mirror of git://gcc.gnu.org/git/gcc.git
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367 lines
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Porting to New Hardware or Operating Systems</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, internals" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="prev" href="documentation_hacking.html" title="Writing and Generating Documentation" /><link rel="next" href="test.html" title="Test" /></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="documentation_hacking.html">Prev</a> </td><th width="60%" align="center">Appendix B.
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Porting and Maintenance
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</th><td width="20%" align="right"> <a accesskey="n" href="test.html">Next</a></td></tr></table><hr /></div><div class="section"><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>
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</p><p>This document explains how to port libstdc++ (the GNU C++ library) to
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a new target.
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</p><p>In order to make the GNU C++ library (libstdc++) work with a new
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target, you must edit some configuration files and provide some new
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header files. Unless this is done, libstdc++ will use generic
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settings which may not be correct for your target; even if they are
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correct, they will likely be inefficient.
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</p><p>Before you get started, make sure that you have a working C library on
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your target. The C library need not precisely comply with any
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particular standard, but should generally conform to the requirements
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imposed by the ANSI/ISO standard.
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</p><p>In addition, you should try to verify that the C++ compiler generally
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works. It is difficult to test the C++ compiler without a working
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library, but you should at least try some minimal test cases.
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</p><p>(Note that what we think of as a "target," the library refers to as
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a "host." The comment at the top of <code class="code">configure.ac</code> explains why.)
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</p><div class="section"><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
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using an existing operating system), you will need to create a new
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directory in the <code class="code">config/os</code> hierarchy. For example, the IRIX
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configuration files are all in <code class="code">config/os/irix</code>. There is no set
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way to organize the OS configuration directory. For example,
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<code class="code">config/os/solaris/solaris-2.6</code> and
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<code class="code">config/os/solaris/solaris-2.7</code> are used as configuration
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||
directories for these two versions of Solaris. On the other hand, both
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Solaris 2.7 and Solaris 2.8 use the <code class="code">config/os/solaris/solaris-2.7</code>
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directory. The important information is that there needs to be a
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directory under <code class="code">config/os</code> to store the files for your operating
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system.
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</p><p>You might have to change the <code class="code">configure.host</code> file to ensure that
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your new directory is activated. Look for the switch statement that sets
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<code class="code">os_include_dir</code>, and add a pattern to handle your operating system
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if the default will not suffice. The switch statement switches on only
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the OS portion of the standard target triplet; e.g., the <code class="code">solaris2.8</code>
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in <code class="code">sparc-sun-solaris2.8</code>. If the new directory is named after the
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OS portion of the triplet (the default), then nothing needs to be changed.
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</p><p>The first file to create in this directory, should be called
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<code class="code">os_defines.h</code>. This file contains basic macro definitions
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that are required to allow the C++ library to work with your C library.
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</p><p>Several libstdc++ source files unconditionally define the macro
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<code class="code">_POSIX_SOURCE</code>. On many systems, defining this macro causes
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large portions of the C library header files to be eliminated
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at preprocessing time. Therefore, you may have to <code class="code">#undef</code> this
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macro, or define other macros (like <code class="code">_LARGEFILE_SOURCE</code> or
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<code class="code">__EXTENSIONS__</code>). You won't know what macros to define or
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undefine at this point; you'll have to try compiling the library and
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seeing what goes wrong. If you see errors about calling functions
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that have not been declared, look in your C library headers to see if
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the functions are declared there, and then figure out what macros you
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need to define. You will need to add them to the
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<code class="code">CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your
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target. It will not work to simply define these macros in
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<code class="code">os_defines.h</code>.
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</p><p>At this time, there are a few libstdc++-specific macros which may be
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defined:
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</p><p><code class="code">_GLIBCXX_USE_C99_CHECK</code> may be defined to 1 to check C99
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function declarations (which are not covered by specialization below)
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found in system headers against versions found in the library headers
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derived from the standard.
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</p><p><code class="code">_GLIBCXX_USE_C99_DYNAMIC</code> may be defined to an expression that
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yields 0 if and only if the system headers are exposing proper support
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for C99 functions (which are not covered by specialization below). If
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defined, it must be 0 while bootstrapping the compiler/rebuilding the
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library.
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</p><p><code class="code">_GLIBCXX_USE_C99_LONG_LONG_CHECK</code> may be defined to 1 to check
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the set of C99 long long function declarations found in system headers
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against versions found in the library headers derived from the
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standard.
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</p><p><code class="code">_GLIBCXX_USE_C99_LONG_LONG_DYNAMIC</code> may be defined to an
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expression that yields 0 if and only if the system headers are
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exposing proper support for the set of C99 long long functions. If
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defined, it must be 0 while bootstrapping the compiler/rebuilding the
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library.
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</p><p><code class="code">_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC</code> may be defined to an
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expression that yields 0 if and only if the system headers
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are exposing proper support for the related set of macros. If defined,
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||
it must be 0 while bootstrapping the compiler/rebuilding the library.
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||
</p><p><code class="code">_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_CHECK</code> may be defined
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to 1 to check the related set of function declarations found in system
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headers against versions found in the library headers derived from
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the standard.
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</p><p><code class="code">_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_DYNAMIC</code> may be defined
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to an expression that yields 0 if and only if the system headers
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are exposing proper support for the related set of functions. If defined,
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it must be 0 while bootstrapping the compiler/rebuilding the library.
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</p><p>Finally, you should bracket the entire file in an include-guard, like
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this:
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</p><pre class="programlisting">
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#ifndef _GLIBCXX_OS_DEFINES
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#define _GLIBCXX_OS_DEFINES
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...
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#endif
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</pre><p>We recommend copying an existing <code class="code">os_defines.h</code> to use as a
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starting point.
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</p></div><div class="section"><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
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running on an existing chip), you will need to create a new directory in the
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<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,
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there are no strict rules on how to organize the CPU configuration
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directory, but careful naming choices will allow the configury to find your
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setup files without explicit help.
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</p><p>We recommend that for a target triplet <code class="code"><CPU>-<vendor>-<OS></code>, you
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name your configuration directory <code class="code">config/cpu/<CPU></code>. If you do this,
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the configury will find the directory by itself. Otherwise you will need to
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edit the <code class="code">configure.host</code> file and, in the switch statement that sets
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<code class="code">cpu_include_dir</code>, add a pattern to handle your chip.
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</p><p>Note that some chip families share a single configuration directory, for
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example, <code class="code">alpha</code>, <code class="code">alphaev5</code>, and <code class="code">alphaev6</code> all use the
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<code class="code">config/cpu/alpha</code> directory, and there is an entry in the
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<code class="code">configure.host</code> switch statement to handle this.
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</p><p>The <code class="code">cpu_include_dir</code> sets default locations for the files controlling
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<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
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appropriate for your chip.
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</p></div><div class="section"><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
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character classification, analogous to that provided by the C libraries
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<code class="code"><ctype.h></code> header. You can model these on the files provided in
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<code class="code">config/os/generic</code>. However, these files will almost
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certainly need some modification.
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</p><p>The first file to write is <code class="code">ctype_base.h</code>. This file provides
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some very basic information about character classification. The libstdc++
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library assumes that your C library implements <code class="code"><ctype.h></code> by using
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a table (indexed by character code) containing integers, where each of
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these integers is a bit-mask indicating whether the character is
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upper-case, lower-case, alphabetic, etc. The <code class="code">ctype_base.h</code>
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file gives the type of the integer, and the values of the various bit
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masks. You will have to peer at your own <code class="code"><ctype.h></code> to figure out
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how to define the values required by this file.
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</p><p>The <code class="code">ctype_base.h</code> header file does not need include guards.
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It should contain a single <code class="code">struct</code> definition called
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<code class="code">ctype_base</code>. This <code class="code">struct</code> should contain two type
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declarations, and one enumeration declaration, like this example, taken
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from the IRIX configuration:
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</p><pre class="programlisting">
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struct ctype_base
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{
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typedef unsigned int mask;
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typedef int* __to_type;
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enum
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{
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space = _ISspace,
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print = _ISprint,
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cntrl = _IScntrl,
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upper = _ISupper,
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lower = _ISlower,
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alpha = _ISalpha,
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digit = _ISdigit,
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punct = _ISpunct,
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xdigit = _ISxdigit,
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alnum = _ISalnum,
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graph = _ISgraph
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};
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};
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</pre><p>The <code class="code">mask</code> type is the type of the elements in the table. If your
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C library uses a table to map lower-case numbers to upper-case numbers,
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and vice versa, you should define <code class="code">__to_type</code> to be the type of the
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elements in that table. If you don't mind taking a minor performance
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penalty, or if your library doesn't implement <code class="code">toupper</code> and
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<code class="code">tolower</code> in this way, you can pick any pointer-to-integer type,
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but you must still define the type.
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</p><p>The enumeration should give definitions for all the values in the above
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example, using the values from your native <code class="code"><ctype.h></code>. They can
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be given symbolically (as above), or numerically, if you prefer. You do
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not have to include <code class="code"><ctype.h></code> in this header; it will always be
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included before <code class="code">ctype_base.h</code> is included.
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</p><p>The next file to write is <code class="code">ctype_configure_char.cc</code>.
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The first function that must be written is the <code class="code">ctype<char>::ctype</code> constructor. Here is the IRIX example:
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</p><pre class="programlisting">
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ctype<char>::ctype(const mask* __table = 0, bool __del = false,
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size_t __refs = 0)
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: _Ctype_nois<char>(__refs), _M_del(__table != 0 && __del),
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_M_toupper(NULL),
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_M_tolower(NULL),
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_M_ctable(NULL),
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_M_table(!__table
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? (const mask*) (__libc_attr._ctype_tbl->_class + 1)
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: __table)
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{ }
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</pre><p>There are two parts of this that you might choose to alter. The first,
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and most important, is the line involving <code class="code">__libc_attr</code>. That is
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IRIX system-dependent code that gets the base of the table mapping
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character codes to attributes. You need to substitute code that obtains
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the address of this table on your system. If you want to use your
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operating system's tables to map upper-case letters to lower-case, and
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||
vice versa, you should initialize <code class="code">_M_toupper</code> and
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<code class="code">_M_tolower</code> with those tables, in similar fashion.
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</p><p>Now, you have to write two functions to convert from upper-case to
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lower-case, and vice versa. Here are the IRIX versions:
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</p><pre class="programlisting">
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char
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ctype<char>::do_toupper(char __c) const
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{ return _toupper(__c); }
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char
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ctype<char>::do_tolower(char __c) const
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{ return _tolower(__c); }
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</pre><p>Your C library provides equivalents to IRIX's <code class="code">_toupper</code> and
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<code class="code">_tolower</code>. If you initialized <code class="code">_M_toupper</code> and
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<code class="code">_M_tolower</code> above, then you could use those tables instead.
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</p><p>Finally, you have to provide two utility functions that convert strings
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of characters. The versions provided here will always work - but you
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could use specialized routines for greater performance if you have
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machinery to do that on your system:
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</p><pre class="programlisting">
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const char*
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ctype<char>::do_toupper(char* __low, const char* __high) const
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{
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while (__low < __high)
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{
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*__low = do_toupper(*__low);
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++__low;
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}
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return __high;
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}
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const char*
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ctype<char>::do_tolower(char* __low, const char* __high) const
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{
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while (__low < __high)
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{
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*__low = do_tolower(*__low);
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++__low;
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}
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return __high;
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}
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</pre><p>You must also provide the <code class="code">ctype_inline.h</code> file, which
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contains a few more functions. On most systems, you can just copy
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<code class="code">config/os/generic/ctype_inline.h</code> and use it on your system.
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||
</p><p>In detail, the functions provided test characters for particular
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properties; they are analogous to the functions like <code class="code">isalpha</code> and
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<code class="code">islower</code> provided by the C library.
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||
</p><p>The first function is implemented like this on IRIX:
|
||
</p><pre class="programlisting">
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||
bool
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ctype<char>::
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is(mask __m, char __c) const throw()
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{ return (_M_table)[(unsigned char)(__c)] & __m; }
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</pre><p>The <code class="code">_M_table</code> is the table passed in above, in the constructor.
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This is the table that contains the bitmasks for each character. The
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||
implementation here should work on all systems.
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</p><p>The next function is:
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</p><pre class="programlisting">
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const char*
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ctype<char>::
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||
is(const char* __low, const char* __high, mask* __vec) const throw()
|
||
{
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while (__low < __high)
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*__vec++ = (_M_table)[(unsigned char)(*__low++)];
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return __high;
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}
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||
</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
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||
<code class="code">__vec</code>.
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||
</p><p>The last two functions again are entirely generic:
|
||
</p><pre class="programlisting">
|
||
const char*
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ctype<char>::
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||
scan_is(mask __m, const char* __low, const char* __high) const throw()
|
||
{
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||
while (__low < __high && !this->is(__m, *__low))
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||
++__low;
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return __low;
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}
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const char*
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ctype<char>::
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||
scan_not(mask __m, const char* __low, const char* __high) const throw()
|
||
{
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||
while (__low < __high && this->is(__m, *__low))
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||
++__low;
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||
return __low;
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||
}
|
||
</pre></div><div class="section"><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="section"><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="section"><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.
|
||
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