables into the +@code{bss} or @code{data} segments. @option{-msvr3-shlib} places them +into @code{bss}. These options are meaningful only on System V Release 3. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions that +take a fixed number of arguments return with the @code{ret} @var{num} +instruction, which pops their arguments while returning. This saves one +instruction in the caller since there is no need to pop the arguments +there. + +You can specify that an individual function is called with this calling +sequence with the function attribute @samp{stdcall}. You can also +override the @option{-mrtd} option by using the function attribute +@samp{cdecl}. @xref{Function Attributes}. + +@strong{Warning:} this calling convention is incompatible with the one +normally used on Unix, so you cannot use it if you need to call +libraries compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code will be generated for calls to those +functions. + +In addition, seriously incorrect code will result if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +@item -mregparm=@var{num} +@opindex mregparm +Control how many registers are used to pass integer arguments. By +default, no registers are used to pass arguments, and at most 3 +registers can be used. You can control this behavior for a specific +function by using the function attribute @samp{regparm}. +@xref{Function Attributes}. + +@strong{Warning:} if you use this switch, and +@var{num} is nonzero, then you must build all modules with the same +value, including any libraries. This includes the system libraries and +startup modules. + +@item -msseregparm +@opindex msseregparm +Use SSE register passing conventions for float and double arguments +and return values. You can control this behavior for a specific +function by using the function attribute @samp{sseregparm}. +@xref{Function Attributes}. + +@strong{Warning:} if you use this switch then you must build all +modules with the same value, including any libraries. This includes +the system libraries and startup modules. + +@item -mstackrealign +@opindex mstackrealign +Realign the stack at entry. On the Intel x86, the +@option{-mstackrealign} option will generate an alternate prologue and +epilogue that realigns the runtime stack. This supports mixing legacy +codes that keep a 4-byte aligned stack with modern codes that keep a +16-byte stack for SSE compatibility. The alternate prologue and +epilogue are slower and bigger than the regular ones, and the +alternate prologue requires an extra scratch register; this lowers the +number of registers available if used in conjunction with the +@code{regparm} attribute. The @option{-mstackrealign} option is +incompatible with the nested function prologue; this is considered a +hard error. See also the attribute @code{force_align_arg_pointer}, +applicable to individual functions. + +@item -mpreferred-stack-boundary=@var{num} +@opindex mpreferred-stack-boundary +Attempt to keep the stack boundary aligned to a 2 raised to @var{num} +byte boundary. If @option{-mpreferred-stack-boundary} is not specified, +the default is 4 (16 bytes or 128 bits). + +On Pentium and PentiumPro, @code{double} and @code{long double} values +should be aligned to an 8 byte boundary (see @option{-malign-double}) or +suffer significant run time performance penalties. On Pentium III, the +Streaming SIMD Extension (SSE) data type @code{__m128} may not work +properly if it is not 16 byte aligned. + +To ensure proper alignment of this values on the stack, the stack boundary +must be as aligned as that required by any value stored on the stack. +Further, every function must be generated such that it keeps the stack +aligned. Thus calling a function compiled with a higher preferred +stack boundary from a function compiled with a lower preferred stack +boundary will most likely misalign the stack. It is recommended that +libraries that use callbacks always use the default setting. + +This extra alignment does consume extra stack space, and generally +increases code size. Code that is sensitive to stack space usage, such +as embedded systems and operating system kernels, may want to reduce the +preferred alignment to @option{-mpreferred-stack-boundary=2}. + +@item -mmmx +@itemx -mno-mmx +@item -msse +@itemx -mno-sse +@item -msse2 +@itemx -mno-sse2 +@item -msse3 +@itemx -mno-sse3 +@c APPLE LOCAL begin mainline +@item -mssse3 +@itemx -mno-ssse3 +@c APPLE LOCAL end mainline +@c APPLE LOCAL begin 5612787 sse4 +@item -msse4.1 +@itemx -mno-sse4.1 +@item -msse4.2 +@itemx -mno-sse4.2 +@item -msse4 +@itemx -mno-sse4 +@item -msse4a +@item -mno-sse4a +@c APPLE LOCAL end 5612787 sse4 +@item -m3dnow +@itemx -mno-3dnow +@opindex mmmx +@opindex mno-mmx +@opindex msse +@opindex mno-sse +@opindex m3dnow +@opindex mno-3dnow +These switches enable or disable the use of instructions in the MMX, +@c APPLE LOCAL begin 5612787 sse4 +SSE, SSE2, SSE3, SSSE3, 3Dnow, SSE4.1, SSE4.2, and SSE4A extended +instruction sets. These extensions are +@c APPLE LOCAL end 5612787 sse4 +also available as built-in functions: see @ref{X86 Built-in Functions}, +for details of the functions enabled and disabled by these switches. + +To have SSE/SSE2 instructions generated automatically from floating-point +code (as opposed to 387 instructions), see @option{-mfpmath=sse}. + +These options will enable GCC to use these extended instructions in +generated code, even without @option{-mfpmath=sse}. Applications which +perform runtime CPU detection must compile separate files for each +supported architecture, using the appropriate flags. In particular, +the file containing the CPU detection code should be compiled without +these options. + +@item -mpush-args +@itemx -mno-push-args +@opindex mpush-args +@opindex mno-push-args +Use PUSH operations to store outgoing parameters. This method is shorter +and usually equally fast as method using SUB/MOV operations and is enabled +by default. In some cases disabling it may improve performance because of +improved scheduling and reduced dependencies. + +@item -maccumulate-outgoing-args +@opindex maccumulate-outgoing-args +If enabled, the maximum amount of space required for outgoing arguments will be +computed in the function prologue. This is faster on most modern CPUs +because of reduced dependencies, improved scheduling and reduced stack usage +when preferred stack boundary is not equal to 2. The drawback is a notable +increase in code size. This switch implies @option{-mno-push-args}. + +@item -mthreads +@opindex mthreads +Support thread-safe exception handling on @samp{Mingw32}. Code that relies +on thread-safe exception handling must compile and link all code with the +@option{-mthreads} option. When compiling, @option{-mthreads} defines +@option{-D_MT}; when linking, it links in a special thread helper library +@option{-lmingwthrd} which cleans up per thread exception handling data. + +@item -mno-align-stringops +@opindex mno-align-stringops +Do not align destination of inlined string operations. This switch reduces +code size and improves performance in case the destination is already aligned, +but GCC doesn't know about it. + +@item -minline-all-stringops +@opindex minline-all-stringops +By default GCC inlines string operations only when destination is known to be +aligned at least to 4 byte boundary. This enables more inlining, increase code +size, but may improve performance of code that depends on fast memcpy, strlen +and memset for short lengths. + +@item -momit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +Don't keep the frame pointer in a register for leaf functions. This +avoids the instructions to save, set up and restore frame pointers and +makes an extra register available in leaf functions. The option +@option{-fomit-frame-pointer} removes the frame pointer for all functions +which might make debugging harder. + +@item -mtls-direct-seg-refs +@itemx -mno-tls-direct-seg-refs +@opindex mtls-direct-seg-refs +Controls whether TLS variables may be accessed with offsets from the +TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), +or whether the thread base pointer must be added. Whether or not this +is legal depends on the operating system, and whether it maps the +segment to cover the entire TLS area. + +For systems that use GNU libc, the default is on. +@end table + +These @samp{-m} switches are supported in addition to the above +on AMD x86-64 processors in 64-bit environments. + +@table @gcctabopt +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits and +generates code that runs on any i386 system. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits and generates code for AMD's x86-64 architecture. For +darwin only the -m64 option turns off the @option{-fno-pic} and +@option{-mdynamic-no-pic} options. + +@item -mno-red-zone +@opindex no-red-zone +Do not use a so called red zone for x86-64 code. The red zone is mandated +by the x86-64 ABI, it is a 128-byte area beyond the location of the +stack pointer that will not be modified by signal or interrupt handlers +and therefore can be used for temporary data without adjusting the stack +pointer. The flag @option{-mno-red-zone} disables this red zone. + +@item -mcmodel=small +@opindex mcmodel=small +Generate code for the small code model: the program and its symbols must +be linked in the lower 2 GB of the address space. Pointers are 64 bits. +Programs can be statically or dynamically linked. This is the default +code model. + +@item -mcmodel=kernel +@opindex mcmodel=kernel +Generate code for the kernel code model. The kernel runs in the +negative 2 GB of the address space. +This model has to be used for Linux kernel code. + +@item -mcmodel=medium +@opindex mcmodel=medium +Generate code for the medium model: The program is linked in the lower 2 +GB of the address space but symbols can be located anywhere in the +address space. Programs can be statically or dynamically linked, but +building of shared libraries are not supported with the medium model. + +@item -mcmodel=large +@opindex mcmodel=large +Generate code for the large model: This model makes no assumptions +about addresses and sizes of sections. Currently GCC does not implement +this model. + +@c APPLE LOCAL begin 5946347 ms_struct support +@item -mms-bitfields +@opindex mms-bitfields +Set the default structure layout to be compatible with the Microsoft +compiler standard. This is equivalent to adding an @code{ms_struct} +attribute to each structure and union tag definition. The default is +@option{mno-ms-bitfields}. +@c APPLE LOCAL end 5946347 ms_struct support + +@end table + +@c APPLE LOCAL prune man page +@ignore +@node IA-64 Options +@subsection IA-64 Options +@cindex IA-64 Options + +These are the @samp{-m} options defined for the Intel IA-64 architecture. + +@table @gcctabopt +@item -mbig-endian +@opindex mbig-endian +Generate code for a big endian target. This is the default for HP-UX@. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little endian target. This is the default for AIX5 +and GNU/Linux. + +@item -mgnu-as +@itemx -mno-gnu-as +@opindex mgnu-as +@opindex mno-gnu-as +Generate (or don't) code for the GNU assembler. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-as} +@c is used. + +@item -mgnu-ld +@itemx -mno-gnu-ld +@opindex mgnu-ld +@opindex mno-gnu-ld +Generate (or don't) code for the GNU linker. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-ld} +@c is used. + +@item -mno-pic +@opindex mno-pic +Generate code that does not use a global pointer register. The result +is not position independent code, and violates the IA-64 ABI@. + +@item -mvolatile-asm-stop +@itemx -mno-volatile-asm-stop +@opindex mvolatile-asm-stop +@opindex mno-volatile-asm-stop +Generate (or don't) a stop bit immediately before and after volatile asm +statements. + +@item -mregister-names +@itemx -mno-register-names +@opindex mregister-names +@opindex mno-register-names +Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for +the stacked registers. This may make assembler output more readable. + +@item -mno-sdata +@itemx -msdata +@opindex mno-sdata +@opindex msdata +Disable (or enable) optimizations that use the small data section. This may +be useful for working around optimizer bugs. + +@item -mconstant-gp +@opindex mconstant-gp +Generate code that uses a single constant global pointer value. This is +useful when compiling kernel code. + +@item -mauto-pic +@opindex mauto-pic +Generate code that is self-relocatable. This implies @option{-mconstant-gp}. +This is useful when compiling firmware code. + +@item -minline-float-divide-min-latency +@opindex minline-float-divide-min-latency +Generate code for inline divides of floating point values +using the minimum latency algorithm. + +@item -minline-float-divide-max-throughput +@opindex minline-float-divide-max-throughput +Generate code for inline divides of floating point values +using the maximum throughput algorithm. + +@item -minline-int-divide-min-latency +@opindex minline-int-divide-min-latency +Generate code for inline divides of integer values +using the minimum latency algorithm. + +@item -minline-int-divide-max-throughput +@opindex minline-int-divide-max-throughput +Generate code for inline divides of integer values +using the maximum throughput algorithm. + +@item -minline-sqrt-min-latency +@opindex minline-sqrt-min-latency +Generate code for inline square roots +using the minimum latency algorithm. + +@item -minline-sqrt-max-throughput +@opindex minline-sqrt-max-throughput +Generate code for inline square roots +using the maximum throughput algorithm. + +@item -mno-dwarf2-asm +@itemx -mdwarf2-asm +@opindex mno-dwarf2-asm +@opindex mdwarf2-asm +Don't (or do) generate assembler code for the DWARF2 line number debugging +info. This may be useful when not using the GNU assembler. + +@item -mearly-stop-bits +@itemx -mno-early-stop-bits +@opindex mearly-stop-bits +@opindex mno-early-stop-bits +Allow stop bits to be placed earlier than immediately preceding the +instruction that triggered the stop bit. This can improve instruction +scheduling, but does not always do so. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator can not use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. + +@item -mtls-size=@var{tls-size} +@opindex mtls-size +Specify bit size of immediate TLS offsets. Valid values are 14, 22, and +64. + +@item -mtune=@var{cpu-type} +@opindex mtune +Tune the instruction scheduling for a particular CPU, Valid values are +itanium, itanium1, merced, itanium2, and mckinley. + +@item -mt +@itemx -pthread +@opindex mt +@opindex pthread +Add support for multithreading using the POSIX threads library. This +option sets flags for both the preprocessor and linker. It does +not affect the thread safety of object code produced by the compiler or +that of libraries supplied with it. These are HP-UX specific flags. + +@item -milp32 +@itemx -mlp64 +@opindex milp32 +@opindex mlp64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits. These are HP-UX specific flags. + +@item -mno-sched-br-data-spec +@itemx -msched-br-data-spec +@opindex mno-sched-br-data-spec +@opindex msched-br-data-spec +(Dis/En)able data speculative scheduling before reload. +This will result in generation of the ld.a instructions and +the corresponding check instructions (ld.c / chk.a). +The default is 'disable'. + +@item -msched-ar-data-spec +@itemx -mno-sched-ar-data-spec +@opindex msched-ar-data-spec +@opindex mno-sched-ar-data-spec +(En/Dis)able data speculative scheduling after reload. +This will result in generation of the ld.a instructions and +the corresponding check instructions (ld.c / chk.a). +The default is 'enable'. + +@item -mno-sched-control-spec +@itemx -msched-control-spec +@opindex mno-sched-control-spec +@opindex msched-control-spec +(Dis/En)able control speculative scheduling. This feature is +available only during region scheduling (i.e. before reload). +This will result in generation of the ld.s instructions and +the corresponding check instructions chk.s . +The default is 'disable'. + +@item -msched-br-in-data-spec +@itemx -mno-sched-br-in-data-spec +@opindex msched-br-in-data-spec +@opindex mno-sched-br-in-data-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the data speculative loads before reload. +This is effective only with @option{-msched-br-data-spec} enabled. +The default is 'enable'. + +@item -msched-ar-in-data-spec +@itemx -mno-sched-ar-in-data-spec +@opindex msched-ar-in-data-spec +@opindex mno-sched-ar-in-data-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the data speculative loads after reload. +This is effective only with @option{-msched-ar-data-spec} enabled. +The default is 'enable'. + +@item -msched-in-control-spec +@itemx -mno-sched-in-control-spec +@opindex msched-in-control-spec +@opindex mno-sched-in-control-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the control speculative loads. +This is effective only with @option{-msched-control-spec} enabled. +The default is 'enable'. + +@item -msched-ldc +@itemx -mno-sched-ldc +@opindex msched-ldc +@opindex mno-sched-ldc +(En/Dis)able use of simple data speculation checks ld.c . +If disabled, only chk.a instructions will be emitted to check +data speculative loads. +The default is 'enable'. + +@item -mno-sched-control-ldc +@itemx -msched-control-ldc +@opindex mno-sched-control-ldc +@opindex msched-control-ldc +(Dis/En)able use of ld.c instructions to check control speculative loads. +If enabled, in case of control speculative load with no speculatively +scheduled dependent instructions this load will be emitted as ld.sa and +ld.c will be used to check it. +The default is 'disable'. + +@item -mno-sched-spec-verbose +@itemx -msched-spec-verbose +@opindex mno-sched-spec-verbose +@opindex msched-spec-verbose +(Dis/En)able printing of the information about speculative motions. + +@item -mno-sched-prefer-non-data-spec-insns +@itemx -msched-prefer-non-data-spec-insns +@opindex mno-sched-prefer-non-data-spec-insns +@opindex msched-prefer-non-data-spec-insns +If enabled, data speculative instructions will be chosen for schedule +only if there are no other choices at the moment. This will make +the use of the data speculation much more conservative. +The default is 'disable'. + +@item -mno-sched-prefer-non-control-spec-insns +@itemx -msched-prefer-non-control-spec-insns +@opindex mno-sched-prefer-non-control-spec-insns +@opindex msched-prefer-non-control-spec-insns +If enabled, control speculative instructions will be chosen for schedule +only if there are no other choices at the moment. This will make +the use of the control speculation much more conservative. +The default is 'disable'. + +@item -mno-sched-count-spec-in-critical-path +@itemx -msched-count-spec-in-critical-path +@opindex mno-sched-count-spec-in-critical-path +@opindex msched-count-spec-in-critical-path +If enabled, speculative dependencies will be considered during +computation of the instructions priorities. This will make the use of the +speculation a bit more conservative. +The default is 'disable'. + +@end table + +@node M32C Options +@subsection M32C Options +@cindex M32C options + +@table @gcctabopt +@item -mcpu=@var{name} +@opindex mcpu= +Select the CPU for which code is generated. @var{name} may be one of +@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to +/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for +the M32C/80 series. + +@item -msim +@opindex msim +Specifies that the program will be run on the simulator. This causes +an alternate runtime library to be linked in which supports, for +example, file I/O. You must not use this option when generating +programs that will run on real hardware; you must provide your own +runtime library for whatever I/O functions are needed. + +@item -memregs=@var{number} +@opindex memregs= +Specifies the number of memory-based pseudo-registers GCC will use +during code generation. These pseudo-registers will be used like real +registers, so there is a tradeoff between GCC's ability to fit the +code into available registers, and the performance penalty of using +memory instead of registers. Note that all modules in a program must +be compiled with the same value for this option. Because of that, you +must not use this option with the default runtime libraries gcc +builds. + +@end table + +@node M32R/D Options +@subsection M32R/D Options +@cindex M32R/D options + +These @option{-m} options are defined for Renesas M32R/D architectures: + +@table @gcctabopt +@item -m32r2 +@opindex m32r2 +Generate code for the M32R/2@. + +@item -m32rx +@opindex m32rx +Generate code for the M32R/X@. + +@item -m32r +@opindex m32r +Generate code for the M32R@. This is the default. + +@item -mmodel=small +@opindex mmodel=small +Assume all objects live in the lower 16MB of memory (so that their addresses +can be loaded with the @code{ld24} instruction), and assume all subroutines +are reachable with the @code{bl} instruction. +This is the default. + +The addressability of a particular object can be set with the +@code{model} attribute. + +@item -mmodel=medium +@opindex mmodel=medium +Assume objects may be anywhere in the 32-bit address space (the compiler +will generate @code{seth/add3} instructions to load their addresses), and +assume all subroutines are reachable with the @code{bl} instruction. + +@item -mmodel=large +@opindex mmodel=large +Assume objects may be anywhere in the 32-bit address space (the compiler +will generate @code{seth/add3} instructions to load their addresses), and +assume subroutines may not be reachable with the @code{bl} instruction +(the compiler will generate the much slower @code{seth/add3/jl} +instruction sequence). + +@item -msdata=none +@opindex msdata=none +Disable use of the small data area. Variables will be put into +one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the +@code{section} attribute has been specified). +This is the default. + +The small data area consists of sections @samp{.sdata} and @samp{.sbss}. +Objects may be explicitly put in the small data area with the +@code{section} attribute using one of these sections. + +@item -msdata=sdata +@opindex msdata=sdata +Put small global and static data in the small data area, but do not +generate special code to reference them. + +@item -msdata=use +@opindex msdata=use +Put small global and static data in the small data area, and generate +special instructions to reference them. + +@item -G @var{num} +@opindex G +@cindex smaller data references +Put global and static objects less than or equal to @var{num} bytes +into the small data or bss sections instead of the normal data or bss +sections. The default value of @var{num} is 8. +The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} +for this option to have any effect. + +All modules should be compiled with the same @option{-G @var{num}} value. +Compiling with different values of @var{num} may or may not work; if it +doesn't the linker will give an error message---incorrect code will not be +generated. + +@item -mdebug +@opindex mdebug +Makes the M32R specific code in the compiler display some statistics +that might help in debugging programs. + +@item -malign-loops +@opindex malign-loops +Align all loops to a 32-byte boundary. + +@item -mno-align-loops +@opindex mno-align-loops +Do not enforce a 32-byte alignment for loops. This is the default. + +@item -missue-rate=@var{number} +@opindex missue-rate=@var{number} +Issue @var{number} instructions per cycle. @var{number} can only be 1 +or 2. + +@item -mbranch-cost=@var{number} +@opindex mbranch-cost=@var{number} +@var{number} can only be 1 or 2. If it is 1 then branches will be +preferred over conditional code, if it is 2, then the opposite will +apply. + +@item -mflush-trap=@var{number} +@opindex mflush-trap=@var{number} +Specifies the trap number to use to flush the cache. The default is +12. Valid numbers are between 0 and 15 inclusive. + +@item -mno-flush-trap +@opindex mno-flush-trap +Specifies that the cache cannot be flushed by using a trap. + +@item -mflush-func=@var{name} +@opindex mflush-func=@var{name} +Specifies the name of the operating system function to call to flush +the cache. The default is @emph{_flush_cache}, but a function call +will only be used if a trap is not available. + +@item -mno-flush-func +@opindex mno-flush-func +Indicates that there is no OS function for flushing the cache. + +@end table + +@node M680x0 Options +@subsection M680x0 Options +@cindex M680x0 options + +These are the @samp{-m} options defined for the 68000 series. The default +values for these options depends on which style of 68000 was selected when +the compiler was configured; the defaults for the most common choices are +given below. + +@table @gcctabopt +@item -m68000 +@itemx -mc68000 +@opindex m68000 +@opindex mc68000 +Generate output for a 68000. This is the default +when the compiler is configured for 68000-based systems. + +Use this option for microcontrollers with a 68000 or EC000 core, +including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. + +@item -m68020 +@itemx -mc68020 +@opindex m68020 +@opindex mc68020 +Generate output for a 68020. This is the default +when the compiler is configured for 68020-based systems. + +@item -m68881 +@opindex m68881 +Generate output containing 68881 instructions for floating point. +This is the default for most 68020 systems unless @option{--nfp} was +specified when the compiler was configured. + +@item -m68030 +@opindex m68030 +Generate output for a 68030. This is the default when the compiler is +configured for 68030-based systems. + +@item -m68040 +@opindex m68040 +Generate output for a 68040. This is the default when the compiler is +configured for 68040-based systems. + +This option inhibits the use of 68881/68882 instructions that have to be +emulated by software on the 68040. Use this option if your 68040 does not +have code to emulate those instructions. + +@item -m68060 +@opindex m68060 +Generate output for a 68060. This is the default when the compiler is +configured for 68060-based systems. + +This option inhibits the use of 68020 and 68881/68882 instructions that +have to be emulated by software on the 68060. Use this option if your 68060 +does not have code to emulate those instructions. + +@item -mcpu32 +@opindex mcpu32 +Generate output for a CPU32. This is the default +when the compiler is configured for CPU32-based systems. + +Use this option for microcontrollers with a +CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, +68336, 68340, 68341, 68349 and 68360. + +@item -m5200 +@opindex m5200 +Generate output for a 520X ``coldfire'' family cpu. This is the default +when the compiler is configured for 520X-based systems. + +Use this option for microcontroller with a 5200 core, including +the MCF5202, MCF5203, MCF5204 and MCF5202. + +@item -mcfv4e +@opindex mcfv4e +Generate output for a ColdFire V4e family cpu (e.g.@: 547x/548x). +This includes use of hardware floating point instructions. + +@item -m68020-40 +@opindex m68020-40 +Generate output for a 68040, without using any of the new instructions. +This results in code which can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68040. + +@item -m68020-60 +@opindex m68020-60 +Generate output for a 68060, without using any of the new instructions. +This results in code which can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68060. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all m68k +targets. Normally the facilities of the machine's usual C compiler are +used, but this can't be done directly in cross-compilation. You must +make your own arrangements to provide suitable library functions for +cross-compilation. The embedded targets @samp{m68k-*-aout} and +@samp{m68k-*-coff} do provide software floating point support. + +@item -mshort +@opindex mshort +Consider type @code{int} to be 16 bits wide, like @code{short int}. +Additionally, parameters passed on the stack are also aligned to a +16-bit boundary even on targets whose API mandates promotion to 32-bit. + +@item -mnobitfield +@opindex mnobitfield +Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} +and @option{-m5200} options imply @w{@option{-mnobitfield}}. + +@item -mbitfield +@opindex mbitfield +Do use the bit-field instructions. The @option{-m68020} option implies +@option{-mbitfield}. This is the default if you use a configuration +designed for a 68020. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions +that take a fixed number of arguments return with the @code{rtd} +instruction, which pops their arguments while returning. This +saves one instruction in the caller since there is no need to pop +the arguments there. + +This calling convention is incompatible with the one normally +used on Unix, so you cannot use it if you need to call libraries +compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code will be generated for calls to those +functions. + +In addition, seriously incorrect code will result if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +The @code{rtd} instruction is supported by the 68010, 68020, 68030, +68040, 68060 and CPU32 processors, but not by the 68000 or 5200. + +@item -malign-int +@itemx -mno-align-int +@opindex malign-int +@opindex mno-align-int +Control whether GCC aligns @code{int}, @code{long}, @code{long long}, +@code{float}, @code{double}, and @code{long double} variables on a 32-bit +boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). +Aligning variables on 32-bit boundaries produces code that runs somewhat +faster on processors with 32-bit busses at the expense of more memory. + +@strong{Warning:} if you use the @option{-malign-int} switch, GCC will +align structures containing the above types differently than +most published application binary interface specifications for the m68k. + +@item -mpcrel +@opindex mpcrel +Use the pc-relative addressing mode of the 68000 directly, instead of +using a global offset table. At present, this option implies @option{-fpic}, +allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is +not presently supported with @option{-mpcrel}, though this could be supported for +68020 and higher processors. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +Do not (do) assume that unaligned memory references will be handled by +the system. + +@item -msep-data +Generate code that allows the data segment to be located in a different +area of memory from the text segment. This allows for execute in place in +an environment without virtual memory management. This option implies +@option{-fPIC}. + +@item -mno-sep-data +Generate code that assumes that the data segment follows the text segment. +This is the default. + +@item -mid-shared-library +Generate code that supports shared libraries via the library ID method. +This allows for execute in place and shared libraries in an environment +without virtual memory management. This option implies @option{-fPIC}. + +@item -mno-id-shared-library +Generate code that doesn't assume ID based shared libraries are being used. +This is the default. + +@item -mshared-library-id=n +Specified the identification number of the ID based shared library being +compiled. Specifying a value of 0 will generate more compact code, specifying +other values will force the allocation of that number to the current +library but is no more space or time efficient than omitting this option. + +@end table + +@node M68hc1x Options +@subsection M68hc1x Options +@cindex M68hc1x options + +These are the @samp{-m} options defined for the 68hc11 and 68hc12 +microcontrollers. The default values for these options depends on +which style of microcontroller was selected when the compiler was configured; +the defaults for the most common choices are given below. + +@table @gcctabopt +@item -m6811 +@itemx -m68hc11 +@opindex m6811 +@opindex m68hc11 +Generate output for a 68HC11. This is the default +when the compiler is configured for 68HC11-based systems. + +@item -m6812 +@itemx -m68hc12 +@opindex m6812 +@opindex m68hc12 +Generate output for a 68HC12. This is the default +when the compiler is configured for 68HC12-based systems. + +@item -m68S12 +@itemx -m68hcs12 +@opindex m68S12 +@opindex m68hcs12 +Generate output for a 68HCS12. + +@item -mauto-incdec +@opindex mauto-incdec +Enable the use of 68HC12 pre and post auto-increment and auto-decrement +addressing modes. + +@item -minmax +@itemx -nominmax +@opindex minmax +@opindex mnominmax +Enable the use of 68HC12 min and max instructions. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Treat all calls as being far away (near). If calls are assumed to be +far away, the compiler will use the @code{call} instruction to +call a function and the @code{rtc} instruction for returning. + +@item -mshort +@opindex mshort +Consider type @code{int} to be 16 bits wide, like @code{short int}. + +@item -msoft-reg-count=@var{count} +@opindex msoft-reg-count +Specify the number of pseudo-soft registers which are used for the +code generation. The maximum number is 32. Using more pseudo-soft +register may or may not result in better code depending on the program. +The default is 4 for 68HC11 and 2 for 68HC12. + +@end table + +@node MCore Options +@subsection MCore Options +@cindex MCore options + +These are the @samp{-m} options defined for the Motorola M*Core +processors. + +@table @gcctabopt + +@item -mhardlit +@itemx -mno-hardlit +@opindex mhardlit +@opindex mno-hardlit +Inline constants into the code stream if it can be done in two +instructions or less. + +@item -mdiv +@itemx -mno-div +@opindex mdiv +@opindex mno-div +Use the divide instruction. (Enabled by default). + +@item -mrelax-immediate +@itemx -mno-relax-immediate +@opindex mrelax-immediate +@opindex mno-relax-immediate +Allow arbitrary sized immediates in bit operations. + +@item -mwide-bitfields +@itemx -mno-wide-bitfields +@opindex mwide-bitfields +@opindex mno-wide-bitfields +Always treat bit-fields as int-sized. + +@item -m4byte-functions +@itemx -mno-4byte-functions +@opindex m4byte-functions +@opindex mno-4byte-functions +Force all functions to be aligned to a four byte boundary. + +@item -mcallgraph-data +@itemx -mno-callgraph-data +@opindex mcallgraph-data +@opindex mno-callgraph-data +Emit callgraph information. + +@item -mslow-bytes +@itemx -mno-slow-bytes +@opindex mslow-bytes +@opindex mno-slow-bytes +Prefer word access when reading byte quantities. + +@item -mlittle-endian +@itemx -mbig-endian +@opindex mlittle-endian +@opindex mbig-endian +Generate code for a little endian target. + +@item -m210 +@itemx -m340 +@opindex m210 +@opindex m340 +Generate code for the 210 processor. +@end table + +@node MIPS Options +@subsection MIPS Options +@cindex MIPS options + +@table @gcctabopt + +@item -EB +@opindex EB +Generate big-endian code. + +@item -EL +@opindex EL +Generate little-endian code. This is the default for @samp{mips*el-*-*} +configurations. + +@item -march=@var{arch} +@opindex march +Generate code that will run on @var{arch}, which can be the name of a +generic MIPS ISA, or the name of a particular processor. +The ISA names are: +@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, +@samp{mips32}, @samp{mips32r2}, and @samp{mips64}. +The processor names are: +@samp{4kc}, @samp{4km}, @samp{4kp}, +@samp{5kc}, @samp{5kf}, +@samp{20kc}, +@samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx}, +@samp{m4k}, +@samp{orion}, +@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, +@samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, +@samp{rm7000}, @samp{rm9000}, +@samp{sb1}, +@samp{sr71000}, +@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, +@samp{vr5000}, @samp{vr5400} and @samp{vr5500}. +The special value @samp{from-abi} selects the +most compatible architecture for the selected ABI (that is, +@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. + +In processor names, a final @samp{000} can be abbreviated as @samp{k} +(for example, @samp{-march=r2k}). Prefixes are optional, and +@samp{vr} may be written @samp{r}. + +GCC defines two macros based on the value of this option. The first +is @samp{_MIPS_ARCH}, which gives the name of target architecture, as +a string. The second has the form @samp{_MIPS_ARCH_@var{foo}}, +where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@. +For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH} +to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}. + +Note that the @samp{_MIPS_ARCH} macro uses the processor names given +above. In other words, it will have the full prefix and will not +abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, +the macro names the resolved architecture (either @samp{"mips1"} or +@samp{"mips3"}). It names the default architecture when no +@option{-march} option is given. + +@item -mtune=@var{arch} +@opindex mtune +Optimize for @var{arch}. Among other things, this option controls +the way instructions are scheduled, and the perceived cost of arithmetic +operations. The list of @var{arch} values is the same as for +@option{-march}. + +When this option is not used, GCC will optimize for the processor +specified by @option{-march}. By using @option{-march} and +@option{-mtune} together, it is possible to generate code that will +run on a family of processors, but optimize the code for one +particular member of that family. + +@samp{-mtune} defines the macros @samp{_MIPS_TUNE} and +@samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the +@samp{-march} ones described above. + +@item -mips1 +@opindex mips1 +Equivalent to @samp{-march=mips1}. + +@item -mips2 +@opindex mips2 +Equivalent to @samp{-march=mips2}. + +@item -mips3 +@opindex mips3 +Equivalent to @samp{-march=mips3}. + +@item -mips4 +@opindex mips4 +Equivalent to @samp{-march=mips4}. + +@item -mips32 +@opindex mips32 +Equivalent to @samp{-march=mips32}. + +@item -mips32r2 +@opindex mips32r2 +Equivalent to @samp{-march=mips32r2}. + +@item -mips64 +@opindex mips64 +Equivalent to @samp{-march=mips64}. + +@item -mips16 +@itemx -mno-mips16 +@opindex mips16 +@opindex mno-mips16 +Generate (do not generate) MIPS16 code. If GCC is targetting a +MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@. + +@item -mabi=32 +@itemx -mabi=o64 +@itemx -mabi=n32 +@itemx -mabi=64 +@itemx -mabi=eabi +@opindex mabi=32 +@opindex mabi=o64 +@opindex mabi=n32 +@opindex mabi=64 +@opindex mabi=eabi +Generate code for the given ABI@. + +Note that the EABI has a 32-bit and a 64-bit variant. GCC normally +generates 64-bit code when you select a 64-bit architecture, but you +can use @option{-mgp32} to get 32-bit code instead. + +For information about the O64 ABI, see +@w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}. + +@item -mabicalls +@itemx -mno-abicalls +@opindex mabicalls +@opindex mno-abicalls +Generate (do not generate) code that is suitable for SVR4-style +dynamic objects. @option{-mabicalls} is the default for SVR4-based +systems. + +@item -mshared +@itemx -mno-shared +Generate (do not generate) code that is fully position-independent, +and that can therefore be linked into shared libraries. This option +only affects @option{-mabicalls}. + +All @option{-mabicalls} code has traditionally been position-independent, +regardless of options like @option{-fPIC} and @option{-fpic}. However, +as an extension, the GNU toolchain allows executables to use absolute +accesses for locally-binding symbols. It can also use shorter GP +initialization sequences and generate direct calls to locally-defined +functions. This mode is selected by @option{-mno-shared}. + +@option{-mno-shared} depends on binutils 2.16 or higher and generates +objects that can only be linked by the GNU linker. However, the option +does not affect the ABI of the final executable; it only affects the ABI +of relocatable objects. Using @option{-mno-shared} will generally make +executables both smaller and quicker. + +@option{-mshared} is the default. + +@item -mxgot +@itemx -mno-xgot +@opindex mxgot +@opindex mno-xgot +Lift (do not lift) the usual restrictions on the size of the global +offset table. + +GCC normally uses a single instruction to load values from the GOT@. +While this is relatively efficient, it will only work if the GOT +is smaller than about 64k. Anything larger will cause the linker +to report an error such as: + +@cindex relocation truncated to fit (MIPS) +@smallexample +relocation truncated to fit: R_MIPS_GOT16 foobar +@end smallexample + +If this happens, you should recompile your code with @option{-mxgot}. +It should then work with very large GOTs, although it will also be +less efficient, since it will take three instructions to fetch the +value of a global symbol. + +Note that some linkers can create multiple GOTs. If you have such a +linker, you should only need to use @option{-mxgot} when a single object +file accesses more than 64k's worth of GOT entries. Very few do. + +These options have no effect unless GCC is generating position +independent code. + +@item -mgp32 +@opindex mgp32 +Assume that general-purpose registers are 32 bits wide. + +@item -mgp64 +@opindex mgp64 +Assume that general-purpose registers are 64 bits wide. + +@item -mfp32 +@opindex mfp32 +Assume that floating-point registers are 32 bits wide. + +@item -mfp64 +@opindex mfp64 +Assume that floating-point registers are 64 bits wide. + +@item -mhard-float +@opindex mhard-float +Use floating-point coprocessor instructions. + +@item -msoft-float +@opindex msoft-float +Do not use floating-point coprocessor instructions. Implement +floating-point calculations using library calls instead. + +@item -msingle-float +@opindex msingle-float +Assume that the floating-point coprocessor only supports single-precision +operations. + +@itemx -mdouble-float +@opindex mdouble-float +Assume that the floating-point coprocessor supports double-precision +operations. This is the default. + +@itemx -mdsp +@itemx -mno-dsp +@opindex mdsp +@opindex mno-dsp +Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}. + +@itemx -mpaired-single +@itemx -mno-paired-single +@opindex mpaired-single +@opindex mno-paired-single +Use (do not use) paired-single floating-point instructions. +@xref{MIPS Paired-Single Support}. This option can only be used +when generating 64-bit code and requires hardware floating-point +support to be enabled. + +@itemx -mips3d +@itemx -mno-mips3d +@opindex mips3d +@opindex mno-mips3d +Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. +The option @option{-mips3d} implies @option{-mpaired-single}. + +@item -mlong64 +@opindex mlong64 +Force @code{long} types to be 64 bits wide. See @option{-mlong32} for +an explanation of the default and the way that the pointer size is +determined. + +@item -mlong32 +@opindex mlong32 +Force @code{long}, @code{int}, and pointer types to be 32 bits wide. + +The default size of @code{int}s, @code{long}s and pointers depends on +the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI +uses 64-bit @code{long}s, as does the 64-bit EABI; the others use +32-bit @code{long}s. Pointers are the same size as @code{long}s, +or the same size as integer registers, whichever is smaller. + +@item -msym32 +@itemx -mno-sym32 +@opindex msym32 +@opindex mno-sym32 +Assume (do not assume) that all symbols have 32-bit values, regardless +of the selected ABI@. This option is useful in combination with +@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC +to generate shorter and faster references to symbolic addresses. + +@item -G @var{num} +@opindex G +@cindex smaller data references (MIPS) +@cindex gp-relative references (MIPS) +Put global and static items less than or equal to @var{num} bytes into +the small data or bss section instead of the normal data or bss section. +This allows the data to be accessed using a single instruction. + +All modules should be compiled with the same @option{-G @var{num}} +value. + +@item -membedded-data +@itemx -mno-embedded-data +@opindex membedded-data +@opindex mno-embedded-data +Allocate variables to the read-only data section first if possible, then +next in the small data section if possible, otherwise in data. This gives +slightly slower code than the default, but reduces the amount of RAM required +when executing, and thus may be preferred for some embedded systems. + +@item -muninit-const-in-rodata +@itemx -mno-uninit-const-in-rodata +@opindex muninit-const-in-rodata +@opindex mno-uninit-const-in-rodata +Put uninitialized @code{const} variables in the read-only data section. +This option is only meaningful in conjunction with @option{-membedded-data}. + +@item -msplit-addresses +@itemx -mno-split-addresses +@opindex msplit-addresses +@opindex mno-split-addresses +Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler +relocation operators. This option has been superseded by +@option{-mexplicit-relocs} but is retained for backwards compatibility. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Use (do not use) assembler relocation operators when dealing with symbolic +addresses. The alternative, selected by @option{-mno-explicit-relocs}, +is to use assembler macros instead. + +@option{-mexplicit-relocs} is the default if GCC was configured +to use an assembler that supports relocation operators. + +@item -mcheck-zero-division +@itemx -mno-check-zero-division +@opindex mcheck-zero-division +@opindex mno-check-zero-division +Trap (do not trap) on integer division by zero. The default is +@option{-mcheck-zero-division}. + +@item -mdivide-traps +@itemx -mdivide-breaks +@opindex mdivide-traps +@opindex mdivide-breaks +MIPS systems check for division by zero by generating either a +conditional trap or a break instruction. Using traps results in +smaller code, but is only supported on MIPS II and later. Also, some +versions of the Linux kernel have a bug that prevents trap from +generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to +allow conditional traps on architectures that support them and +@option{-mdivide-breaks} to force the use of breaks. + +The default is usually @option{-mdivide-traps}, but this can be +overridden at configure time using @option{--with-divide=breaks}. +Divide-by-zero checks can be completely disabled using +@option{-mno-check-zero-division}. + +@item -mmemcpy +@itemx -mno-memcpy +@opindex mmemcpy +@opindex mno-memcpy +Force (do not force) the use of @code{memcpy()} for non-trivial block +moves. The default is @option{-mno-memcpy}, which allows GCC to inline +most constant-sized copies. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Disable (do not disable) use of the @code{jal} instruction. Calling +functions using @code{jal} is more efficient but requires the caller +and callee to be in the same 256 megabyte segment. + +This option has no effect on abicalls code. The default is +@option{-mno-long-calls}. + +@item -mmad +@itemx -mno-mad +@opindex mmad +@opindex mno-mad +Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} +instructions, as provided by the R4650 ISA@. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Enable (disable) use of the floating point multiply-accumulate +instructions, when they are available. The default is +@option{-mfused-madd}. + +When multiply-accumulate instructions are used, the intermediate +product is calculated to infinite precision and is not subject to +the FCSR Flush to Zero bit. This may be undesirable in some +circumstances. + +@item -nocpp +@opindex nocpp +Tell the MIPS assembler to not run its preprocessor over user +assembler files (with a @samp{.s} suffix) when assembling them. + +@item -mfix-r4000 +@itemx -mno-fix-r4000 +@opindex mfix-r4000 +@opindex mno-fix-r4000 +Work around certain R4000 CPU errata: +@itemize @minus +@item +A double-word or a variable shift may give an incorrect result if executed +immediately after starting an integer division. +@item +A double-word or a variable shift may give an incorrect result if executed +while an integer multiplication is in progress. +@item +An integer division may give an incorrect result if started in a delay slot +of a taken branch or a jump. +@end itemize + +@item -mfix-r4400 +@itemx -mno-fix-r4400 +@opindex mfix-r4400 +@opindex mno-fix-r4400 +Work around certain R4400 CPU errata: +@itemize @minus +@item +A double-word or a variable shift may give an incorrect result if executed +immediately after starting an integer division. +@end itemize + +@item -mfix-vr4120 +@itemx -mno-fix-vr4120 +@opindex mfix-vr4120 +Work around certain VR4120 errata: +@itemize @minus +@item +@code{dmultu} does not always produce the correct result. +@item +@code{div} and @code{ddiv} do not always produce the correct result if one +of the operands is negative. +@end itemize +The workarounds for the division errata rely on special functions in +@file{libgcc.a}. At present, these functions are only provided by +the @code{mips64vr*-elf} configurations. + +Other VR4120 errata require a nop to be inserted between certain pairs of +instructions. These errata are handled by the assembler, not by GCC itself. + +@item -mfix-vr4130 +@opindex mfix-vr4130 +Work around the VR4130 @code{mflo}/@code{mfhi} errata. The +workarounds are implemented by the assembler rather than by GCC, +although GCC will avoid using @code{mflo} and @code{mfhi} if the +VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} +instructions are available instead. + +@item -mfix-sb1 +@itemx -mno-fix-sb1 +@opindex mfix-sb1 +Work around certain SB-1 CPU core errata. +(This flag currently works around the SB-1 revision 2 +``F1'' and ``F2'' floating point errata.) + +@item -mflush-func=@var{func} +@itemx -mno-flush-func +@opindex mflush-func +Specifies the function to call to flush the I and D caches, or to not +call any such function. If called, the function must take the same +arguments as the common @code{_flush_func()}, that is, the address of the +memory range for which the cache is being flushed, the size of the +memory range, and the number 3 (to flush both caches). The default +depends on the target GCC was configured for, but commonly is either +@samp{_flush_func} or @samp{__cpu_flush}. + +@item -mbranch-likely +@itemx -mno-branch-likely +@opindex mbranch-likely +@opindex mno-branch-likely +Enable or disable use of Branch Likely instructions, regardless of the +default for the selected architecture. By default, Branch Likely +instructions may be generated if they are supported by the selected +architecture. An exception is for the MIPS32 and MIPS64 architectures +and processors which implement those architectures; for those, Branch +Likely instructions will not be generated by default because the MIPS32 +and MIPS64 architectures specifically deprecate their use. + +@item -mfp-exceptions +@itemx -mno-fp-exceptions +@opindex mfp-exceptions +Specifies whether FP exceptions are enabled. This affects how we schedule +FP instructions for some processors. The default is that FP exceptions are +enabled. + +For instance, on the SB-1, if FP exceptions are disabled, and we are emitting +64-bit code, then we can use both FP pipes. Otherwise, we can only use one +FP pipe. + +@item -mvr4130-align +@itemx -mno-vr4130-align +@opindex mvr4130-align +The VR4130 pipeline is two-way superscalar, but can only issue two +instructions together if the first one is 8-byte aligned. When this +option is enabled, GCC will align pairs of instructions that it +thinks should execute in parallel. + +This option only has an effect when optimizing for the VR4130. +It normally makes code faster, but at the expense of making it bigger. +It is enabled by default at optimization level @option{-O3}. +@end table + +@node MMIX Options +@subsection MMIX Options +@cindex MMIX Options + +These options are defined for the MMIX: + +@table @gcctabopt +@item -mlibfuncs +@itemx -mno-libfuncs +@opindex mlibfuncs +@opindex mno-libfuncs +Specify that intrinsic library functions are being compiled, passing all +values in registers, no matter the size. + +@item -mepsilon +@itemx -mno-epsilon +@opindex mepsilon +@opindex mno-epsilon +Generate floating-point comparison instructions that compare with respect +to the @code{rE} epsilon register. + +@item -mabi=mmixware +@itemx -mabi=gnu +@opindex mabi-mmixware +@opindex mabi=gnu +Generate code that passes function parameters and return values that (in +the called function) are seen as registers @code{$0} and up, as opposed to +the GNU ABI which uses global registers @code{$231} and up. + +@item -mzero-extend +@itemx -mno-zero-extend +@opindex mzero-extend +@opindex mno-zero-extend +When reading data from memory in sizes shorter than 64 bits, use (do not +use) zero-extending load instructions by default, rather than +sign-extending ones. + +@item -mknuthdiv +@itemx -mno-knuthdiv +@opindex mknuthdiv +@opindex mno-knuthdiv +Make the result of a division yielding a remainder have the same sign as +the divisor. With the default, @option{-mno-knuthdiv}, the sign of the +remainder follows the sign of the dividend. Both methods are +arithmetically valid, the latter being almost exclusively used. + +@item -mtoplevel-symbols +@itemx -mno-toplevel-symbols +@opindex mtoplevel-symbols +@opindex mno-toplevel-symbols +Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly +code can be used with the @code{PREFIX} assembly directive. + +@item -melf +@opindex melf +Generate an executable in the ELF format, rather than the default +@samp{mmo} format used by the @command{mmix} simulator. + +@item -mbranch-predict +@itemx -mno-branch-predict +@opindex mbranch-predict +@opindex mno-branch-predict +Use (do not use) the probable-branch instructions, when static branch +prediction indicates a probable branch. + +@item -mbase-addresses +@itemx -mno-base-addresses +@opindex mbase-addresses +@opindex mno-base-addresses +Generate (do not generate) code that uses @emph{base addresses}. Using a +base address automatically generates a request (handled by the assembler +and the linker) for a constant to be set up in a global register. The +register is used for one or more base address requests within the range 0 +to 255 from the value held in the register. The generally leads to short +and fast code, but the number of different data items that can be +addressed is limited. This means that a program that uses lots of static +data may require @option{-mno-base-addresses}. + +@item -msingle-exit +@itemx -mno-single-exit +@opindex msingle-exit +@opindex mno-single-exit +Force (do not force) generated code to have a single exit point in each +function. +@end table + +@node MN10300 Options +@subsection MN10300 Options +@cindex MN10300 options + +These @option{-m} options are defined for Matsushita MN10300 architectures: + +@table @gcctabopt +@item -mmult-bug +@opindex mmult-bug +Generate code to avoid bugs in the multiply instructions for the MN10300 +processors. This is the default. + +@item -mno-mult-bug +@opindex mno-mult-bug +Do not generate code to avoid bugs in the multiply instructions for the +MN10300 processors. + +@item -mam33 +@opindex mam33 +Generate code which uses features specific to the AM33 processor. + +@item -mno-am33 +@opindex mno-am33 +Do not generate code which uses features specific to the AM33 processor. This +is the default. + +@item -mreturn-pointer-on-d0 +@opindex mreturn-pointer-on-d0 +When generating a function which returns a pointer, return the pointer +in both @code{a0} and @code{d0}. Otherwise, the pointer is returned +only in a0, and attempts to call such functions without a prototype +would result in errors. Note that this option is on by default; use +@option{-mno-return-pointer-on-d0} to disable it. + +@item -mno-crt0 +@opindex mno-crt0 +Do not link in the C run-time initialization object file. + +@item -mrelax +@opindex mrelax +Indicate to the linker that it should perform a relaxation optimization pass +to shorten branches, calls and absolute memory addresses. This option only +has an effect when used on the command line for the final link step. + +This option makes symbolic debugging impossible. +@end table + +@node MT Options +@subsection MT Options +@cindex MT options + +These @option{-m} options are defined for Morpho MT architectures: + +@table @gcctabopt + +@item -march=@var{cpu-type} +@opindex march +Generate code that will run on @var{cpu-type}, which is the name of a system +representing a certain processor type. Possible values for +@var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002}, +@samp{ms1-16-003} and @samp{ms2}. + +When this option is not used, the default is @option{-march=ms1-16-002}. + +@item -mbacc +@opindex mbacc +Use byte loads and stores when generating code. + +@item -mno-bacc +@opindex mno-bacc +Do not use byte loads and stores when generating code. + +@item -msim +@opindex msim +Use simulator runtime + +@item -mno-crt0 +@opindex mno-crt0 +Do not link in the C run-time initialization object file +@file{crti.o}. Other run-time initialization and termination files +such as @file{startup.o} and @file{exit.o} are still included on the +linker command line. + +@end table + +@node PDP-11 Options +@subsection PDP-11 Options +@cindex PDP-11 Options + +These options are defined for the PDP-11: + +@table @gcctabopt +@item -mfpu +@opindex mfpu +Use hardware FPP floating point. This is the default. (FIS floating +point on the PDP-11/40 is not supported.) + +@item -msoft-float +@opindex msoft-float +Do not use hardware floating point. + +@item -mac0 +@opindex mac0 +Return floating-point results in ac0 (fr0 in Unix assembler syntax). + +@item -mno-ac0 +@opindex mno-ac0 +Return floating-point results in memory. This is the default. + +@item -m40 +@opindex m40 +Generate code for a PDP-11/40. + +@item -m45 +@opindex m45 +Generate code for a PDP-11/45. This is the default. + +@item -m10 +@opindex m10 +Generate code for a PDP-11/10. + +@item -mbcopy-builtin +@opindex bcopy-builtin +Use inline @code{movmemhi} patterns for copying memory. This is the +default. + +@item -mbcopy +@opindex mbcopy +Do not use inline @code{movmemhi} patterns for copying memory. + +@item -mint16 +@itemx -mno-int32 +@opindex mint16 +@opindex mno-int32 +Use 16-bit @code{int}. This is the default. + +@item -mint32 +@itemx -mno-int16 +@opindex mint32 +@opindex mno-int16 +Use 32-bit @code{int}. + +@item -mfloat64 +@itemx -mno-float32 +@opindex mfloat64 +@opindex mno-float32 +Use 64-bit @code{float}. This is the default. + +@item -mfloat32 +@itemx -mno-float64 +@opindex mfloat32 +@opindex mno-float64 +Use 32-bit @code{float}. + +@item -mabshi +@opindex mabshi +Use @code{abshi2} pattern. This is the default. + +@item -mno-abshi +@opindex mno-abshi +Do not use @code{abshi2} pattern. + +@item -mbranch-expensive +@opindex mbranch-expensive +Pretend that branches are expensive. This is for experimenting with +code generation only. + +@item -mbranch-cheap +@opindex mbranch-cheap +Do not pretend that branches are expensive. This is the default. + +@item -msplit +@opindex msplit +Generate code for a system with split I&D@. + +@item -mno-split +@opindex mno-split +Generate code for a system without split I&D@. This is the default. + +@item -munix-asm +@opindex munix-asm +Use Unix assembler syntax. This is the default when configured for +@samp{pdp11-*-bsd}. + +@item -mdec-asm +@opindex mdec-asm +Use DEC assembler syntax. This is the default when configured for any +PDP-11 target other than @samp{pdp11-*-bsd}. +@end table +@c APPLE LOCAL prune man page +@end ignore + +@node PowerPC Options +@subsection PowerPC Options +@cindex PowerPC options + +These are listed under @xref{RS/6000 and PowerPC Options}. + +@node RS/6000 and PowerPC Options +@subsection IBM RS/6000 and PowerPC Options +@cindex RS/6000 and PowerPC Options +@cindex IBM RS/6000 and PowerPC Options + +These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: +@table @gcctabopt +@item -mpower +@itemx -mno-power +@itemx -mpower2 +@itemx -mno-power2 +@itemx -mpowerpc +@itemx -mno-powerpc +@itemx -mpowerpc-gpopt +@itemx -mno-powerpc-gpopt +@itemx -mpowerpc-gfxopt +@itemx -mno-powerpc-gfxopt +@itemx -mpowerpc64 +@itemx -mno-powerpc64 +@itemx -mmfcrf +@itemx -mno-mfcrf +@itemx -mpopcntb +@itemx -mno-popcntb +@itemx -mfprnd +@itemx -mno-fprnd +@opindex mpower +@opindex mno-power +@opindex mpower2 +@opindex mno-power2 +@opindex mpowerpc +@opindex mno-powerpc +@opindex mpowerpc-gpopt +@opindex mno-powerpc-gpopt +@opindex mpowerpc-gfxopt +@opindex mno-powerpc-gfxopt +@opindex mpowerpc64 +@opindex mno-powerpc64 +@opindex mmfcrf +@opindex mno-mfcrf +@opindex mpopcntb +@opindex mno-popcntb +@opindex mfprnd +@opindex mno-fprnd +GCC supports two related instruction set architectures for the +RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those +instructions supported by the @samp{rios} chip set used in the original +RS/6000 systems and the @dfn{PowerPC} instruction set is the +architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and +the IBM 4xx, 6xx, and follow-on microprocessors. + +Neither architecture is a subset of the other. However there is a +large common subset of instructions supported by both. An MQ +register is included in processors supporting the POWER architecture. + +You use these options to specify which instructions are available on the +processor you are using. The default value of these options is +determined when configuring GCC@. Specifying the +@option{-mcpu=@var{cpu_type}} overrides the specification of these +options. We recommend you use the @option{-mcpu=@var{cpu_type}} option +rather than the options listed above. + +The @option{-mpower} option allows GCC to generate instructions that +are found only in the POWER architecture and to use the MQ register. +Specifying @option{-mpower2} implies @option{-power} and also allows GCC +to generate instructions that are present in the POWER2 architecture but +not the original POWER architecture. + +The @option{-mpowerpc} option allows GCC to generate instructions that +are found only in the 32-bit subset of the PowerPC architecture. +Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows +GCC to use the optional PowerPC architecture instructions in the +General Purpose group, including floating-point square root. Specifying +@option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to +use the optional PowerPC architecture instructions in the Graphics +group, including floating-point select. + +The @option{-mmfcrf} option allows GCC to generate the move from +condition register field instruction implemented on the POWER4 +processor and other processors that support the PowerPC V2.01 +architecture. +The @option{-mpopcntb} option allows GCC to generate the popcount and +double precision FP reciprocal estimate instruction implemented on the +POWER5 processor and other processors that support the PowerPC V2.02 +architecture. +The @option{-mfprnd} option allows GCC to generate the FP round to +integer instructions implemented on the POWER5+ processor and other +processors that support the PowerPC V2.03 architecture. + +The @option{-mpowerpc64} option allows GCC to generate the additional +64-bit instructions that are found in the full PowerPC64 architecture +and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to +@option{-mno-powerpc64}. + +If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC +will use only the instructions in the common subset of both +architectures plus some special AIX common-mode calls, and will not use +the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc} +permits GCC to use any instruction from either architecture and to +allow use of the MQ register; specify this for the Motorola MPC601. + +@item -mnew-mnemonics +@itemx -mold-mnemonics +@opindex mnew-mnemonics +@opindex mold-mnemonics +Select which mnemonics to use in the generated assembler code. With +@option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for +the PowerPC architecture. With @option{-mold-mnemonics} it uses the +assembler mnemonics defined for the POWER architecture. Instructions +defined in only one architecture have only one mnemonic; GCC uses that +mnemonic irrespective of which of these options is specified. + +GCC defaults to the mnemonics appropriate for the architecture in +use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the +value of these option. Unless you are building a cross-compiler, you +should normally not specify either @option{-mnew-mnemonics} or +@option{-mold-mnemonics}, but should instead accept the default. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set architecture type, register usage, choice of mnemonics, and +instruction scheduling parameters for machine type @var{cpu_type}. +Supported values for @var{cpu_type} are @samp{401}, @samp{403}, +@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505}, +@samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604}, +@samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400}, +@samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, +@samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3}, +@samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3}, +@samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6}, +@samp{common}, @samp{powerpc}, @samp{powerpc64}, +@samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}. + +@option{-mcpu=common} selects a completely generic processor. Code +generated under this option will run on any POWER or PowerPC processor. +GCC will use only the instructions in the common subset of both +architectures, and will not use the MQ register. GCC assumes a generic +processor model for scheduling purposes. + +@option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and +@option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit +PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine +types, with an appropriate, generic processor model assumed for +scheduling purposes. + +The other options specify a specific processor. Code generated under +those options will run best on that processor, and may not run at all on +others. + +The @option{-mcpu} options automatically enable or disable the +following options: @option{-maltivec}, @option{-mfprnd}, +@option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple}, +@option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower}, +@option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt}, +@option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}, @option{-mdlmzb}. +The particular options +set for any particular CPU will vary between compiler versions, +depending on what setting seems to produce optimal code for that CPU; +it doesn't necessarily reflect the actual hardware's capabilities. If +you wish to set an individual option to a particular value, you may +specify it after the @option{-mcpu} option, like @samp{-mcpu=970 +-mno-altivec}. + +On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are +not enabled or disabled by the @option{-mcpu} option at present because +AIX does not have full support for these options. You may still +enable or disable them individually if you're sure it'll work in your +environment. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the architecture type, register usage, or +choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same +values for @var{cpu_type} are used for @option{-mtune} as for +@option{-mcpu}. If both are specified, the code generated will use the +architecture, registers, and mnemonics set by @option{-mcpu}, but the +scheduling parameters set by @option{-mtune}. + +@item -mswdiv +@itemx -mno-swdiv +@opindex mswdiv +@opindex mno-swdiv +Generate code to compute division as reciprocal estimate and iterative +refinement, creating opportunities for increased throughput. This +feature requires: optional PowerPC Graphics instruction set for single +precision and FRE instruction for double precision, assuming divides +cannot generate user-visible traps, and the domain values not include +Infinities, denormals or zero denominator. + +@item -maltivec +@itemx -mno-altivec +@opindex maltivec +@opindex mno-altivec +Generate code that uses (does not use) AltiVec instructions, and also +enable the use of built-in functions that allow more direct access to +the AltiVec instruction set. You may also need to set +@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI +enhancements. + +@c APPLE LOCAL begin AltiVec +@item -mpim-altivec +@itemx -mno-pim-altivec +@opindex mpim-altivec +@opindex mno-pim-altivec +Enable (or disable) built-in compiler support for the syntactic extensions as +well as operations and predicates defined in the Motorola AltiVec +Technology Programming Interface Manual (PIM). This includes the +recognition of @code{vector} and @code{pixel} as (context-dependent) +keywords, the definition of built-in functions such as @code{vec_add}, +and the use of parenthesized comma expression as AltiVec literals. +Note that unlike the option @option{-maltivec}, the extension does not require +the inclusion of any special header files; if @code{<altivec.h>} is included, +a warning will be issued and the contents of the header will be +ignored. The preprocessor shall provide an @code{__APPLE_ALTIVEC__} +manifest constant when @option{-mpim-altivec} is specified. (APPLE ONLY) + +In addition, the @option{-mpim-altivec} option disables the inlining of +functions containing AltiVec instructions into functions that do not make +use of the vector unit. Certain other optimizations, such as inline +vectorization of @code{memset} and @code{memcpy} calls, are also disabled. +These adjustments make it possible to compile programs whose use of AltiVec +instructions is preceded by a run-time check for the presence of AltiVec +functionality, and that can therefore be made to run on G3 processors. +Note that all of these optimizations may be re-enabled by supplying +the @option{-maltivec} option, or an @option{-mcpu} option specifying +a processor that supports AltiVec instructions. +@c APPLE LOCAL end AltiVec + +@item -mvrsave +@item -mno-vrsave +@opindex mvrsave +@opindex mno-vrsave +Generate VRSAVE instructions when generating AltiVec code. + +@item -msecure-plt +@opindex msecure-plt +Generate code that allows ld and ld.so to build executables and shared +libraries with non-exec .plt and .got sections. This is a PowerPC +32-bit SYSV ABI option. + +@item -mbss-plt +@opindex mbss-plt +Generate code that uses a BSS .plt section that ld.so fills in, and +requires .plt and .got sections that are both writable and executable. +This is a PowerPC 32-bit SYSV ABI option. + +@item -misel +@itemx -mno-isel +@opindex misel +@opindex mno-isel +This switch enables or disables the generation of ISEL instructions. + +@item -misel=@var{yes/no} +This switch has been deprecated. Use @option{-misel} and +@option{-mno-isel} instead. + +@item -mspe +@itemx -mno-spe +@opindex mspe +@opindex mno-spe +This switch enables or disables the generation of SPE simd +instructions. + +@item -mspe=@var{yes/no} +This option has been deprecated. Use @option{-mspe} and +@option{-mno-spe} instead. + +@item -mfloat-gprs=@var{yes/single/double/no} +@itemx -mfloat-gprs +@opindex mfloat-gprs +This switch enables or disables the generation of floating point +operations on the general purpose registers for architectures that +support it. + +The argument @var{yes} or @var{single} enables the use of +single-precision floating point operations. + +The argument @var{double} enables the use of single and +double-precision floating point operations. + +The argument @var{no} disables floating point operations on the +general purpose registers. + +This option is currently only available on the MPC854x. + +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for 32-bit or 64-bit environments of Darwin and SVR4 +targets (including GNU/Linux). The 32-bit environment sets int, long +and pointer to 32 bits and generates code that runs on any PowerPC +variant. The 64-bit environment sets int to 32 bits and long and +pointer to 64 bits, and generates code for PowerPC64, as for +@option{-mpowerpc64}. + +@item -mfull-toc +@itemx -mno-fp-in-toc +@itemx -mno-sum-in-toc +@itemx -mminimal-toc +@opindex mfull-toc +@opindex mno-fp-in-toc +@opindex mno-sum-in-toc +@opindex mminimal-toc +Modify generation of the TOC (Table Of Contents), which is created for +every executable file. The @option{-mfull-toc} option is selected by +default. In that case, GCC will allocate at least one TOC entry for +each unique non-automatic variable reference in your program. GCC +will also place floating-point constants in the TOC@. However, only +16,384 entries are available in the TOC@. + +If you receive a linker error message that saying you have overflowed +the available TOC space, you can reduce the amount of TOC space used +with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. +@option{-mno-fp-in-toc} prevents GCC from putting floating-point +constants in the TOC and @option{-mno-sum-in-toc} forces GCC to +generate code to calculate the sum of an address and a constant at +run-time instead of putting that sum into the TOC@. You may specify one +or both of these options. Each causes GCC to produce very slightly +slower and larger code at the expense of conserving TOC space. + +If you still run out of space in the TOC even when you specify both of +these options, specify @option{-mminimal-toc} instead. This option causes +GCC to make only one TOC entry for every file. When you specify this +option, GCC will produce code that is slower and larger but which +uses extremely little TOC space. You may wish to use this option +only on files that contain less frequently executed code. + +@item -maix64 +@itemx -maix32 +@opindex maix64 +@opindex maix32 +Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit +@code{long} type, and the infrastructure needed to support them. +Specifying @option{-maix64} implies @option{-mpowerpc64} and +@option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and +implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. + +@item -mxl-compat +@itemx -mno-xl-compat +@opindex mxl-compat +@opindex mno-xl-compat +Produce code that conforms more closely to IBM XL compiler semantics +when using AIX-compatible ABI. Pass floating-point arguments to +prototyped functions beyond the register save area (RSA) on the stack +in addition to argument FPRs. Do not assume that most significant +double in 128-bit long double value is properly rounded when comparing +values and converting to double. Use XL symbol names for long double +support routines. + +The AIX calling convention was extended but not initially documented to +handle an obscure K&R C case of calling a function that takes the +address of its arguments with fewer arguments than declared. IBM XL +compilers access floating point arguments which do not fit in the +RSA from the stack when a subroutine is compiled without +optimization. Because always storing floating-point arguments on the +stack is inefficient and rarely needed, this option is not enabled by +default and only is necessary when calling subroutines compiled by IBM +XL compilers without optimization. + +@item -mpe +@opindex mpe +Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an +application written to use message passing with special startup code to +enable the application to run. The system must have PE installed in the +standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file +must be overridden with the @option{-specs=} option to specify the +appropriate directory location. The Parallel Environment does not +support threads, so the @option{-mpe} option and the @option{-pthread} +option are incompatible. + +@item -malign-natural +@itemx -malign-power +@opindex malign-natural +@opindex malign-power +On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option +@option{-malign-natural} overrides the ABI-defined alignment of larger +types, such as floating-point doubles, on their natural size-based boundary. +The option @option{-malign-power} instructs GCC to follow the ABI-specified +alignment rules. GCC defaults to the standard alignment defined in the ABI@. + +On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} +is not supported. + +@item -msoft-float +@itemx -mhard-float +@opindex msoft-float +@opindex mhard-float +Generate code that does not use (uses) the floating-point register set. +Software floating point emulation is provided if you use the +@option{-msoft-float} option, and pass the option to GCC when linking. + +@c APPLE LOCAL begin describe actual behavior 3888787 +(APPLE ONLY) While the -msoft-float option is supported, the libraries that +do the floating point emulation are not shipped on Apple PowerPCs, with the +effect that the emulation does not work. However, the option +may be useful for a different reason. Normally the compiler can use floating +point registers in contexts where you might not expect it, for example, to +copy data from one memory location to another. The -msoft-float option will +prevent it from doing this. +@c APPLE LOCAL end describe actual behavior 3888787 + +@item -mmultiple +@itemx -mno-multiple +@opindex mmultiple +@opindex mno-multiple +Generate code that uses (does not use) the load multiple word +instructions and the store multiple word instructions. These +instructions are generated by default on POWER systems, and not +generated on PowerPC systems. Do not use @option{-mmultiple} on little +endian PowerPC systems, since those instructions do not work when the +processor is in little endian mode. The exceptions are PPC740 and +PPC750 which permit the instructions usage in little endian mode. + +@item -mstring +@itemx -mno-string +@opindex mstring +@opindex mno-string +Generate code that uses (does not use) the load string instructions +and the store string word instructions to save multiple registers and +do small block moves. These instructions are generated by default on +POWER systems, and not generated on PowerPC systems. Do not use +@option{-mstring} on little endian PowerPC systems, since those +instructions do not work when the processor is in little endian mode. +The exceptions are PPC740 and PPC750 which permit the instructions +usage in little endian mode. + +@item -mupdate +@itemx -mno-update +@opindex mupdate +@opindex mno-update +Generate code that uses (does not use) the load or store instructions +that update the base register to the address of the calculated memory +location. These instructions are generated by default. If you use +@option{-mno-update}, there is a small window between the time that the +stack pointer is updated and the address of the previous frame is +stored, which means code that walks the stack frame across interrupts or +signals may get corrupted data. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating point multiply and +accumulate instructions. These instructions are generated by default if +hardware floating is used. + +@item -mmulhw +@itemx -mno-mulhw +@opindex mmulhw +@opindex mno-mulhw +Generate code that uses (does not use) the half-word multiply and +multiply-accumulate instructions on the IBM 405 and 440 processors. +These instructions are generated by default when targetting those +processors. + +@item -mdlmzb +@itemx -mno-dlmzb +@opindex mdlmzb +@opindex mno-dlmzb +Generate code that uses (does not use) the string-search @samp{dlmzb} +instruction on the IBM 405 and 440 processors. This instruction is +generated by default when targetting those processors. + +@item -mno-bit-align +@itemx -mbit-align +@opindex mno-bit-align +@opindex mbit-align +On System V.4 and embedded PowerPC systems do not (do) force structures +and unions that contain bit-fields to be aligned to the base type of the +bit-field. + +For example, by default a structure containing nothing but 8 +@code{unsigned} bit-fields of length 1 would be aligned to a 4 byte +boundary and have a size of 4 bytes. By using @option{-mno-bit-align}, +the structure would be aligned to a 1 byte boundary and be one byte in +size. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +On System V.4 and embedded PowerPC systems do not (do) assume that +unaligned memory references will be handled by the system. + +@item -mrelocatable +@itemx -mno-relocatable +@opindex mrelocatable +@opindex mno-relocatable +On embedded PowerPC systems generate code that allows (does not allow) +the program to be relocated to a different address at runtime. If you +use @option{-mrelocatable} on any module, all objects linked together must +be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}. + +@item -mrelocatable-lib +@itemx -mno-relocatable-lib +@opindex mrelocatable-lib +@opindex mno-relocatable-lib +On embedded PowerPC systems generate code that allows (does not allow) +the program to be relocated to a different address at runtime. Modules +compiled with @option{-mrelocatable-lib} can be linked with either modules +compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or +with modules compiled with the @option{-mrelocatable} options. + +@item -mno-toc +@itemx -mtoc +@opindex mno-toc +@opindex mtoc +On System V.4 and embedded PowerPC systems do not (do) assume that +register 2 contains a pointer to a global area pointing to the addresses +used in the program. + +@item -mlittle +@itemx -mlittle-endian +@opindex mlittle +@opindex mlittle-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in little endian mode. The @option{-mlittle-endian} option is +the same as @option{-mlittle}. + +@item -mbig +@itemx -mbig-endian +@opindex mbig +@opindex mbig-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in big endian mode. The @option{-mbig-endian} option is +the same as @option{-mbig}. + +@item -mdynamic-no-pic +@opindex mdynamic-no-pic +On Darwin and Mac OS X systems, compile code so that it is not +relocatable, but that its external references are relocatable. The +resulting code is suitable for applications, but not shared +libraries. + +@item -mprioritize-restricted-insns=@var{priority} +@opindex mprioritize-restricted-insns +This option controls the priority that is assigned to +dispatch-slot restricted instructions during the second scheduling +pass. The argument @var{priority} takes the value @var{0/1/2} to assign +@var{no/highest/second-highest} priority to dispatch slot restricted +instructions. + +@item -msched-costly-dep=@var{dependence_type} +@opindex msched-costly-dep +This option controls which dependences are considered costly +by the target during instruction scheduling. The argument +@var{dependence_type} takes one of the following values: +@var{no}: no dependence is costly, +@var{all}: all dependences are costly, +@var{true_store_to_load}: a true dependence from store to load is costly, +@var{store_to_load}: any dependence from store to load is costly, +@var{number}: any dependence which latency >= @var{number} is costly. + +@item -minsert-sched-nops=@var{scheme} +@opindex minsert-sched-nops +This option controls which nop insertion scheme will be used during +the second scheduling pass. The argument @var{scheme} takes one of the +following values: +@var{no}: Don't insert nops. +@var{pad}: Pad with nops any dispatch group which has vacant issue slots, +according to the scheduler's grouping. +@var{regroup_exact}: Insert nops to force costly dependent insns into +separate groups. Insert exactly as many nops as needed to force an insn +to a new group, according to the estimated processor grouping. +@var{number}: Insert nops to force costly dependent insns into +separate groups. Insert @var{number} nops to force an insn to a new group. + +@item -mcall-sysv +@opindex mcall-sysv +On System V.4 and embedded PowerPC systems compile code using calling +conventions that adheres to the March 1995 draft of the System V +Application Binary Interface, PowerPC processor supplement. This is the +default unless you configured GCC using @samp{powerpc-*-eabiaix}. + +@item -mcall-sysv-eabi +@opindex mcall-sysv-eabi +Specify both @option{-mcall-sysv} and @option{-meabi} options. + +@item -mcall-sysv-noeabi +@opindex mcall-sysv-noeabi +Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. + +@item -mcall-solaris +@opindex mcall-solaris +On System V.4 and embedded PowerPC systems compile code for the Solaris +operating system. + +@item -mcall-linux +@opindex mcall-linux +On System V.4 and embedded PowerPC systems compile code for the +Linux-based GNU system. + +@item -mcall-gnu +@opindex mcall-gnu +On System V.4 and embedded PowerPC systems compile code for the +Hurd-based GNU system. + +@item -mcall-netbsd +@opindex mcall-netbsd +On System V.4 and embedded PowerPC systems compile code for the +NetBSD operating system. + +@item -maix-struct-return +@opindex maix-struct-return +Return all structures in memory (as specified by the AIX ABI)@. + +@item -msvr4-struct-return +@opindex msvr4-struct-return +Return structures smaller than 8 bytes in registers (as specified by the +SVR4 ABI)@. + +@item -mabi=@var{abi-type} +@opindex mabi +Extend the current ABI with a particular extension, or remove such extension. +Valid values are @var{altivec}, @var{no-altivec}, @var{spe}, +@var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@. + +@item -mabi=spe +@opindex mabi=spe +Extend the current ABI with SPE ABI extensions. This does not change +the default ABI, instead it adds the SPE ABI extensions to the current +ABI@. + +@item -mabi=no-spe +@opindex mabi=no-spe +Disable Booke SPE ABI extensions for the current ABI@. + +@item -mabi=ibmlongdouble +@opindex mabi=ibmlongdouble +Change the current ABI to use IBM extended precision long double. +This is a PowerPC 32-bit SYSV ABI option. + +@item -mabi=ieeelongdouble +@opindex mabi=ieeelongdouble +Change the current ABI to use IEEE extended precision long double. +This is a PowerPC 32-bit Linux ABI option. + +@item -mprototype +@itemx -mno-prototype +@opindex mprototype +@opindex mno-prototype +On System V.4 and embedded PowerPC systems assume that all calls to +variable argument functions are properly prototyped. Otherwise, the +compiler must insert an instruction before every non prototyped call to +set or clear bit 6 of the condition code register (@var{CR}) to +indicate whether floating point values were passed in the floating point +registers in case the function takes a variable arguments. With +@option{-mprototype}, only calls to prototyped variable argument functions +will set or clear the bit. + +@item -msim +@opindex msim +On embedded PowerPC systems, assume that the startup module is called +@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and +@file{libc.a}. This is the default for @samp{powerpc-*-eabisim}. +configurations. + +@item -mmvme +@opindex mmvme +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libmvme.a} and +@file{libc.a}. + +@item -mads +@opindex mads +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libads.a} and +@file{libc.a}. + +@item -myellowknife +@opindex myellowknife +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libyk.a} and +@file{libc.a}. + +@item -mvxworks +@opindex mvxworks +On System V.4 and embedded PowerPC systems, specify that you are +compiling for a VxWorks system. + +@item -mwindiss +@opindex mwindiss +Specify that you are compiling for the WindISS simulation environment. + +@item -memb +@opindex memb +On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags +header to indicate that @samp{eabi} extended relocations are used. + +@item -meabi +@itemx -mno-eabi +@opindex meabi +@opindex mno-eabi +On System V.4 and embedded PowerPC systems do (do not) adhere to the +Embedded Applications Binary Interface (eabi) which is a set of +modifications to the System V.4 specifications. Selecting @option{-meabi} +means that the stack is aligned to an 8 byte boundary, a function +@code{__eabi} is called to from @code{main} to set up the eabi +environment, and the @option{-msdata} option can use both @code{r2} and +@code{r13} to point to two separate small data areas. Selecting +@option{-mno-eabi} means that the stack is aligned to a 16 byte boundary, +do not call an initialization function from @code{main}, and the +@option{-msdata} option will only use @code{r13} to point to a single +small data area. The @option{-meabi} option is on by default if you +configured GCC using one of the @samp{powerpc*-*-eabi*} options. + +@item -msdata=eabi +@opindex msdata=eabi +On System V.4 and embedded PowerPC systems, put small initialized +@code{const} global and static data in the @samp{.sdata2} section, which +is pointed to by register @code{r2}. Put small initialized +non-@code{const} global and static data in the @samp{.sdata} section, +which is pointed to by register @code{r13}. Put small uninitialized +global and static data in the @samp{.sbss} section, which is adjacent to +the @samp{.sdata} section. The @option{-msdata=eabi} option is +incompatible with the @option{-mrelocatable} option. The +@option{-msdata=eabi} option also sets the @option{-memb} option. + +@item -msdata=sysv +@opindex msdata=sysv +On System V.4 and embedded PowerPC systems, put small global and static +data in the @samp{.sdata} section, which is pointed to by register +@code{r13}. Put small uninitialized global and static data in the +@samp{.sbss} section, which is adjacent to the @samp{.sdata} section. +The @option{-msdata=sysv} option is incompatible with the +@option{-mrelocatable} option. + +@item -msdata=default +@itemx -msdata +@opindex msdata=default +@opindex msdata +On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, +compile code the same as @option{-msdata=eabi}, otherwise compile code the +same as @option{-msdata=sysv}. + +@item -msdata-data +@opindex msdata-data +On System V.4 and embedded PowerPC systems, put small global +data in the @samp{.sdata} section. Put small uninitialized global +data in the @samp{.sbss} section. Do not use register @code{r13} +to address small data however. This is the default behavior unless +other @option{-msdata} options are used. + +@item -msdata=none +@itemx -mno-sdata +@opindex msdata=none +@opindex mno-sdata +On embedded PowerPC systems, put all initialized global and static data +in the @samp{.data} section, and all uninitialized data in the +@samp{.bss} section. + +@item -G @var{num} +@opindex G +@cindex smaller data references (PowerPC) +@cindex .sdata/.sdata2 references (PowerPC) +On embedded PowerPC systems, put global and static items less than or +equal to @var{num} bytes into the small data or bss sections instead of +the normal data or bss section. By default, @var{num} is 8. The +@option{-G @var{num}} switch is also passed to the linker. +All modules should be compiled with the same @option{-G @var{num}} value. + +@item -mregnames +@itemx -mno-regnames +@opindex mregnames +@opindex mno-regnames +On System V.4 and embedded PowerPC systems do (do not) emit register +names in the assembly language output using symbolic forms. + +@item -mlongcall +@itemx -mno-longcall +@opindex mlongcall +@opindex mno-longcall +@c APPLE LOCAL begin 4222119 +@itemx -mlong-branch +@itemx -mno-long-branch +@opindex mlong-branch +@opindex mno-long-branch +@c APPLE LOCAL end 4222119 +By default assume that all calls are far away so that a longer more +expensive calling sequence is required. This is required for calls +further than 32 megabytes (33,554,432 bytes) from the current location. +A short call will be generated if the compiler knows +the call cannot be that far away. This setting can be overridden by +the @code{shortcall} function attribute, or by @code{#pragma +longcall(0)}. + +Some linkers are capable of detecting out-of-range calls and generating +glue code on the fly. On these systems, long calls are unnecessary and +generate slower code. As of this writing, the AIX linker can do this, +as can the GNU linker for PowerPC/64. It is planned to add this feature +to the GNU linker for 32-bit PowerPC systems as well. + +On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr +callee, L42'', plus a ``branch island'' (glue code). The two target +addresses represent the callee and the ``branch island''. The +Darwin/PPC linker will prefer the first address and generate a ``bl +callee'' if the PPC ``bl'' instruction will reach the callee directly; +otherwise, the linker will generate ``bl L42'' to call the ``branch +island''. The ``branch island'' is appended to the body of the +calling function; it computes the full 32-bit address of the callee +and jumps to it. + +@c APPLE LOCAL begin 4222119 +On Mach-O (Darwin) systems, @option{-mlongcall} directs the compiler +emit to the glue for every direct call, and the Darwin linker decides +whether to use or discard it. @option{-mlong-branch} is a synonym for +@option{-mlongcall}. +@c APPLE LOCAL end 4222119 + +In the future, we may cause GCC to ignore all longcall specifications +when the linker is known to generate glue. + +@item -pthread +@opindex pthread +Adds support for multithreading with the @dfn{pthreads} library. +This option sets flags for both the preprocessor and linker. + +@c APPLE LOCAL begin 5946347 ms_struct support +@item -mms-bitfields +@opindex mms-bitfields +Set the default structure layout to be compatible with the Microsoft +compiler standard. This is equivalent to adding an @code{ms_struct} +attribute to each structure and union tag definition. The default is +@option{mno-ms-bitfields}. +@c APPLE LOCAL end 5946347 ms_struct support + +@end table + +@c APPLE LOCAL prune man page +@ignore +@node S/390 and zSeries Options +@subsection S/390 and zSeries Options +@cindex S/390 and zSeries Options + +These are the @samp{-m} options defined for the S/390 and zSeries architecture. + +@table @gcctabopt +@item -mhard-float +@itemx -msoft-float +@opindex mhard-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions and registers +for floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} will be used to perform floating-point +operations. When @option{-mhard-float} is specified, the compiler +generates IEEE floating-point instructions. This is the default. + +@item -mlong-double-64 +@itemx -mlong-double-128 +@opindex mlong-double-64 +@opindex mlong-double-128 +These switches control the size of @code{long double} type. A size +of 64bit makes the @code{long double} type equivalent to the @code{double} +type. This is the default. + +@item -mbackchain +@itemx -mno-backchain +@opindex mbackchain +@opindex mno-backchain +Store (do not store) the address of the caller's frame as backchain pointer +into the callee's stack frame. +A backchain may be needed to allow debugging using tools that do not understand +DWARF-2 call frame information. +When @option{-mno-packed-stack} is in effect, the backchain pointer is stored +at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, +the backchain is placed into the topmost word of the 96/160 byte register +save area. + +In general, code compiled with @option{-mbackchain} is call-compatible with +code compiled with @option{-mmo-backchain}; however, use of the backchain +for debugging purposes usually requires that the whole binary is built with +@option{-mbackchain}. Note that the combination of @option{-mbackchain}, +@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order +to build a linux kernel use @option{-msoft-float}. + +The default is to not maintain the backchain. + +@item -mpacked-stack +@item -mno-packed-stack +@opindex mpacked-stack +@opindex mno-packed-stack +Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is +specified, the compiler uses the all fields of the 96/160 byte register save +area only for their default purpose; unused fields still take up stack space. +When @option{-mpacked-stack} is specified, register save slots are densely +packed at the top of the register save area; unused space is reused for other +purposes, allowing for more efficient use of the available stack space. +However, when @option{-mbackchain} is also in effect, the topmost word of +the save area is always used to store the backchain, and the return address +register is always saved two words below the backchain. + +As long as the stack frame backchain is not used, code generated with +@option{-mpacked-stack} is call-compatible with code generated with +@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for +S/390 or zSeries generated code that uses the stack frame backchain at run +time, not just for debugging purposes. Such code is not call-compatible +with code compiled with @option{-mpacked-stack}. Also, note that the +combination of @option{-mbackchain}, +@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order +to build a linux kernel use @option{-msoft-float}. + +The default is to not use the packed stack layout. + +@item -msmall-exec +@itemx -mno-small-exec +@opindex msmall-exec +@opindex mno-small-exec +Generate (or do not generate) code using the @code{bras} instruction +to do subroutine calls. +This only works reliably if the total executable size does not +exceed 64k. The default is to use the @code{basr} instruction instead, +which does not have this limitation. + +@item -m64 +@itemx -m31 +@opindex m64 +@opindex m31 +When @option{-m31} is specified, generate code compliant to the +GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate +code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in +particular to generate 64-bit instructions. For the @samp{s390} +targets, the default is @option{-m31}, while the @samp{s390x} +targets default to @option{-m64}. + +@item -mzarch +@itemx -mesa +@opindex mzarch +@opindex mesa +When @option{-mzarch} is specified, generate code using the +instructions available on z/Architecture. +When @option{-mesa} is specified, generate code using the +instructions available on ESA/390. Note that @option{-mesa} is +not possible with @option{-m64}. +When generating code compliant to the GNU/Linux for S/390 ABI, +the default is @option{-mesa}. When generating code compliant +to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. + +@item -mmvcle +@itemx -mno-mvcle +@opindex mmvcle +@opindex mno-mvcle +Generate (or do not generate) code using the @code{mvcle} instruction +to perform block moves. When @option{-mno-mvcle} is specified, +use a @code{mvc} loop instead. This is the default unless optimizing for +size. + +@item -mdebug +@itemx -mno-debug +@opindex mdebug +@opindex mno-debug +Print (or do not print) additional debug information when compiling. +The default is to not print debug information. + +@item -march=@var{cpu-type} +@opindex march +Generate code that will run on @var{cpu-type}, which is the name of a system +representing a certain processor type. Possible values for +@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}. +When generating code using the instructions available on z/Architecture, +the default is @option{-march=z900}. Otherwise, the default is +@option{-march=g5}. + +@item -mtune=@var{cpu-type} +@opindex mtune +Tune to @var{cpu-type} everything applicable about the generated code, +except for the ABI and the set of available instructions. +The list of @var{cpu-type} values is the same as for @option{-march}. +The default is the value used for @option{-march}. + +@item -mtpf-trace +@itemx -mno-tpf-trace +@opindex mtpf-trace +@opindex mno-tpf-trace +Generate code that adds (does not add) in TPF OS specific branches to trace +routines in the operating system. This option is off by default, even +when compiling for the TPF OS@. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating point multiply and +accumulate instructions. These instructions are generated by default if +hardware floating point is used. + +@item -mwarn-framesize=@var{framesize} +@opindex mwarn-framesize +Emit a warning if the current function exceeds the given frame size. Because +this is a compile time check it doesn't need to be a real problem when the program +runs. It is intended to identify functions which most probably cause +a stack overflow. It is useful to be used in an environment with limited stack +size e.g.@: the linux kernel. + +@item -mwarn-dynamicstack +@opindex mwarn-dynamicstack +Emit a warning if the function calls alloca or uses dynamically +sized arrays. This is generally a bad idea with a limited stack size. + +@item -mstack-guard=@var{stack-guard} +@item -mstack-size=@var{stack-size} +@opindex mstack-guard +@opindex mstack-size +These arguments always have to be used in conjunction. If they are present the s390 +back end emits additional instructions in the function prologue which trigger a trap +if the stack size is @var{stack-guard} bytes above the @var{stack-size} +(remember that the stack on s390 grows downward). These options are intended to +be used to help debugging stack overflow problems. The additionally emitted code +causes only little overhead and hence can also be used in production like systems +without greater performance degradation. The given values have to be exact +powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without +exceeding 64k. +In order to be efficient the extra code makes the assumption that the stack starts +at an address aligned to the value given by @var{stack-size}. +@end table + +@node Score Options +@subsection Score Options +@cindex Score Options + +These options are defined for Score implementations: + +@table @gcctabopt +@item -meb +@opindex meb +Compile code for big endian mode. This is the default. + +@item -mel +@opindex mel +Compile code for little endian mode. + +@item -mnhwloop +@opindex mnhwloop +Disable generate bcnz instruction. + +@item -muls +@opindex muls +Enable generate unaligned load and store instruction. + +@item -mmac +@opindex mmac +Enable the use of multiply-accumulate instructions. Disabled by default. + +@item -mscore5 +@opindex mscore5 +Specify the SCORE5 as the target architecture. + +@item -mscore5u +@opindex mscore5u +Specify the SCORE5U of the target architecture. + +@item -mscore7 +@opindex mscore7 +Specify the SCORE7 as the target architecture. This is the default. + +@item -mscore7d +@opindex mscore7d +Specify the SCORE7D as the target architecture. +@end table + +@node SH Options +@subsection SH Options + +These @samp{-m} options are defined for the SH implementations: + +@table @gcctabopt +@item -m1 +@opindex m1 +Generate code for the SH1. + +@item -m2 +@opindex m2 +Generate code for the SH2. + +@item -m2e +Generate code for the SH2e. + +@item -m3 +@opindex m3 +Generate code for the SH3. + +@item -m3e +@opindex m3e +Generate code for the SH3e. + +@item -m4-nofpu +@opindex m4-nofpu +Generate code for the SH4 without a floating-point unit. + +@item -m4-single-only +@opindex m4-single-only +Generate code for the SH4 with a floating-point unit that only +supports single-precision arithmetic. + +@item -m4-single +@opindex m4-single +Generate code for the SH4 assuming the floating-point unit is in +single-precision mode by default. + +@item -m4 +@opindex m4 +Generate code for the SH4. + +@item -m4a-nofpu +@opindex m4a-nofpu +Generate code for the SH4al-dsp, or for a SH4a in such a way that the +floating-point unit is not used. + +@item -m4a-single-only +@opindex m4a-single-only +Generate code for the SH4a, in such a way that no double-precision +floating point operations are used. + +@item -m4a-single +@opindex m4a-single +Generate code for the SH4a assuming the floating-point unit is in +single-precision mode by default. + +@item -m4a +@opindex m4a +Generate code for the SH4a. + +@item -m4al +@opindex m4al +Same as @option{-m4a-nofpu}, except that it implicitly passes +@option{-dsp} to the assembler. GCC doesn't generate any DSP +instructions at the moment. + +@item -mb +@opindex mb +Compile code for the processor in big endian mode. + +@item -ml +@opindex ml +Compile code for the processor in little endian mode. + +@item -mdalign +@opindex mdalign +Align doubles at 64-bit boundaries. Note that this changes the calling +conventions, and thus some functions from the standard C library will +not work unless you recompile it first with @option{-mdalign}. + +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. + +@item -mbigtable +@opindex mbigtable +Use 32-bit offsets in @code{switch} tables. The default is to use +16-bit offsets. + +@item -mfmovd +@opindex mfmovd +Enable the use of the instruction @code{fmovd}. + +@item -mhitachi +@opindex mhitachi +Comply with the calling conventions defined by Renesas. + +@item -mrenesas +@opindex mhitachi +Comply with the calling conventions defined by Renesas. + +@item -mno-renesas +@opindex mhitachi +Comply with the calling conventions defined for GCC before the Renesas +conventions were available. This option is the default for all +targets of the SH toolchain except for @samp{sh-symbianelf}. + +@item -mnomacsave +@opindex mnomacsave +Mark the @code{MAC} register as call-clobbered, even if +@option{-mhitachi} is given. + +@item -mieee +@opindex mieee +Increase IEEE-compliance of floating-point code. +At the moment, this is equivalent to @option{-fno-finite-math-only}. +When generating 16 bit SH opcodes, getting IEEE-conforming results for +comparisons of NANs / infinities incurs extra overhead in every +floating point comparison, therefore the default is set to +@option{-ffinite-math-only}. + +@item -misize +@opindex misize +Dump instruction size and location in the assembly code. + +@item -mpadstruct +@opindex mpadstruct +This option is deprecated. It pads structures to multiple of 4 bytes, +which is incompatible with the SH ABI@. + +@item -mspace +@opindex mspace +@c APPLE LOCAL 4231761 -Oz +Optimize for space instead of speed. Implied by @option{-Os} and @option{-Oz} (APPLE ONLY). + +@item -mprefergot +@opindex mprefergot +When generating position-independent code, emit function calls using +the Global Offset Table instead of the Procedure Linkage Table. + +@item -musermode +@opindex musermode +Generate a library function call to invalidate instruction cache +entries, after fixing up a trampoline. This library function call +doesn't assume it can write to the whole memory address space. This +is the default when the target is @code{sh-*-linux*}. + +@item -multcost=@var{number} +@opindex multcost=@var{number} +Set the cost to assume for a multiply insn. + +@item -mdiv=@var{strategy} +@opindex mdiv=@var{strategy} +Set the division strategy to use for SHmedia code. @var{strategy} must be +one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call, +inv:call2, inv:fp . +"fp" performs the operation in floating point. This has a very high latency, +but needs only a few instructions, so it might be a good choice if +your code has enough easily exploitable ILP to allow the compiler to +schedule the floating point instructions together with other instructions. +Division by zero causes a floating point exception. +"inv" uses integer operations to calculate the inverse of the divisor, +and then multiplies the dividend with the inverse. This strategy allows +cse and hoisting of the inverse calculation. Division by zero calculates +an unspecified result, but does not trap. +"inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities +have been found, or if the entire operation has been hoisted to the same +place, the last stages of the inverse calculation are intertwined with the +final multiply to reduce the overall latency, at the expense of using a few +more instructions, and thus offering fewer scheduling opportunities with +other code. +"call" calls a library function that usually implements the inv:minlat +strategy. +This gives high code density for m5-*media-nofpu compilations. +"call2" uses a different entry point of the same library function, where it +assumes that a pointer to a lookup table has already been set up, which +exposes the pointer load to cse / code hoisting optimizations. +"inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial +code generation, but if the code stays unoptimized, revert to the "call", +"call2", or "fp" strategies, respectively. Note that the +potentially-trapping side effect of division by zero is carried by a +separate instruction, so it is possible that all the integer instructions +are hoisted out, but the marker for the side effect stays where it is. +A recombination to fp operations or a call is not possible in that case. +"inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case +that the inverse calculation was nor separated from the multiply, they speed +up division where the dividend fits into 20 bits (plus sign where applicable), +by inserting a test to skip a number of operations in this case; this test +slows down the case of larger dividends. inv20u assumes the case of a such +a small dividend to be unlikely, and inv20l assumes it to be likely. + +@item -mdivsi3_libfunc=@var{name} +@opindex mdivsi3_libfunc=@var{name} +Set the name of the library function used for 32 bit signed division to +@var{name}. This only affect the name used in the call and inv:call +division strategies, and the compiler will still expect the same +sets of input/output/clobbered registers as if this option was not present. + +@item -madjust-unroll +@opindex madjust-unroll +Throttle unrolling to avoid thrashing target registers. +This option only has an effect if the gcc code base supports the +TARGET_ADJUST_UNROLL_MAX target hook. + +@item -mindexed-addressing +@opindex mindexed-addressing +Enable the use of the indexed addressing mode for SHmedia32/SHcompact. +This is only safe if the hardware and/or OS implement 32 bit wrap-around +semantics for the indexed addressing mode. The architecture allows the +implementation of processors with 64 bit MMU, which the OS could use to +get 32 bit addressing, but since no current hardware implementation supports +this or any other way to make the indexed addressing mode safe to use in +the 32 bit ABI, the default is -mno-indexed-addressing. + +@item -mgettrcost=@var{number} +@opindex mgettrcost=@var{number} +Set the cost assumed for the gettr instruction to @var{number}. +The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise. + +@item -mpt-fixed +@opindex mpt-fixed +Assume pt* instructions won't trap. This will generally generate better +scheduled code, but is unsafe on current hardware. The current architecture +definition says that ptabs and ptrel trap when the target anded with 3 is 3. +This has the unintentional effect of making it unsafe to schedule ptabs / +ptrel before a branch, or hoist it out of a loop. For example, +__do_global_ctors, a part of libgcc that runs constructors at program +startup, calls functions in a list which is delimited by -1. With the +-mpt-fixed option, the ptabs will be done before testing against -1. +That means that all the constructors will be run a bit quicker, but when +the loop comes to the end of the list, the program crashes because ptabs +loads -1 into a target register. Since this option is unsafe for any +hardware implementing the current architecture specification, the default +is -mno-pt-fixed. Unless the user specifies a specific cost with +@option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100}; +this deters register allocation using target registers for storing +ordinary integers. + +@item -minvalid-symbols +@opindex minvalid-symbols +Assume symbols might be invalid. Ordinary function symbols generated by +the compiler will always be valid to load with movi/shori/ptabs or +movi/shori/ptrel, but with assembler and/or linker tricks it is possible +to generate symbols that will cause ptabs / ptrel to trap. +This option is only meaningful when @option{-mno-pt-fixed} is in effect. +It will then prevent cross-basic-block cse, hoisting and most scheduling +of symbol loads. The default is @option{-mno-invalid-symbols}. +@end table + +@node SPARC Options +@subsection SPARC Options +@cindex SPARC options + +These @samp{-m} options are supported on the SPARC: + +@table @gcctabopt +@item -mno-app-regs +@itemx -mapp-regs +@opindex mno-app-regs +@opindex mapp-regs +Specify @option{-mapp-regs} to generate output using the global registers +2 through 4, which the SPARC SVR4 ABI reserves for applications. This +is the default. + +To be fully SVR4 ABI compliant at the cost of some performance loss, +specify @option{-mno-app-regs}. You should compile libraries and system +software with this option. + +@item -mfpu +@itemx -mhard-float +@opindex mfpu +@opindex mhard-float +Generate output containing floating point instructions. This is the +default. + +@item -mno-fpu +@itemx -msoft-float +@opindex mno-fpu +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all SPARC +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. The embedded targets @samp{sparc-*-aout} and +@samp{sparclite-*-*} do provide software floating point support. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mhard-quad-float +@opindex mhard-quad-float +Generate output containing quad-word (long double) floating point +instructions. + +@item -msoft-quad-float +@opindex msoft-quad-float +Generate output containing library calls for quad-word (long double) +floating point instructions. The functions called are those specified +in the SPARC ABI@. This is the default. + +As of this writing, there are no SPARC implementations that have hardware +support for the quad-word floating point instructions. They all invoke +a trap handler for one of these instructions, and then the trap handler +emulates the effect of the instruction. Because of the trap handler overhead, +this is much slower than calling the ABI library routines. Thus the +@option{-msoft-quad-float} option is the default. + +@item -mno-unaligned-doubles +@itemx -munaligned-doubles +@opindex mno-unaligned-doubles +@opindex munaligned-doubles +Assume that doubles have 8 byte alignment. This is the default. + +With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte +alignment only if they are contained in another type, or if they have an +absolute address. Otherwise, it assumes they have 4 byte alignment. +Specifying this option avoids some rare compatibility problems with code +generated by other compilers. It is not the default because it results +in a performance loss, especially for floating point code. + +@item -mno-faster-structs +@itemx -mfaster-structs +@opindex mno-faster-structs +@opindex mfaster-structs +With @option{-mfaster-structs}, the compiler assumes that structures +should have 8 byte alignment. This enables the use of pairs of +@code{ldd} and @code{std} instructions for copies in structure +assignment, in place of twice as many @code{ld} and @code{st} pairs. +However, the use of this changed alignment directly violates the SPARC +ABI@. Thus, it's intended only for use on targets where the developer +acknowledges that their resulting code will not be directly in line with +the rules of the ABI@. + +@item -mimpure-text +@opindex mimpure-text +@option{-mimpure-text}, used in addition to @option{-shared}, tells +the compiler to not pass @option{-z text} to the linker when linking a +shared object. Using this option, you can link position-dependent +code into a shared object. + +@option{-mimpure-text} suppresses the ``relocations remain against +allocatable but non-writable sections'' linker error message. +However, the necessary relocations will trigger copy-on-write, and the +shared object is not actually shared across processes. Instead of +using @option{-mimpure-text}, you should compile all source code with +@option{-fpic} or @option{-fPIC}. + +This option is only available on SunOS and Solaris. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling parameters +for machine type @var{cpu_type}. Supported values for @var{cpu_type} are +@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite}, +@samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x}, +@samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, +@samp{ultrasparc3}, and @samp{niagara}. + +Default instruction scheduling parameters are used for values that select +an architecture and not an implementation. These are @samp{v7}, @samp{v8}, +@samp{sparclite}, @samp{sparclet}, @samp{v9}. + +Here is a list of each supported architecture and their supported +implementations. + +@smallexample + v7: cypress + v8: supersparc, hypersparc + sparclite: f930, f934, sparclite86x + sparclet: tsc701 + v9: ultrasparc, ultrasparc3, niagara +@end smallexample + +By default (unless configured otherwise), GCC generates code for the V7 +variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler +additionally optimizes it for the Cypress CY7C602 chip, as used in the +SPARCStation/SPARCServer 3xx series. This is also appropriate for the older +SPARCStation 1, 2, IPX etc. + +With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC +architecture. The only difference from V7 code is that the compiler emits +the integer multiply and integer divide instructions which exist in SPARC-V8 +but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally +optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and +2000 series. + +With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of +the SPARC architecture. This adds the integer multiply, integer divide step +and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. +With @option{-mcpu=f930}, the compiler additionally optimizes it for the +Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With +@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu +MB86934 chip, which is the more recent SPARClite with FPU@. + +With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of +the SPARC architecture. This adds the integer multiply, multiply/accumulate, +integer divide step and scan (@code{ffs}) instructions which exist in SPARClet +but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally +optimizes it for the TEMIC SPARClet chip. + +With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC +architecture. This adds 64-bit integer and floating-point move instructions, +3 additional floating-point condition code registers and conditional move +instructions. With @option{-mcpu=ultrasparc}, the compiler additionally +optimizes it for the Sun UltraSPARC I/II/IIi chips. With +@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the +Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With +@option{-mcpu=niagara}, the compiler additionally optimizes it for +Sun UltraSPARC T1 chips. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the instruction set or register set that the +option @option{-mcpu=@var{cpu_type}} would. + +The same values for @option{-mcpu=@var{cpu_type}} can be used for +@option{-mtune=@var{cpu_type}}, but the only useful values are those +that select a particular cpu implementation. Those are @samp{cypress}, +@samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934}, +@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, +@samp{ultrasparc3}, and @samp{niagara}. + +@item -mv8plus +@itemx -mno-v8plus +@opindex mv8plus +@opindex mno-v8plus +With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The +difference from the V8 ABI is that the global and out registers are +considered 64-bit wide. This is enabled by default on Solaris in 32-bit +mode for all SPARC-V9 processors. + +@item -mvis +@itemx -mno-vis +@opindex mvis +@opindex mno-vis +With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC +Visual Instruction Set extensions. The default is @option{-mno-vis}. +@end table + +These @samp{-m} options are supported in addition to the above +on SPARC-V9 processors in 64-bit environments: + +@table @gcctabopt +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. It is only +available for a few configurations and most notably not on Solaris and Linux. + +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits. + +@item -mcmodel=medlow +@opindex mcmodel=medlow +Generate code for the Medium/Low code model: 64-bit addresses, programs +must be linked in the low 32 bits of memory. Programs can be statically +or dynamically linked. + +@item -mcmodel=medmid +@opindex mcmodel=medmid +Generate code for the Medium/Middle code model: 64-bit addresses, programs +must be linked in the low 44 bits of memory, the text and data segments must +be less than 2GB in size and the data segment must be located within 2GB of +the text segment. + +@item -mcmodel=medany +@opindex mcmodel=medany +Generate code for the Medium/Anywhere code model: 64-bit addresses, programs +may be linked anywhere in memory, the text and data segments must be less +than 2GB in size and the data segment must be located within 2GB of the +text segment. + +@item -mcmodel=embmedany +@opindex mcmodel=embmedany +Generate code for the Medium/Anywhere code model for embedded systems: +64-bit addresses, the text and data segments must be less than 2GB in +size, both starting anywhere in memory (determined at link time). The +global register %g4 points to the base of the data segment. Programs +are statically linked and PIC is not supported. + +@item -mstack-bias +@itemx -mno-stack-bias +@opindex mstack-bias +@opindex mno-stack-bias +With @option{-mstack-bias}, GCC assumes that the stack pointer, and +frame pointer if present, are offset by @minus{}2047 which must be added back +when making stack frame references. This is the default in 64-bit mode. +Otherwise, assume no such offset is present. +@end table + +These switches are supported in addition to the above on Solaris: + +@table @gcctabopt +@item -threads +@opindex threads +Add support for multithreading using the Solaris threads library. This +option sets flags for both the preprocessor and linker. This option does +not affect the thread safety of object code produced by the compiler or +that of libraries supplied with it. + +@item -pthreads +@opindex pthreads +Add support for multithreading using the POSIX threads library. This +option sets flags for both the preprocessor and linker. This option does +not affect the thread safety of object code produced by the compiler or +that of libraries supplied with it. + +@item -pthread +@opindex pthread +This is a synonym for @option{-pthreads}. +@end table + +@node System V Options +@subsection Options for System V + +These additional options are available on System V Release 4 for +compatibility with other compilers on those systems: + +@table @gcctabopt +@item -G +@opindex G +Create a shared object. +It is recommended that @option{-symbolic} or @option{-shared} be used instead. + +@item -Qy +@opindex Qy +Identify the versions of each tool used by the compiler, in a +@code{.ident} assembler directive in the output. + +@item -Qn +@opindex Qn +Refrain from adding @code{.ident} directives to the output file (this is +the default). + +@item -YP,@var{dirs} +@opindex YP +Search the directories @var{dirs}, and no others, for libraries +specified with @option{-l}. + +@item -Ym,@var{dir} +@opindex Ym +Look in the directory @var{dir} to find the M4 preprocessor. +The assembler uses this option. +@c This is supposed to go with a -Yd for predefined M4 macro files, but +@c the generic assembler that comes with Solaris takes just -Ym. +@end table + +@node TMS320C3x/C4x Options +@subsection TMS320C3x/C4x Options +@cindex TMS320C3x/C4x Options + +These @samp{-m} options are defined for TMS320C3x/C4x implementations: + +@table @gcctabopt + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling +parameters for machine type @var{cpu_type}. Supported values for +@var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and +@samp{c44}. The default is @samp{c40} to generate code for the +TMS320C40. + +@item -mbig-memory +@itemx -mbig +@itemx -msmall-memory +@itemx -msmall +@opindex mbig-memory +@opindex mbig +@opindex msmall-memory +@opindex msmall +Generates code for the big or small memory model. The small memory +model assumed that all data fits into one 64K word page. At run-time +the data page (DP) register must be set to point to the 64K page +containing the .bss and .data program sections. The big memory model is +the default and requires reloading of the DP register for every direct +memory access. + +@item -mbk +@itemx -mno-bk +@opindex mbk +@opindex mno-bk +Allow (disallow) allocation of general integer operands into the block +count register BK@. + +@item -mdb +@itemx -mno-db +@opindex mdb +@opindex mno-db +Enable (disable) generation of code using decrement and branch, +DBcond(D), instructions. This is enabled by default for the C4x. To be +on the safe side, this is disabled for the C3x, since the maximum +iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than +@math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so +that it can utilize the decrement and branch instruction, but will give +up if there is more than one memory reference in the loop. Thus a loop +where the loop counter is decremented can generate slightly more +efficient code, in cases where the RPTB instruction cannot be utilized. + +@item -mdp-isr-reload +@itemx -mparanoid +@opindex mdp-isr-reload +@opindex mparanoid +Force the DP register to be saved on entry to an interrupt service +routine (ISR), reloaded to point to the data section, and restored on +exit from the ISR@. This should not be required unless someone has +violated the small memory model by modifying the DP register, say within +an object library. + +@item -mmpyi +@itemx -mno-mpyi +@opindex mmpyi +@opindex mno-mpyi +For the C3x use the 24-bit MPYI instruction for integer multiplies +instead of a library call to guarantee 32-bit results. Note that if one +of the operands is a constant, then the multiplication will be performed +using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x, +then squaring operations are performed inline instead of a library call. + +@item -mfast-fix +@itemx -mno-fast-fix +@opindex mfast-fix +@opindex mno-fast-fix +The C3x/C4x FIX instruction to convert a floating point value to an +integer value chooses the nearest integer less than or equal to the +floating point value rather than to the nearest integer. Thus if the +floating point number is negative, the result will be incorrectly +truncated an additional code is necessary to detect and correct this +case. This option can be used to disable generation of the additional +code required to correct the result. + +@item -mrptb +@itemx -mno-rptb +@opindex mrptb +@opindex mno-rptb +Enable (disable) generation of repeat block sequences using the RPTB +instruction for zero overhead looping. The RPTB construct is only used +for innermost loops that do not call functions or jump across the loop +boundaries. There is no advantage having nested RPTB loops due to the +overhead required to save and restore the RC, RS, and RE registers. +This is enabled by default with @option{-O2}. + +@item -mrpts=@var{count} +@itemx -mno-rpts +@opindex mrpts +@opindex mno-rpts +Enable (disable) the use of the single instruction repeat instruction +RPTS@. If a repeat block contains a single instruction, and the loop +count can be guaranteed to be less than the value @var{count}, GCC will +emit a RPTS instruction instead of a RPTB@. If no value is specified, +then a RPTS will be emitted even if the loop count cannot be determined +at compile time. Note that the repeated instruction following RPTS does +not have to be reloaded from memory each iteration, thus freeing up the +CPU buses for operands. However, since interrupts are blocked by this +instruction, it is disabled by default. + +@item -mloop-unsigned +@itemx -mno-loop-unsigned +@opindex mloop-unsigned +@opindex mno-loop-unsigned +The maximum iteration count when using RPTS and RPTB (and DB on the C40) +is @math{2^{31} + 1} since these instructions test if the iteration count is +negative to terminate the loop. If the iteration count is unsigned +there is a possibility than the @math{2^{31} + 1} maximum iteration count may be +exceeded. This switch allows an unsigned iteration count. + +@item -mti +@opindex mti +Try to emit an assembler syntax that the TI assembler (asm30) is happy +with. This also enforces compatibility with the API employed by the TI +C3x C compiler. For example, long doubles are passed as structures +rather than in floating point registers. + +@item -mregparm +@itemx -mmemparm +@opindex mregparm +@opindex mmemparm +Generate code that uses registers (stack) for passing arguments to functions. +By default, arguments are passed in registers where possible rather +than by pushing arguments on to the stack. + +@item -mparallel-insns +@itemx -mno-parallel-insns +@opindex mparallel-insns +@opindex mno-parallel-insns +Allow the generation of parallel instructions. This is enabled by +default with @option{-O2}. + +@item -mparallel-mpy +@itemx -mno-parallel-mpy +@opindex mparallel-mpy +@opindex mno-parallel-mpy +Allow the generation of MPY||ADD and MPY||SUB parallel instructions, +provided @option{-mparallel-insns} is also specified. These instructions have +tight register constraints which can pessimize the code generation +of large functions. + +@end table + +@node V850 Options +@subsection V850 Options +@cindex V850 Options + +These @samp{-m} options are defined for V850 implementations: + +@table @gcctabopt +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Treat all calls as being far away (near). If calls are assumed to be +far away, the compiler will always load the functions address up into a +register, and call indirect through the pointer. + +@item -mno-ep +@itemx -mep +@opindex mno-ep +@opindex mep +Do not optimize (do optimize) basic blocks that use the same index +pointer 4 or more times to copy pointer into the @code{ep} register, and +use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} +option is on by default if you optimize. + +@item -mno-prolog-function +@itemx -mprolog-function +@opindex mno-prolog-function +@opindex mprolog-function +Do not use (do use) external functions to save and restore registers +at the prologue and epilogue of a function. The external functions +are slower, but use less code space if more than one function saves +the same number of registers. The @option{-mprolog-function} option +is on by default if you optimize. + +@item -mspace +@opindex mspace +Try to make the code as small as possible. At present, this just turns +on the @option{-mep} and @option{-mprolog-function} options. + +@item -mtda=@var{n} +@opindex mtda +Put static or global variables whose size is @var{n} bytes or less into +the tiny data area that register @code{ep} points to. The tiny data +area can hold up to 256 bytes in total (128 bytes for byte references). + +@item -msda=@var{n} +@opindex msda +Put static or global variables whose size is @var{n} bytes or less into +the small data area that register @code{gp} points to. The small data +area can hold up to 64 kilobytes. + +@item -mzda=@var{n} +@opindex mzda +Put static or global variables whose size is @var{n} bytes or less into +the first 32 kilobytes of memory. + +@item -mv850 +@opindex mv850 +Specify that the target processor is the V850. + +@item -mbig-switch +@opindex mbig-switch +Generate code suitable for big switch tables. Use this option only if +the assembler/linker complain about out of range branches within a switch +table. + +@item -mapp-regs +@opindex mapp-regs +This option will cause r2 and r5 to be used in the code generated by +the compiler. This setting is the default. + +@item -mno-app-regs +@opindex mno-app-regs +This option will cause r2 and r5 to be treated as fixed registers. + +@item -mv850e1 +@opindex mv850e1 +Specify that the target processor is the V850E1. The preprocessor +constants @samp{__v850e1__} and @samp{__v850e__} will be defined if +this option is used. + +@item -mv850e +@opindex mv850e +Specify that the target processor is the V850E@. The preprocessor +constant @samp{__v850e__} will be defined if this option is used. + +If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} +are defined then a default target processor will be chosen and the +relevant @samp{__v850*__} preprocessor constant will be defined. + +The preprocessor constants @samp{__v850} and @samp{__v851__} are always +defined, regardless of which processor variant is the target. + +@item -mdisable-callt +@opindex mdisable-callt +This option will suppress generation of the CALLT instruction for the +v850e and v850e1 flavors of the v850 architecture. The default is +@option{-mno-disable-callt} which allows the CALLT instruction to be used. + +@end table + +@node VAX Options +@subsection VAX Options +@cindex VAX options + +These @samp{-m} options are defined for the VAX: + +@table @gcctabopt +@item -munix +@opindex munix +Do not output certain jump instructions (@code{aobleq} and so on) +that the Unix assembler for the VAX cannot handle across long +ranges. + +@item -mgnu +@opindex mgnu +Do output those jump instructions, on the assumption that you +will assemble with the GNU assembler. + +@item -mg +@opindex mg +Output code for g-format floating point numbers instead of d-format. +@end table + +@node x86-64 Options +@subsection x86-64 Options +@cindex x86-64 options + +These are listed under @xref{i386 and x86-64 Options}. + +@node Xstormy16 Options +@subsection Xstormy16 Options +@cindex Xstormy16 Options + +These options are defined for Xstormy16: + +@table @gcctabopt +@item -msim +@opindex msim +Choose startup files and linker script suitable for the simulator. +@end table + +@node Xtensa Options +@subsection Xtensa Options +@cindex Xtensa Options + +These options are supported for Xtensa targets: + +@table @gcctabopt +@item -mconst16 +@itemx -mno-const16 +@opindex mconst16 +@opindex mno-const16 +Enable or disable use of @code{CONST16} instructions for loading +constant values. The @code{CONST16} instruction is currently not a +standard option from Tensilica. When enabled, @code{CONST16} +instructions are always used in place of the standard @code{L32R} +instructions. The use of @code{CONST16} is enabled by default only if +the @code{L32R} instruction is not available. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Enable or disable use of fused multiply/add and multiply/subtract +instructions in the floating-point option. This has no effect if the +floating-point option is not also enabled. Disabling fused multiply/add +and multiply/subtract instructions forces the compiler to use separate +instructions for the multiply and add/subtract operations. This may be +desirable in some cases where strict IEEE 754-compliant results are +required: the fused multiply add/subtract instructions do not round the +intermediate result, thereby producing results with @emph{more} bits of +precision than specified by the IEEE standard. Disabling fused multiply +add/subtract instructions also ensures that the program output is not +sensitive to the compiler's ability to combine multiply and add/subtract +operations. + +@item -mtext-section-literals +@itemx -mno-text-section-literals +@opindex mtext-section-literals +@opindex mno-text-section-literals +Control the treatment of literal pools. The default is +@option{-mno-text-section-literals}, which places literals in a separate +section in the output file. This allows the literal pool to be placed +in a data RAM/ROM, and it also allows the linker to combine literal +pools from separate object files to remove redundant literals and +improve code size. With @option{-mtext-section-literals}, the literals +are interspersed in the text section in order to keep them as close as +possible to their references. This may be necessary for large assembly +files. + +@item -mtarget-align +@itemx -mno-target-align +@opindex mtarget-align +@opindex mno-target-align +When this option is enabled, GCC instructs the assembler to +automatically align instructions to reduce branch penalties at the +expense of some code density. The assembler attempts to widen density +instructions to align branch targets and the instructions following call +instructions. If there are not enough preceding safe density +instructions to align a target, no widening will be performed. The +default is @option{-mtarget-align}. These options do not affect the +treatment of auto-aligned instructions like @code{LOOP}, which the +assembler will always align, either by widening density instructions or +by inserting no-op instructions. + +@item -mlongcalls +@itemx -mno-longcalls +@opindex mlongcalls +@opindex mno-longcalls +When this option is enabled, GCC instructs the assembler to translate +direct calls to indirect calls unless it can determine that the target +of a direct call is in the range allowed by the call instruction. This +translation typically occurs for calls to functions in other source +files. Specifically, the assembler translates a direct @code{CALL} +instruction into an @code{L32R} followed by a @code{CALLX} instruction. +The default is @option{-mno-longcalls}. This option should be used in +programs where the call target can potentially be out of range. This +option is implemented in the assembler, not the compiler, so the +assembly code generated by GCC will still show direct call +instructions---look at the disassembled object code to see the actual +instructions. Note that the assembler will use an indirect call for +every cross-file call, not just those that really will be out of range. +@end table + +@node zSeries Options +@subsection zSeries Options +@cindex zSeries options + +These are listed under @xref{S/390 and zSeries Options}. +@c APPLE LOCAL prune man page +@end ignore + +@node Code Gen Options +@section Options for Code Generation Conventions +@cindex code generation conventions +@cindex options, code generation +@cindex run-time options + +These machine-independent options control the interface conventions +used in code generation. + +Most of them have both positive and negative forms; the negative form +of @option{-ffoo} would be @option{-fno-foo}. In the table below, only +one of the forms is listed---the one which is not the default. You +can figure out the other form by either removing @samp{no-} or adding +it. + +@table @gcctabopt +@item -fbounds-check +@opindex fbounds-check +For front-ends that support it, generate additional code to check that +indices used to access arrays are within the declared range. This is +currently only supported by the Java and Fortran front-ends, where +this option defaults to true and false respectively. + +@c APPLE LOCAL prune man page 5547358 +@ignore +@item -ftrapv +@opindex ftrapv +This option generates traps for signed overflow on addition, subtraction, +multiplication operations. +@c APPLE LOCAL prune man page 5547358 +@end ignore + +@item -fwrapv +@opindex fwrapv +This option instructs the compiler to assume that signed arithmetic +overflow of addition, subtraction and multiplication wraps around +using twos-complement representation. This flag enables some optimizations +and disables others. This option is enabled by default for the Java +front-end, as required by the Java language specification. + +@item -fexceptions +@opindex fexceptions +Enable exception handling. Generates extra code needed to propagate +exceptions. For some targets, this implies GCC will generate frame +unwind information for all functions, which can produce significant data +size overhead, although it does not affect execution. If you do not +specify this option, GCC will enable it by default for languages like +C++ which normally require exception handling, and disable it for +languages like C that do not normally require it. However, you may need +to enable this option when compiling C code that needs to interoperate +properly with exception handlers written in C++. You may also wish to +disable this option if you are compiling older C++ programs that don't +use exception handling. + +@item -fnon-call-exceptions +@opindex fnon-call-exceptions +Generate code that allows trapping instructions to throw exceptions. +Note that this requires platform-specific runtime support that does +not exist everywhere. Moreover, it only allows @emph{trapping} +instructions to throw exceptions, i.e.@: memory references or floating +point instructions. It does not allow exceptions to be thrown from +arbitrary signal handlers such as @code{SIGALRM}. + +@item -funwind-tables +@opindex funwind-tables +Similar to @option{-fexceptions}, except that it will just generate any needed +static data, but will not affect the generated code in any other way. +You will normally not enable this option; instead, a language processor +that needs this handling would enable it on your behalf. + +@item -fasynchronous-unwind-tables +@opindex fasynchronous-unwind-tables +Generate unwind table in dwarf2 format, if supported by target machine. The +table is exact at each instruction boundary, so it can be used for stack +unwinding from asynchronous events (such as debugger or garbage collector). + +@item -fpcc-struct-return +@opindex fpcc-struct-return +Return ``short'' @code{struct} and @code{union} values in memory like +longer ones, rather than in registers. This convention is less +efficient, but it has the advantage of allowing intercallability between +GCC-compiled files and files compiled with other compilers, particularly +the Portable C Compiler (pcc). + +The precise convention for returning structures in memory depends +on the target configuration macros. + +Short structures and unions are those whose size and alignment match +that of some integer type. + +@strong{Warning:} code compiled with the @option{-fpcc-struct-return} +switch is not binary compatible with code compiled with the +@option{-freg-struct-return} switch. +Use it to conform to a non-default application binary interface. + +@item -freg-struct-return +@opindex freg-struct-return +Return @code{struct} and @code{union} values in registers when possible. +This is more efficient for small structures than +@option{-fpcc-struct-return}. + +If you specify neither @option{-fpcc-struct-return} nor +@option{-freg-struct-return}, GCC defaults to whichever convention is +standard for the target. If there is no standard convention, GCC +defaults to @option{-fpcc-struct-return}, except on targets where GCC is +the principal compiler. In those cases, we can choose the standard, and +we chose the more efficient register return alternative. + +@strong{Warning:} code compiled with the @option{-freg-struct-return} +switch is not binary compatible with code compiled with the +@option{-fpcc-struct-return} switch. +Use it to conform to a non-default application binary interface. + +@item -fshort-enums +@opindex fshort-enums +Allocate to an @code{enum} type only as many bytes as it needs for the +declared range of possible values. Specifically, the @code{enum} type +will be equivalent to the smallest integer type which has enough room. + +@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Use it to conform to a non-default application binary interface. + +@item -fshort-double +@opindex fshort-double +Use the same size for @code{double} as for @code{float}. + +@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Use it to conform to a non-default application binary interface. + +@item -fshort-wchar +@opindex fshort-wchar +Override the underlying type for @samp{wchar_t} to be @samp{short +unsigned int} instead of the default for the target. This option is +useful for building programs to run under WINE@. + +@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Use it to conform to a non-default application binary interface. + +@item -fno-common +@opindex fno-common +In C, allocate even uninitialized global variables in the data section of the +object file, rather than generating them as common blocks. This has the +effect that if the same variable is declared (without @code{extern}) in +two different compilations, you will get an error when you link them. +The only reason this might be useful is if you wish to verify that the +program will work on other systems which always work this way. + +@item -fno-ident +@opindex fno-ident +Ignore the @samp{#ident} directive. + +@item -finhibit-size-directive +@opindex finhibit-size-directive +Don't output a @code{.size} assembler directive, or anything else that +would cause trouble if the function is split in the middle, and the +two halves are placed at locations far apart in memory. This option is +used when compiling @file{crtstuff.c}; you should not need to use it +for anything else. + +@item -fverbose-asm +@opindex fverbose-asm +Put extra commentary information in the generated assembly code to +make it more readable. This option is generally only of use to those +who actually need to read the generated assembly code (perhaps while +debugging the compiler itself). + +@option{-fno-verbose-asm}, the default, causes the +extra information to be omitted and is useful when comparing two assembler +files. + +@item -fpic +@opindex fpic +@cindex global offset table +@cindex PIC +Generate position-independent code (PIC) suitable for use in a shared +library, if supported for the target machine. Such code accesses all +constant addresses through a global offset table (GOT)@. The dynamic +loader resolves the GOT entries when the program starts (the dynamic +loader is not part of GCC; it is part of the operating system). If +the GOT size for the linked executable exceeds a machine-specific +maximum size, you get an error message from the linker indicating that +@option{-fpic} does not work; in that case, recompile with @option{-fPIC} +instead. (These maximums are 8k on the SPARC and 32k +on the m68k and RS/6000. The 386 has no such limit.) + +Position-independent code requires special support, and therefore works +only on certain machines. For the 386, GCC supports PIC for System V +but not for the Sun 386i. Code generated for the IBM RS/6000 is always +position-independent. + +When this flag is set, the macros @code{__pic__} and @code{__PIC__} +are defined to 1. + +@item -fPIC +@opindex fPIC +If supported for the target machine, emit position-independent code, +suitable for dynamic linking and avoiding any limit on the size of the +global offset table. This option makes a difference on the m68k, +PowerPC and SPARC@. + +Position-independent code requires special support, and therefore works +only on certain machines. + +When this flag is set, the macros @code{__pic__} and @code{__PIC__} +are defined to 2. + +@c APPLE LOCAL begin manual +@option{-fPIC} is the default on Darwin and Mac OS X. +@c APPLE LOCAL end manual + +@item -fpie +@itemx -fPIE +@opindex fpie +@opindex fPIE +These options are similar to @option{-fpic} and @option{-fPIC}, but +generated position independent code can be only linked into executables. +Usually these options are used when @option{-pie} GCC option will be +used during linking. + +@item -fno-jump-tables +@opindex fno-jump-tables +Do not use jump tables for switch statements even where it would be +more efficient than other code generation strategies. This option is +of use in conjunction with @option{-fpic} or @option{-fPIC} for +building code which forms part of a dynamic linker and cannot +reference the address of a jump table. On some targets, jump tables +do not require a GOT and this option is not needed. + +@item -ffixed-@var{reg} +@opindex ffixed +Treat the register named @var{reg} as a fixed register; generated code +should never refer to it (except perhaps as a stack pointer, frame +pointer or in some other fixed role). + +@var{reg} must be the name of a register. The register names accepted +are machine-specific and are defined in the @code{REGISTER_NAMES} +macro in the machine description macro file. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-used-@var{reg} +@opindex fcall-used +Treat the register named @var{reg} as an allocable register that is +clobbered by function calls. It may be allocated for temporaries or +variables that do not live across a call. Functions compiled this way +will not save and restore the register @var{reg}. + +It is an error to used this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model will produce disastrous results. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-saved-@var{reg} +@opindex fcall-saved +Treat the register named @var{reg} as an allocable register saved by +functions. It may be allocated even for temporaries or variables that +live across a call. Functions compiled this way will save and restore +the register @var{reg} if they use it. + +It is an error to used this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model will produce disastrous results. + +A different sort of disaster will result from the use of this flag for +a register in which function values may be returned. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fpack-struct[=@var{n}] +@opindex fpack-struct +Without a value specified, pack all structure members together without +holes. When a value is specified (which must be a small power of two), pack +structure members according to this value, representing the maximum +alignment (that is, objects with default alignment requirements larger than +this will be output potentially unaligned at the next fitting location. + +@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Additionally, it makes the code suboptimal. +Use it to conform to a non-default application binary interface. + +@item -finstrument-functions +@opindex finstrument-functions +Generate instrumentation calls for entry and exit to functions. Just +after function entry and just before function exit, the following +profiling functions will be called with the address of the current +function and its call site. (On some platforms, +@code{__builtin_return_address} does not work beyond the current +function, so the call site information may not be available to the +profiling functions otherwise.) + +@smallexample +void __cyg_profile_func_enter (void *this_fn, + void *call_site); +void __cyg_profile_func_exit (void *this_fn, + void *call_site); +@end smallexample + +The first argument is the address of the start of the current function, +which may be looked up exactly in the symbol table. + +This instrumentation is also done for functions expanded inline in other +functions. The profiling calls will indicate where, conceptually, the +inline function is entered and exited. This means that addressable +versions of such functions must be available. If all your uses of a +function are expanded inline, this may mean an additional expansion of +code size. If you use @samp{extern inline} in your C code, an +addressable version of such functions must be provided. (This is +normally the case anyways, but if you get lucky and the optimizer always +expands the functions inline, you might have gotten away without +providing static copies.) + +A function may be given the attribute @code{no_instrument_function}, in +which case this instrumentation will not be done. This can be used, for +example, for the profiling functions listed above, high-priority +interrupt routines, and any functions from which the profiling functions +cannot safely be called (perhaps signal handlers, if the profiling +routines generate output or allocate memory). + +@item -fstack-check +@opindex fstack-check +Generate code to verify that you do not go beyond the boundary of the +stack. You should specify this flag if you are running in an +environment with multiple threads, but only rarely need to specify it in +a single-threaded environment since stack overflow is automatically +detected on nearly all systems if there is only one stack. + +Note that this switch does not actually cause checking to be done; the +operating system must do that. The switch causes generation of code +to ensure that the operating system sees the stack being extended. + +@item -fstack-limit-register=@var{reg} +@itemx -fstack-limit-symbol=@var{sym} +@itemx -fno-stack-limit +@opindex fstack-limit-register +@opindex fstack-limit-symbol +@opindex fno-stack-limit +Generate code to ensure that the stack does not grow beyond a certain value, +either the value of a register or the address of a symbol. If the stack +would grow beyond the value, a signal is raised. For most targets, +the signal is raised before the stack overruns the boundary, so +it is possible to catch the signal without taking special precautions. + +For instance, if the stack starts at absolute address @samp{0x80000000} +and grows downwards, you can use the flags +@option{-fstack-limit-symbol=__stack_limit} and +@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit +of 128KB@. Note that this may only work with the GNU linker. + +@cindex aliasing of parameters +@cindex parameters, aliased +@item -fargument-alias +@itemx -fargument-noalias +@itemx -fargument-noalias-global +@itemx -fargument-noalias-anything +@opindex fargument-alias +@opindex fargument-noalias +@opindex fargument-noalias-global +@opindex fargument-noalias-anything +Specify the possible relationships among parameters and between +parameters and global data. + +@option{-fargument-alias} specifies that arguments (parameters) may +alias each other and may alias global storage.@* +@option{-fargument-noalias} specifies that arguments do not alias +each other, but may alias global storage.@* +@option{-fargument-noalias-global} specifies that arguments do not +alias each other and do not alias global storage. +@option{-fargument-noalias-anything} specifies that arguments do not +alias any other storage. + +Each language will automatically use whatever option is required by +the language standard. You should not need to use these options yourself. + +@item -fleading-underscore +@opindex fleading-underscore +This option and its counterpart, @option{-fno-leading-underscore}, forcibly +change the way C symbols are represented in the object file. One use +is to help link with legacy assembly code. + +@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to +generate code that is not binary compatible with code generated without that +switch. Use it to conform to a non-default application binary interface. +Not all targets provide complete support for this switch. + +@item -ftls-model=@var{model} +Alter the thread-local storage model to be used (@pxref{Thread-Local}). +The @var{model} argument should be one of @code{global-dynamic}, +@code{local-dynamic}, @code{initial-exec} or @code{local-exec}. + +The default without @option{-fpic} is @code{initial-exec}; with +@option{-fpic} the default is @code{global-dynamic}. + +@item -fvisibility=@var{default|internal|hidden|protected} +@opindex fvisibility +Set the default ELF image symbol visibility to the specified option---all +symbols will be marked with this unless overridden within the code. +Using this feature can very substantially improve linking and +load times of shared object libraries, produce more optimized +code, provide near-perfect API export and prevent symbol clashes. +It is @strong{strongly} recommended that you use this in any shared objects +you distribute. + +Despite the nomenclature, @code{default} always means public ie; +available to be linked against from outside the shared object. +@code{protected} and @code{internal} are pretty useless in real-world +usage so the only other commonly used option will be @code{hidden}. +The default if @option{-fvisibility} isn't specified is +@code{default}, i.e., make every +symbol public---this causes the same behavior as previous versions of +GCC@. + +A good explanation of the benefits offered by ensuring ELF +symbols have the correct visibility is given by ``How To Write +Shared Libraries'' by Ulrich Drepper (which can be found at +@w{@uref{http://people.redhat.com/~drepper/}})---however a superior +solution made possible by this option to marking things hidden when +the default is public is to make the default hidden and mark things +public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden} +and @code{__attribute__ ((visibility("default")))} instead of +@code{__declspec(dllexport)} you get almost identical semantics with +identical syntax. This is a great boon to those working with +cross-platform projects. + +For those adding visibility support to existing code, you may find +@samp{#pragma GCC visibility} of use. This works by you enclosing +the declarations you wish to set visibility for with (for example) +@samp{#pragma GCC visibility push(hidden)} and +@samp{#pragma GCC visibility pop}. +Bear in mind that symbol visibility should be viewed @strong{as +part of the API interface contract} and thus all new code should +always specify visibility when it is not the default ie; declarations +only for use within the local DSO should @strong{always} be marked explicitly +as hidden as so to avoid PLT indirection overheads---making this +abundantly clear also aids readability and self-documentation of the code. +Note that due to ISO C++ specification requirements, operator new and +operator delete must always be of default visibility. + +Be aware that headers from outside your project, in particular system +headers and headers from any other library you use, may not be +expecting to be compiled with visibility other than the default. You +may need to explicitly say @samp{#pragma GCC visibility push(default)} +before including any such headers. + +@samp{extern} declarations are not affected by @samp{-fvisibility}, so +a lot of code can be recompiled with @samp{-fvisibility=hidden} with +no modifications. However, this means that calls to @samp{extern} +functions with no explicit visibility will use the PLT, so it is more +effective to use @samp{__attribute ((visibility))} and/or +@samp{#pragma GCC visibility} to tell the compiler which @samp{extern} +declarations should be treated as hidden. + +Note that @samp{-fvisibility} does affect C++ vague linkage +entities. This means that, for instance, an exception class that will +be thrown between DSOs must be explicitly marked with default +visibility so that the @samp{type_info} nodes will be unified between +the DSOs. + +An overview of these techniques, their benefits and how to use them +is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}. + +@end table + +@c man end + +@node Environment Variables +@section Environment Variables Affecting GCC +@cindex environment variables + +@c man begin ENVIRONMENT +This section describes several environment variables that affect how GCC +operates. Some of them work by specifying directories or prefixes to use +when searching for various kinds of files. Some are used to specify other +aspects of the compilation environment. + +Note that you can also specify places to search using options such as +@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These +take precedence over places specified using environment variables, which +in turn take precedence over those specified by the configuration of GCC@. +@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, +GNU Compiler Collection (GCC) Internals}. + +@table @env +@item LANG +@itemx LC_CTYPE +@c @itemx LC_COLLATE +@itemx LC_MESSAGES +@c @itemx LC_MONETARY +@c @itemx LC_NUMERIC +@c @itemx LC_TIME +@itemx LC_ALL +@findex LANG +@findex LC_CTYPE +@c @findex LC_COLLATE +@findex LC_MESSAGES +@c @findex LC_MONETARY +@c @findex LC_NUMERIC +@c @findex LC_TIME +@findex LC_ALL +@cindex locale +These environment variables control the way that GCC uses +localization information that allow GCC to work with different +national conventions. GCC inspects the locale categories +@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do +so. These locale categories can be set to any value supported by your +installation. A typical value is @samp{en_GB.UTF-8} for English in the United +Kingdom encoded in UTF-8. + +The @env{LC_CTYPE} environment variable specifies character +classification. GCC uses it to determine the character boundaries in +a string; this is needed for some multibyte encodings that contain quote +and escape characters that would otherwise be interpreted as a string +end or escape. + +The @env{LC_MESSAGES} environment variable specifies the language to +use in diagnostic messages. + +If the @env{LC_ALL} environment variable is set, it overrides the value +of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} +and @env{LC_MESSAGES} default to the value of the @env{LANG} +environment variable. If none of these variables are set, GCC +defaults to traditional C English behavior. + +@item TMPDIR +@findex TMPDIR +If @env{TMPDIR} is set, it specifies the directory to use for temporary +files. GCC uses temporary files to hold the output of one stage of +compilation which is to be used as input to the next stage: for example, +the output of the preprocessor, which is the input to the compiler +proper. + +@item GCC_EXEC_PREFIX +@findex GCC_EXEC_PREFIX +If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the +names of the subprograms executed by the compiler. No slash is added +when this prefix is combined with the name of a subprogram, but you can +specify a prefix that ends with a slash if you wish. + +If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out +an appropriate prefix to use based on the pathname it was invoked with. + +If GCC cannot find the subprogram using the specified prefix, it +tries looking in the usual places for the subprogram. + +The default value of @env{GCC_EXEC_PREFIX} is +@file{@var{prefix}/lib/gcc/} where @var{prefix} is the value +of @code{prefix} when you ran the @file{configure} script. + +Other prefixes specified with @option{-B} take precedence over this prefix. + +This prefix is also used for finding files such as @file{crt0.o} that are +used for linking. + +In addition, the prefix is used in an unusual way in finding the +directories to search for header files. For each of the standard +directories whose name normally begins with @samp{/usr/local/lib/gcc} +(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries +replacing that beginning with the specified prefix to produce an +alternate directory name. Thus, with @option{-Bfoo/}, GCC will search +@file{foo/bar} where it would normally search @file{/usr/local/lib/bar}. +These alternate directories are searched first; the standard directories +come next. + +@item COMPILER_PATH +@findex COMPILER_PATH +The value of @env{COMPILER_PATH} is a colon-separated list of +directories, much like @env{PATH}. GCC tries the directories thus +specified when searching for subprograms, if it can't find the +subprograms using @env{GCC_EXEC_PREFIX}. + +@item LIBRARY_PATH +@findex LIBRARY_PATH +The value of @env{LIBRARY_PATH} is a colon-separated list of +directories, much like @env{PATH}. When configured as a native compiler, +GCC tries the directories thus specified when searching for special +linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking +using GCC also uses these directories when searching for ordinary +libraries for the @option{-l} option (but directories specified with +@option{-L} come first). + +@item LANG +@findex LANG +@cindex locale definition +This variable is used to pass locale information to the compiler. One way in +which this information is used is to determine the character set to be used +when character literals, string literals and comments are parsed in C and C++. +When the compiler is configured to allow multibyte characters, +the following values for @env{LANG} are recognized: + +@table @samp +@item C-JIS +Recognize JIS characters. +@item C-SJIS +Recognize SJIS characters. +@item C-EUCJP +Recognize EUCJP characters. +@end table + +If @env{LANG} is not defined, or if it has some other value, then the +compiler will use mblen and mbtowc as defined by the default locale to +recognize and translate multibyte characters. + +@c APPLE LOCAL begin ARM 5905142 +@item MACOSX_DEPLOYMENT_TARGET +@itemx IPHONEOS_DEPLOYMENT_TARGET +These variables are used to set the target OS version, as described +for command-line options @option{-mmacosx-version-min} and +@option{-miphoneos-version-min}. Only one OS version can be specified +per architecture, with @env{MACOSX_DEPLOYMENT_TARGET} taking precedence +on non-ARM targets and @env{IPHONEOS_DEPLOYMENT_TARGET} taking +precedence on ARM targets. + +If either command-line option @option{-mmacosx-version-min} or +@option{-miphoneos-version-min} is specified, both of these +environment variables are ignored. +@c APPLE LOCAL end ARM 5905142 +@end table + +@noindent +Some additional environments variables affect the behavior of the +preprocessor. + +@include cppenv.texi + +@c man end + +@node Precompiled Headers +@section Using Precompiled Headers +@cindex precompiled headers +@cindex speed of compilation + +Often large projects have many header files that are included in every +source file. The time the compiler takes to process these header files +over and over again can account for nearly all of the time required to +build the project. To make builds faster, GCC allows users to +`precompile' a header file; then, if builds can use the precompiled +header file they will be much faster. + +To create a precompiled header file, simply compile it as you would any +other file, if necessary using the @option{-x} option to make the driver +treat it as a C or C++ header file. You will probably want to use a +tool like @command{make} to keep the precompiled header up-to-date when +the headers it contains change. + +A precompiled header file will be searched for when @code{#include} is +seen in the compilation. As it searches for the included file +(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the +compiler looks for a precompiled header in each directory just before it +looks for the include file in that directory. The name searched for is +the name specified in the @code{#include} with @samp{.gch} appended. If +the precompiled header file can't be used, it is ignored. + +For instance, if you have @code{#include "all.h"}, and you have +@file{all.h.gch} in the same directory as @file{all.h}, then the +precompiled header file will be used if possible, and the original +header will be used otherwise. + +Alternatively, you might decide to put the precompiled header file in a +directory and use @option{-I} to ensure that directory is searched +before (or instead of) the directory containing the original header. +Then, if you want to check that the precompiled header file is always +used, you can put a file of the same name as the original header in this +directory containing an @code{#error} command. + +This also works with @option{-include}. So yet another way to use +precompiled headers, good for projects not designed with precompiled +header files in mind, is to simply take most of the header files used by +a project, include them from another header file, precompile that header +file, and @option{-include} the precompiled header. If the header files +have guards against multiple inclusion, they will be skipped because +they've already been included (in the precompiled header). + +If you need to precompile the same header file for different +languages, targets, or compiler options, you can instead make a +@emph{directory} named like @file{all.h.gch}, and put each precompiled +header in the directory, perhaps using @option{-o}. It doesn't matter +what you call the files in the directory, every precompiled header in +the directory will be considered. The first precompiled header +encountered in the directory that is valid for this compilation will +be used; they're searched in no particular order. + +There are many other possibilities, limited only by your imagination, +good sense, and the constraints of your build system. + +A precompiled header file can be used only when these conditions apply: + +@itemize +@item +Only one precompiled header can be used in a particular compilation. + +@item +A precompiled header can't be used once the first C token is seen. You +can have preprocessor directives before a precompiled header; you can +even include a precompiled header from inside another header, so long as +there are no C tokens before the @code{#include}. + +@item +The precompiled header file must be produced for the same language as +the current compilation. You can't use a C precompiled header for a C++ +compilation. + +@item +The precompiled header file must have been produced by the same compiler +binary as the current compilation is using. + +@item +Any macros defined before the precompiled header is included must +either be defined in the same way as when the precompiled header was +generated, or must not affect the precompiled header, which usually +means that they don't appear in the precompiled header at all. + +The @option{-D} option is one way to define a macro before a +precompiled header is included; using a @code{#define} can also do it. +There are also some options that define macros implicitly, like +@option{-O} and @option{-Wdeprecated}; the same rule applies to macros +defined this way. + +@item If debugging information is output when using the precompiled +header, using @option{-g} or similar, the same kind of debugging information +must have been output when building the precompiled header. However, +a precompiled header built using @option{-g} can be used in a compilation +when no debugging information is being output. + +@item The same @option{-m} options must generally be used when building +and using the precompiled header. @xref{Submodel Options}, +for any cases where this rule is relaxed. + +@item Each of the following options must be the same when building and using +the precompiled header: + +@gccoptlist{-fexceptions -funit-at-a-time} + +@item +Some other command-line options starting with @option{-f}, +@option{-p}, or @option{-O} must be defined in the same way as when +the precompiled header was generated. At present, it's not clear +which options are safe to change and which are not; the safest choice +is to use exactly the same options when generating and using the +precompiled header. The following are known to be safe: + +@gccoptlist{-fmessage-length= -fpreprocessed +-fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous +-fsched-verbose=<number> -fschedule-insns -fvisibility= +-pedantic-errors} + +@end itemize + +For all of these except the last, the compiler will automatically +ignore the precompiled header if the conditions aren't met. If you +find an option combination that doesn't work and doesn't cause the +precompiled header to be ignored, please consider filing a bug report, +see @ref{Bugs}. + +If you do use differing options when generating and using the +precompiled header, the actual behavior will be a mixture of the +behavior for the options. For instance, if you use @option{-g} to +generate the precompiled header but not when using it, you may or may +not get debugging information for routines in the precompiled header. + +@node Running Protoize +@section Running Protoize + +The program @code{protoize} is an optional part of GCC@. You can use +it to add prototypes to a program, thus converting the program to ISO +C in one respect. The companion program @code{unprotoize} does the +reverse: it removes argument types from any prototypes that are found. + +When you run these programs, you must specify a set of source files as +command line arguments. The conversion programs start out by compiling +these files to see what functions they define. The information gathered +about a file @var{foo} is saved in a file named @file{@var{foo}.X}. + +After scanning comes actual conversion. The specified files are all +eligible to be converted; any files they include (whether sources or +just headers) are eligible as well. + +But not all the eligible files are converted. By default, +@code{protoize} and @code{unprotoize} convert only source and header +files in the current directory. You can specify additional directories +whose files should be converted with the @option{-d @var{directory}} +option. You can also specify particular files to exclude with the +@option{-x @var{file}} option. A file is converted if it is eligible, its +directory name matches one of the specified directory names, and its +name within the directory has not been excluded. + +Basic conversion with @code{protoize} consists of rewriting most +function definitions and function declarations to specify the types of +the arguments. The only ones not rewritten are those for varargs +functions. + +@code{protoize} optionally inserts prototype declarations at the +beginning of the source file, to make them available for any calls that +precede the function's definition. Or it can insert prototype +declarations with block scope in the blocks where undeclared functions +are called. + +Basic conversion with @code{unprotoize} consists of rewriting most +function declarations to remove any argument types, and rewriting +function definitions to the old-style pre-ISO form. + +Both conversion programs print a warning for any function declaration or +definition that they can't convert. You can suppress these warnings +with @option{-q}. + +The output from @code{protoize} or @code{unprotoize} replaces the +original source file. The original file is renamed to a name ending +with @samp{.save} (for DOS, the saved filename ends in @samp{.sav} +without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav} +for DOS) file already exists, then the source file is simply discarded. + +@code{protoize} and @code{unprotoize} both depend on GCC itself to +scan the program and collect information about the functions it uses. +So neither of these programs will work until GCC is installed. + +Here is a table of the options you can use with @code{protoize} and +@code{unprotoize}. Each option works with both programs unless +otherwise stated. + +@table @code +@item -B @var{directory} +Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the +usual directory (normally @file{/usr/local/lib}). This file contains +prototype information about standard system functions. This option +applies only to @code{protoize}. + +@item -c @var{compilation-options} +Use @var{compilation-options} as the options when running @command{gcc} to +produce the @samp{.X} files. The special option @option{-aux-info} is +always passed in addition, to tell @command{gcc} to write a @samp{.X} file. + +Note that the compilation options must be given as a single argument to +@code{protoize} or @code{unprotoize}. If you want to specify several +@command{gcc} options, you must quote the entire set of compilation options +to make them a single word in the shell. + +There are certain @command{gcc} arguments that you cannot use, because they +would produce the wrong kind of output. These include @option{-g}, +@option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in +the @var{compilation-options}, they are ignored. + +@item -C +Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file +systems) instead of @samp{.c}. This is convenient if you are converting +a C program to C++. This option applies only to @code{protoize}. + +@item -g +Add explicit global declarations. This means inserting explicit +declarations at the beginning of each source file for each function +that is called in the file and was not declared. These declarations +precede the first function definition that contains a call to an +undeclared function. This option applies only to @code{protoize}. + +@item -i @var{string} +Indent old-style parameter declarations with the string @var{string}. +This option applies only to @code{protoize}. + +@code{unprotoize} converts prototyped function definitions to old-style +function definitions, where the arguments are declared between the +argument list and the initial @samp{@{}. By default, @code{unprotoize} +uses five spaces as the indentation. If you want to indent with just +one space instead, use @option{-i " "}. + +@item -k +Keep the @samp{.X} files. Normally, they are deleted after conversion +is finished. + +@item -l +Add explicit local declarations. @code{protoize} with @option{-l} inserts +a prototype declaration for each function in each block which calls the +function without any declaration. This option applies only to +@code{protoize}. + +@item -n +Make no real changes. This mode just prints information about the conversions +that would have been done without @option{-n}. + +@item -N +Make no @samp{.save} files. The original files are simply deleted. +Use this option with caution. + +@item -p @var{program} +Use the program @var{program} as the compiler. Normally, the name +@file{gcc} is used. + +@item -q +Work quietly. Most warnings are suppressed. + +@item -v +Print the version number, just like @option{-v} for @command{gcc}. +@end table + +If you need special compiler options to compile one of your program's +source files, then you should generate that file's @samp{.X} file +specially, by running @command{gcc} on that source file with the +appropriate options and the option @option{-aux-info}. Then run +@code{protoize} on the entire set of files. @code{protoize} will use +the existing @samp{.X} file because it is newer than the source file. +For example: + +@smallexample +gcc -Dfoo=bar file1.c -aux-info file1.X +protoize *.c +@end smallexample + +@noindent +You need to include the special files along with the rest in the +@code{protoize} command, even though their @samp{.X} files already +exist, because otherwise they won't get converted. + +@xref{Protoize Caveats}, for more information on how to use +@code{protoize} successfully. |