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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> |