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Porting and Maintenance" /><link rel="prev" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="next" href="abi.html" title="ABI Policy and Guidelines" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Porting to New Hardware or Operating Systems</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="appendix_porting.html">Prev</a> </td><th width="60%" align="center">Appendix B. + Porting and Maintenance + +</th><td width="20%" align="right"> <a accesskey="n" href="abi.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="appendix.porting.internals"></a>Porting to New Hardware or Operating Systems</h2></div></div></div><p> +</p><p>This document explains how to port libstdc++ (the GNU C++ library) to +a new target. +</p><p>In order to make the GNU C++ library (libstdc++) work with a new +target, you must edit some configuration files and provide some new +header files. Unless this is done, libstdc++ will use generic +settings which may not be correct for your target; even if they are +correct, they will likely be inefficient. + </p><p>Before you get started, make sure that you have a working C library on +your target. The C library need not precisely comply with any +particular standard, but should generally conform to the requirements +imposed by the ANSI/ISO standard. + </p><p>In addition, you should try to verify that the C++ compiler generally +works. It is difficult to test the C++ compiler without a working +library, but you should at least try some minimal test cases. + </p><p>(Note that what we think of as a "target," the library refers to as +a "host." The comment at the top of <code class="code">configure.ac</code> explains why.) + </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.os"></a>Operating System</h3></div></div></div><p>If you are porting to a new operating system (as opposed to a new chip +using an existing operating system), you will need to create a new +directory in the <code class="code">config/os</code> hierarchy. For example, the IRIX +configuration files are all in <code class="code">config/os/irix</code>. There is no set +way to organize the OS configuration directory. For example, +<code class="code">config/os/solaris/solaris-2.6</code> and +<code class="code">config/os/solaris/solaris-2.7</code> are used as configuration +directories for these two versions of Solaris. On the other hand, both +Solaris 2.7 and Solaris 2.8 use the <code class="code">config/os/solaris/solaris-2.7</code> +directory. The important information is that there needs to be a +directory under <code class="code">config/os</code> to store the files for your operating +system. +</p><p>You might have to change the <code class="code">configure.host</code> file to ensure that +your new directory is activated. Look for the switch statement that sets +<code class="code">os_include_dir</code>, and add a pattern to handle your operating system +if the default will not suffice. The switch statement switches on only +the OS portion of the standard target triplet; e.g., the <code class="code">solaris2.8</code> +in <code class="code">sparc-sun-solaris2.8</code>. If the new directory is named after the +OS portion of the triplet (the default), then nothing needs to be changed. + </p><p>The first file to create in this directory, should be called +<code class="code">os_defines.h</code>. This file contains basic macro definitions +that are required to allow the C++ library to work with your C library. + </p><p>Several libstdc++ source files unconditionally define the macro +<code class="code">_POSIX_SOURCE</code>. On many systems, defining this macro causes +large portions of the C library header files to be eliminated +at preprocessing time. Therefore, you may have to <code class="code">#undef</code> this +macro, or define other macros (like <code class="code">_LARGEFILE_SOURCE</code> or +<code class="code">__EXTENSIONS__</code>). You won't know what macros to define or +undefine at this point; you'll have to try compiling the library and +seeing what goes wrong. If you see errors about calling functions +that have not been declared, look in your C library headers to see if +the functions are declared there, and then figure out what macros you +need to define. You will need to add them to the +<code class="code">CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your +target. It will not work to simply define these macros in +<code class="code">os_defines.h</code>. + </p><p>At this time, there are a few libstdc++-specific macros which may be +defined: + </p><p><code class="code">_GLIBCXX_USE_C99_CHECK</code> may be defined to 1 to check C99 +function declarations (which are not covered by specialization below) +found in system headers against versions found in the library headers +derived from the standard. + </p><p><code class="code">_GLIBCXX_USE_C99_DYNAMIC</code> may be defined to an expression that +yields 0 if and only if the system headers are exposing proper support +for C99 functions (which are not covered by specialization below). If +defined, it must be 0 while bootstrapping the compiler/rebuilding the +library. + </p><p><code class="code">_GLIBCXX_USE_C99_LONG_LONG_CHECK</code> may be defined to 1 to check +the set of C99 long long function declarations found in system headers +against versions found in the library headers derived from the +standard. + + </p><p><code class="code">_GLIBCXX_USE_C99_LONG_LONG_DYNAMIC</code> may be defined to an +expression that yields 0 if and only if the system headers are +exposing proper support for the set of C99 long long functions. If +defined, it must be 0 while bootstrapping the compiler/rebuilding the +library. + </p><p><code class="code">_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC</code> may be defined to an +expression that yields 0 if and only if the system headers +are exposing proper support for the related set of macros. If defined, +it must be 0 while bootstrapping the compiler/rebuilding the library. + </p><p><code class="code">_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_CHECK</code> may be defined +to 1 to check the related set of function declarations found in system +headers against versions found in the library headers derived from +the standard. + </p><p><code class="code">_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_DYNAMIC</code> may be defined +to an expression that yields 0 if and only if the system headers +are exposing proper support for the related set of functions. If defined, +it must be 0 while bootstrapping the compiler/rebuilding the library. + </p><p>Finally, you should bracket the entire file in an include-guard, like +this: + </p><pre class="programlisting"> + +#ifndef _GLIBCXX_OS_DEFINES +#define _GLIBCXX_OS_DEFINES +... +#endif +</pre><p>We recommend copying an existing <code class="code">os_defines.h</code> to use as a +starting point. + </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.cpu"></a>CPU</h3></div></div></div><p>If you are porting to a new chip (as opposed to a new operating system +running on an existing chip), you will need to create a new directory in the +<code class="code">config/cpu</code> hierarchy. Much like the <a class="link" href="internals.html#internals.os" title="Operating System">Operating system</a> setup, +there are no strict rules on how to organize the CPU configuration +directory, but careful naming choices will allow the configury to find your +setup files without explicit help. +</p><p>We recommend that for a target triplet <code class="code"><CPU>-<vendor>-<OS></code>, you +name your configuration directory <code class="code">config/cpu/<CPU></code>. If you do this, +the configury will find the directory by itself. Otherwise you will need to +edit the <code class="code">configure.host</code> file and, in the switch statement that sets +<code class="code">cpu_include_dir</code>, add a pattern to handle your chip. + </p><p>Note that some chip families share a single configuration directory, for +example, <code class="code">alpha</code>, <code class="code">alphaev5</code>, and <code class="code">alphaev6</code> all use the +<code class="code">config/cpu/alpha</code> directory, and there is an entry in the +<code class="code">configure.host</code> switch statement to handle this. + </p><p>The <code class="code">cpu_include_dir</code> sets default locations for the files controlling +<a class="link" href="internals.html#internals.thread_safety" title="Thread Safety">Thread safety</a> and <a class="link" href="internals.html#internals.numeric_limits" title="Numeric Limits">Numeric limits</a>, if the defaults are not +appropriate for your chip. + </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.char_types"></a>Character Types</h3></div></div></div><p>The library requires that you provide three header files to implement +character classification, analogous to that provided by the C libraries +<code class="code"><ctype.h></code> header. You can model these on the files provided in +<code class="code">config/os/generic</code>. However, these files will almost +certainly need some modification. +</p><p>The first file to write is <code class="code">ctype_base.h</code>. This file provides +some very basic information about character classification. The libstdc++ +library assumes that your C library implements <code class="code"><ctype.h></code> by using +a table (indexed by character code) containing integers, where each of +these integers is a bit-mask indicating whether the character is +upper-case, lower-case, alphabetic, etc. The <code class="code">ctype_base.h</code> +file gives the type of the integer, and the values of the various bit +masks. You will have to peer at your own <code class="code"><ctype.h></code> to figure out +how to define the values required by this file. + </p><p>The <code class="code">ctype_base.h</code> header file does not need include guards. +It should contain a single <code class="code">struct</code> definition called +<code class="code">ctype_base</code>. This <code class="code">struct</code> should contain two type +declarations, and one enumeration declaration, like this example, taken +from the IRIX configuration: + </p><pre class="programlisting"> + struct ctype_base + { + typedef unsigned int mask; + typedef int* __to_type; + + enum + { + space = _ISspace, + print = _ISprint, + cntrl = _IScntrl, + upper = _ISupper, + lower = _ISlower, + alpha = _ISalpha, + digit = _ISdigit, + punct = _ISpunct, + xdigit = _ISxdigit, + alnum = _ISalnum, + graph = _ISgraph + }; + }; +</pre><p>The <code class="code">mask</code> type is the type of the elements in the table. If your +C library uses a table to map lower-case numbers to upper-case numbers, +and vice versa, you should define <code class="code">__to_type</code> to be the type of the +elements in that table. If you don't mind taking a minor performance +penalty, or if your library doesn't implement <code class="code">toupper</code> and +<code class="code">tolower</code> in this way, you can pick any pointer-to-integer type, +but you must still define the type. +</p><p>The enumeration should give definitions for all the values in the above +example, using the values from your native <code class="code"><ctype.h></code>. They can +be given symbolically (as above), or numerically, if you prefer. You do +not have to include <code class="code"><ctype.h></code> in this header; it will always be +included before <code class="code">ctype_base.h</code> is included. + </p><p>The next file to write is <code class="code">ctype_noninline.h</code>, which also does +not require include guards. This file defines a few member functions +that will be included in <code class="code">include/bits/locale_facets.h</code>. The first +function that must be written is the <code class="code">ctype<char>::ctype</code> +constructor. Here is the IRIX example: + </p><pre class="programlisting"> +ctype<char>::ctype(const mask* __table = 0, bool __del = false, + size_t __refs = 0) + : _Ctype_nois<char>(__refs), _M_del(__table != 0 && __del), + _M_toupper(NULL), + _M_tolower(NULL), + _M_ctable(NULL), + _M_table(!__table + ? (const mask*) (__libc_attr._ctype_tbl->_class + 1) + : __table) + { } +</pre><p>There are two parts of this that you might choose to alter. The first, +and most important, is the line involving <code class="code">__libc_attr</code>. That is +IRIX system-dependent code that gets the base of the table mapping +character codes to attributes. You need to substitute code that obtains +the address of this table on your system. If you want to use your +operating system's tables to map upper-case letters to lower-case, and +vice versa, you should initialize <code class="code">_M_toupper</code> and +<code class="code">_M_tolower</code> with those tables, in similar fashion. +</p><p>Now, you have to write two functions to convert from upper-case to +lower-case, and vice versa. Here are the IRIX versions: + </p><pre class="programlisting"> + char + ctype<char>::do_toupper(char __c) const + { return _toupper(__c); } + + char + ctype<char>::do_tolower(char __c) const + { return _tolower(__c); } +</pre><p>Your C library provides equivalents to IRIX's <code class="code">_toupper</code> and +<code class="code">_tolower</code>. If you initialized <code class="code">_M_toupper</code> and +<code class="code">_M_tolower</code> above, then you could use those tables instead. +</p><p>Finally, you have to provide two utility functions that convert strings +of characters. The versions provided here will always work - but you +could use specialized routines for greater performance if you have +machinery to do that on your system: + </p><pre class="programlisting"> + const char* + ctype<char>::do_toupper(char* __low, const char* __high) const + { + while (__low < __high) + { + *__low = do_toupper(*__low); + ++__low; + } + return __high; + } + + const char* + ctype<char>::do_tolower(char* __low, const char* __high) const + { + while (__low < __high) + { + *__low = do_tolower(*__low); + ++__low; + } + return __high; + } +</pre><p>You must also provide the <code class="code">ctype_inline.h</code> file, which +contains a few more functions. On most systems, you can just copy +<code class="code">config/os/generic/ctype_inline.h</code> and use it on your system. + </p><p>In detail, the functions provided test characters for particular +properties; they are analogous to the functions like <code class="code">isalpha</code> and +<code class="code">islower</code> provided by the C library. + </p><p>The first function is implemented like this on IRIX: + </p><pre class="programlisting"> + bool + ctype<char>:: + is(mask __m, char __c) const throw() + { return (_M_table)[(unsigned char)(__c)] & __m; } +</pre><p>The <code class="code">_M_table</code> is the table passed in above, in the constructor. +This is the table that contains the bitmasks for each character. The +implementation here should work on all systems. +</p><p>The next function is: + </p><pre class="programlisting"> + const char* + ctype<char>:: + is(const char* __low, const char* __high, mask* __vec) const throw() + { + while (__low < __high) + *__vec++ = (_M_table)[(unsigned char)(*__low++)]; + return __high; + } +</pre><p>This function is similar; it copies the masks for all the characters +from <code class="code">__low</code> up until <code class="code">__high</code> into the vector given by +<code class="code">__vec</code>. +</p><p>The last two functions again are entirely generic: + </p><pre class="programlisting"> + const char* + ctype<char>:: + scan_is(mask __m, const char* __low, const char* __high) const throw() + { + while (__low < __high && !this->is(__m, *__low)) + ++__low; + return __low; + } + + const char* + ctype<char>:: + scan_not(mask __m, const char* __low, const char* __high) const throw() + { + while (__low < __high && this->is(__m, *__low)) + ++__low; + return __low; + } +</pre></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.thread_safety"></a>Thread Safety</h3></div></div></div><p>The C++ library string functionality requires a couple of atomic +operations to provide thread-safety. If you don't take any special +action, the library will use stub versions of these functions that are +not thread-safe. They will work fine, unless your applications are +multi-threaded. +</p><p>If you want to provide custom, safe, versions of these functions, there +are two distinct approaches. One is to provide a version for your CPU, +using assembly language constructs. The other is to use the +thread-safety primitives in your operating system. In either case, you +make a file called <code class="code">atomicity.h</code>, and the variable +<code class="code">ATOMICITYH</code> must point to this file. + </p><p>If you are using the assembly-language approach, put this code in +<code class="code">config/cpu/<chip>/atomicity.h</code>, where chip is the name of +your processor (see <a class="link" href="internals.html#internals.cpu" title="CPU">CPU</a>). No additional changes are necessary to +locate the file in this case; <code class="code">ATOMICITYH</code> will be set by default. + </p><p>If you are using the operating system thread-safety primitives approach, +you can also put this code in the same CPU directory, in which case no more +work is needed to locate the file. For examples of this approach, +see the <code class="code">atomicity.h</code> file for IRIX or IA64. + </p><p>Alternatively, if the primitives are more closely related to the OS +than they are to the CPU, you can put the <code class="code">atomicity.h</code> file in +the <a class="link" href="internals.html#internals.os" title="Operating System">Operating system</a> directory instead. In this case, you must +edit <code class="code">configure.host</code>, and in the switch statement that handles +operating systems, override the <code class="code">ATOMICITYH</code> variable to point to +the appropriate <code class="code">os_include_dir</code>. For examples of this approach, +see the <code class="code">atomicity.h</code> file for AIX. + </p><p>With those bits out of the way, you have to actually write +<code class="code">atomicity.h</code> itself. This file should be wrapped in an +include guard named <code class="code">_GLIBCXX_ATOMICITY_H</code>. It should define one +type, and two functions. + </p><p>The type is <code class="code">_Atomic_word</code>. Here is the version used on IRIX: + </p><pre class="programlisting"> +typedef long _Atomic_word; +</pre><p>This type must be a signed integral type supporting atomic operations. +If you're using the OS approach, use the same type used by your system's +primitives. Otherwise, use the type for which your CPU provides atomic +primitives. +</p><p>Then, you must provide two functions. The bodies of these functions +must be equivalent to those provided here, but using atomic operations: + </p><pre class="programlisting"> + static inline _Atomic_word + __attribute__ ((__unused__)) + __exchange_and_add (_Atomic_word* __mem, int __val) + { + _Atomic_word __result = *__mem; + *__mem += __val; + return __result; + } + + static inline void + __attribute__ ((__unused__)) + __atomic_add (_Atomic_word* __mem, int __val) + { + *__mem += __val; + } +</pre></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.numeric_limits"></a>Numeric Limits</h3></div></div></div><p>The C++ library requires information about the fundamental data types, +such as the minimum and maximum representable values of each type. +You can define each of these values individually, but it is usually +easiest just to indicate how many bits are used in each of the data +types and let the library do the rest. For information about the +macros to define, see the top of <code class="code">include/bits/std_limits.h</code>. +</p><p>If you need to define any macros, you can do so in <code class="code">os_defines.h</code>. +However, if all operating systems for your CPU are likely to use the +same values, you can provide a CPU-specific file instead so that you +do not have to provide the same definitions for each operating system. +To take that approach, create a new file called <code class="code">cpu_limits.h</code> in +your CPU configuration directory (see <a class="link" href="internals.html#internals.cpu" title="CPU">CPU</a>). + </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="internals.libtool"></a>Libtool</h3></div></div></div><p>The C++ library is compiled, archived and linked with libtool. +Explaining the full workings of libtool is beyond the scope of this +document, but there are a few, particular bits that are necessary for +porting. +</p><p>Some parts of the libstdc++ library are compiled with the libtool +<code class="code">--tags CXX</code> option (the C++ definitions for libtool). Therefore, +<code class="code">ltcf-cxx.sh</code> in the top-level directory needs to have the correct +logic to compile and archive objects equivalent to the C version of libtool, +<code class="code">ltcf-c.sh</code>. Some libtool targets have definitions for C but not +for C++, or C++ definitions which have not been kept up to date. + </p><p>The C++ run-time library contains initialization code that needs to be +run as the library is loaded. Often, that requires linking in special +object files when the C++ library is built as a shared library, or +taking other system-specific actions. + </p><p>The libstdc++ library is linked with the C version of libtool, even +though it is a C++ library. Therefore, the C version of libtool needs to +ensure that the run-time library initializers are run. The usual way to +do this is to build the library using <code class="code">gcc -shared</code>. + </p><p>If you need to change how the library is linked, look at +<code class="code">ltcf-c.sh</code> in the top-level directory. Find the switch statement +that sets <code class="code">archive_cmds</code>. Here, adjust the setting for your +operating system. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="appendix_porting.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="abi.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Appendix B. + Porting and Maintenance + + </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> ABI Policy and Guidelines</td></tr></table></div></body></html> |