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+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Appendix B. Porting and Maintenance</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="spine.html" title="The GNU C++ Library" /><link rel="prev" href="source_design_notes.html" title="Design Notes" /><link rel="next" href="internals.html" title="Porting to New Hardware or Operating Systems" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Appendix B.
+ Porting and Maintenance
+
+</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="source_design_notes.html">Prev</a> </td><th width="60%" align="center">The GNU C++ Library</th><td width="20%" align="right"> <a accesskey="n" href="internals.html">Next</a></td></tr></table><hr /></div><div class="appendix" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="appendix.porting"></a>Appendix B.
+ Porting and Maintenance
+ <a id="id517404" class="indexterm"></a>
+</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="appendix_porting.html#appendix.porting.build_hacking">Configure and Build Hacking</a></span></dt><dd><dl><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.prereq">Prerequisites</a></span></dt><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.map">Overview: What Comes from Where</a></span></dt><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.scripts">Storing Information in non-AC files (like configure.host)</a></span></dt><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.conventions">Coding and Commenting Conventions</a></span></dt><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.acinclude">The acinclude.m4 layout</a></span></dt><dt><span class="sect2"><a href="appendix_porting.html#build_hacking.enable">GLIBCXX_ENABLE, the --enable maker</a></span></dt></dl></dd><dt><span class="sect1"><a href="internals.html">Porting to New Hardware or Operating Systems</a></span></dt><dd><dl><dt><span class="sect2"><a href="internals.html#internals.os">Operating System</a></span></dt><dt><span class="sect2"><a href="internals.html#internals.cpu">CPU</a></span></dt><dt><span class="sect2"><a href="internals.html#internals.char_types">Character Types</a></span></dt><dt><span class="sect2"><a href="internals.html#internals.thread_safety">Thread Safety</a></span></dt><dt><span class="sect2"><a href="internals.html#internals.numeric_limits">Numeric Limits</a></span></dt><dt><span class="sect2"><a href="internals.html#internals.libtool">Libtool</a></span></dt></dl></dd><dt><span class="sect1"><a href="abi.html">ABI Policy and Guidelines</a></span></dt><dd><dl><dt><span class="sect2"><a href="abi.html#abi.cxx_interface">The C++ Interface</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.versioning">Versioning</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.changes_allowed">Allowed Changes</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.changes_no">Prohibited Changes</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.impl">Implementation</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.testing">Testing</a></span></dt><dt><span class="sect2"><a href="abi.html#abi.issues">Outstanding Issues</a></span></dt></dl></dd><dt><span class="sect1"><a href="api.html">API Evolution and Deprecation History</a></span></dt><dd><dl><dt><span class="sect2"><a href="api.html#api.rel_300">3.0</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_310">3.1</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_320">3.2</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_330">3.3</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_340">3.4</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_400">4.0</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_410">4.1</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_420">4.2</a></span></dt><dt><span class="sect2"><a href="api.html#api.rel_430">4.3</a></span></dt></dl></dd><dt><span class="sect1"><a href="backwards.html">Backwards Compatibility</a></span></dt><dd><dl><dt><span class="sect2"><a href="backwards.html#backwards.first">First</a></span></dt><dt><span class="sect2"><a href="backwards.html#backwards.second">Second</a></span></dt><dt><span class="sect2"><a href="backwards.html#backwards.third">Third</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="appendix.porting.build_hacking"></a>Configure and Build Hacking</h2></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.prereq"></a>Prerequisites</h3></div></div></div><p>
+ As noted <a class="ulink" href="http://gcc.gnu.org/install/prerequisites.html" target="_top">previously</a>,
+ certain other tools are necessary for hacking on files that
+ control configure (<code class="code">configure.ac</code>,
+ <code class="code">acinclude.m4</code>) and make
+ (<code class="code">Makefile.am</code>). These additional tools
+ (<code class="code">automake</code>, and <code class="code">autoconf</code>) are further
+ described in detail in their respective manuals. All the libraries
+ in GCC try to stay in sync with each other in terms of versions of
+ the auto-tools used, so please try to play nicely with the
+ neighbors.
+ </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.map"></a>Overview: What Comes from Where</h3></div></div></div><pre class="screen">
+ <img src="../images/confdeps.png" alt="Dependency Graph Configure to Build Files" />
+ </pre><p>
+ Regenerate all generated files by using the command sequence
+ <code class="code">"autoreconf"</code> at the top level of the libstdc++ source
+ directory. The following will also work, but is much more complex:
+ <code class="code">"aclocal-1.7 && autoconf-2.59 &&
+ autoheader-2.59 && automake-1.7"</code> The version
+ numbers may be absent entirely or otherwise vary depending on
+ <a class="ulink" href="http://gcc.gnu.org/install/prerequisites.html" target="_top">the
+ current requirements</a> and your vendor's choice of
+ installation names.
+ </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.scripts"></a>Storing Information in non-AC files (like configure.host)</h3></div></div></div><p>
+ Until that glorious day when we can use AC_TRY_LINK with a
+ cross-compiler, we have to hardcode the results of what the tests
+ would have shown if they could be run. So we have an inflexible
+ mess like crossconfig.m4.
+ </p><p>
+ Wouldn't it be nice if we could store that information in files
+ like configure.host, which can be modified without needing to
+ regenerate anything, and can even be tweaked without really
+ knowing how the configury all works? Perhaps break the pieces of
+ crossconfig.m4 out and place them in their appropriate
+ config/{cpu,os} directory.
+ </p><p>
+ Alas, writing macros like
+ "<code class="code">AC_DEFINE(HAVE_A_NICE_DAY)</code>" can only be done inside
+ files which are passed through autoconf. Files which are pure
+ shell script can be source'd at configure time. Files which
+ contain autoconf macros must be processed with autoconf. We could
+ still try breaking the pieces out into "config/*/cross.m4" bits,
+ for instance, but then we would need arguments to aclocal/autoconf
+ to properly find them all when generating configure. I would
+ discourage that.
+</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.conventions"></a>Coding and Commenting Conventions</h3></div></div></div><p>
+ Most comments should use {octothorpes, shibboleths, hash marks,
+ pound signs, whatever} rather than "dnl". Nearly all comments in
+ configure.ac should. Comments inside macros written in ancilliary
+ .m4 files should. About the only comments which should
+ <span class="emphasis"><em>not</em></span> use #, but use dnl instead, are comments
+ <span class="emphasis"><em>outside</em></span> our own macros in the ancilliary
+ files. The difference is that # comments show up in
+ <code class="code">configure</code> (which is most helpful for debugging),
+ while dnl'd lines just vanish. Since the macros in ancilliary
+ files generate code which appears in odd places, their "outside"
+ comments tend to not be useful while reading
+ <code class="code">configure</code>.
+ </p><p>
+ Do not use any <code class="code">$target*</code> variables, such as
+ <code class="code">$target_alias</code>. The single exception is in
+ configure.ac, for automake+dejagnu's sake.
+ </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.acinclude"></a>The acinclude.m4 layout</h3></div></div></div><p>
+ The nice thing about acinclude.m4/aclocal.m4 is that macros aren't
+ actually performed/called/expanded/whatever here, just loaded. So
+ we can arrange the contents however we like. As of this writing,
+ acinclude.m4 is arranged as follows:
+ </p><pre class="programlisting">
+ GLIBCXX_CHECK_HOST
+ GLIBCXX_TOPREL_CONFIGURE
+ GLIBCXX_CONFIGURE
+ </pre><p>
+ All the major variable "discovery" is done here. CXX, multilibs,
+ etc.
+ </p><pre class="programlisting">
+ fragments included from elsewhere
+ </pre><p>
+ Right now, "fragments" == "the math/linkage bits".
+ </p><pre class="programlisting">
+ GLIBCXX_CHECK_COMPILER_FEATURES
+ GLIBCXX_CHECK_LINKER_FEATURES
+ GLIBCXX_CHECK_WCHAR_T_SUPPORT
+</pre><p>
+ Next come extra compiler/linker feature tests. Wide character
+ support was placed here because I couldn't think of another place
+ for it. It will probably get broken apart like the math tests,
+ because we're still disabling wchars on systems which could actually
+ support them.
+</p><pre class="programlisting">
+ GLIBCXX_CHECK_SETRLIMIT_ancilliary
+ GLIBCXX_CHECK_SETRLIMIT
+ GLIBCXX_CHECK_S_ISREG_OR_S_IFREG
+ GLIBCXX_CHECK_POLL
+ GLIBCXX_CHECK_WRITEV
+
+ GLIBCXX_CONFIGURE_TESTSUITE
+</pre><p>
+ Feature tests which only get used in one place. Here, things used
+ only in the testsuite, plus a couple bits used in the guts of I/O.
+</p><pre class="programlisting">
+ GLIBCXX_EXPORT_INCLUDES
+ GLIBCXX_EXPORT_FLAGS
+ GLIBCXX_EXPORT_INSTALL_INFO
+</pre><p>
+ Installation variables, multilibs, working with the rest of the
+ compiler. Many of the critical variables used in the makefiles are
+ set here.
+</p><pre class="programlisting">
+ GLIBGCC_ENABLE
+ GLIBCXX_ENABLE_C99
+ GLIBCXX_ENABLE_CHEADERS
+ GLIBCXX_ENABLE_CLOCALE
+ GLIBCXX_ENABLE_CONCEPT_CHECKS
+ GLIBCXX_ENABLE_CSTDIO
+ GLIBCXX_ENABLE_CXX_FLAGS
+ GLIBCXX_ENABLE_C_MBCHAR
+ GLIBCXX_ENABLE_DEBUG
+ GLIBCXX_ENABLE_DEBUG_FLAGS
+ GLIBCXX_ENABLE_LONG_LONG
+ GLIBCXX_ENABLE_PCH
+ GLIBCXX_ENABLE_SJLJ_EXCEPTIONS
+ GLIBCXX_ENABLE_SYMVERS
+ GLIBCXX_ENABLE_THREADS
+</pre><p>
+ All the features which can be controlled with enable/disable
+ configure options. Note how they're alphabetized now? Keep them
+ like that. :-)
+</p><pre class="programlisting">
+ AC_LC_MESSAGES
+ libtool bits
+</pre><p>
+ Things which we don't seem to use directly, but just has to be
+ present otherwise stuff magically goes wonky.
+</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="build_hacking.enable"></a><code class="constant">GLIBCXX_ENABLE</code>, the <code class="literal">--enable</code> maker</h3></div></div></div><p>
+ All the GLIBCXX_ENABLE_FOO macros use a common helper,
+ GLIBCXX_ENABLE. (You don't have to use it, but it's easy.) The
+ helper does two things for us:
+ </p><div class="orderedlist"><ol type="1"><li><p>
+ Builds the call to the AC_ARG_ENABLE macro, with --help text
+ properly quoted and aligned. (Death to changequote!)
+ </p></li><li><p>
+ Checks the result against a list of allowed possibilities, and
+ signals a fatal error if there's no match. This means that the
+ rest of the GLIBCXX_ENABLE_FOO macro doesn't need to test for
+ strange arguments, nor do we need to protect against
+ empty/whitespace strings with the <code class="code">"x$foo" = "xbar"</code>
+ idiom.
+ </p></li></ol></div><p>Doing these things correctly takes some extra autoconf/autom4te code,
+ which made our macros nearly illegible. So all the ugliness is factored
+ out into this one helper macro.
+</p><p>Many of the macros take an argument, passed from when they are expanded
+ in configure.ac. The argument controls the default value of the
+ enable/disable switch. Previously, the arguments themselves had defaults.
+ Now they don't, because that's extra complexity with zero gain for us.
+</p><p>There are three "overloaded signatures". When reading the descriptions
+ below, keep in mind that the brackets are autoconf's quotation characters,
+ and that they will be stripped. Examples of just about everything occur
+ in acinclude.m4, if you want to look.
+</p><pre class="programlisting">
+ GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING)
+ GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING, permit a|b|c)
+ GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING, SHELL-CODE-HANDLER)
+</pre><div class="itemizedlist"><ul type="disc"><li><p>
+ FEATURE is the string that follows --enable. The results of the
+ test (such as it is) will be in the variable $enable_FEATURE,
+ where FEATURE has been squashed. Example:
+ <code class="code">[extra-foo]</code>, controlled by the --enable-extra-foo
+ option and stored in $enable_extra_foo.
+ </p></li><li><p>
+ DEFAULT is the value to store in $enable_FEATURE if the user does
+ not pass --enable/--disable. It should be one of the permitted
+ values passed later. Examples: <code class="code">[yes]</code>, or
+ <code class="code">[bar]</code>, or <code class="code">[$1]</code> (which passes the
+ argument given to the GLIBCXX_ENABLE_FOO macro as the
+ default).
+ </p><p>
+ For cases where we need to probe for particular models of things,
+ it is useful to have an undocumented "auto" value here (see
+ GLIBCXX_ENABLE_CLOCALE for an example).
+ </p></li><li><p>
+ HELP-ARG is any text to append to the option string itself in the
+ --help output. Examples: <code class="code">[]</code> (i.e., an empty string,
+ which appends nothing), <code class="code">[=BAR]</code>, which produces
+ <code class="code">--enable-extra-foo=BAR</code>, and
+ <code class="code">[@<:@=BAR@:>@]</code>, which produces
+ <code class="code">--enable-extra-foo[=BAR]</code>. See the difference? See
+ what it implies to the user?
+ </p><p>
+ If you're wondering what that line noise in the last example was,
+ that's how you embed autoconf special characters in output text.
+ They're called <a class="ulink" href="http://www.gnu.org/software/autoconf/manual/autoconf-2.57/html_node/autoconf_95.html#SEC95" target="_top"><span class="emphasis"><em>quadrigraphs</em></span></a>
+ and you should use them whenever necessary.
+ </p></li><li><p>HELP-STRING is what you think it is. Do not include the
+ "default" text like we used to do; it will be done for you by
+ GLIBCXX_ENABLE. By convention, these are not full English
+ sentences. Example: [turn on extra foo]
+ </p></li></ul></div><p>
+ With no other arguments, only the standard autoconf patterns are
+ allowed: "<code class="code">--{enable,disable}-foo[={yes,no}]</code>" The
+ $enable_FEATURE variable is guaranteed to equal either "yes" or "no"
+ after the macro. If the user tries to pass something else, an
+ explanatory error message will be given, and configure will halt.
+</p><p>
+ The second signature takes a fifth argument, "<code class="code">[permit
+ a | b | c | ...]</code>"
+ This allows <span class="emphasis"><em>a</em></span> or <span class="emphasis"><em>b</em></span> or
+ ... after the equals sign in the option, and $enable_FEATURE is
+ guaranteed to equal one of them after the macro. Note that if you
+ want to allow plain --enable/--disable with no "=whatever", you must
+ include "yes" and "no" in the list of permitted values. Also note
+ that whatever you passed as DEFAULT must be in the list. If the
+ user tries to pass something not on the list, a semi-explanatory
+ error message will be given, and configure will halt. Example:
+ <code class="code">[permit generic|gnu|ieee_1003.1-2001|yes|no|auto]</code>
+</p><p>
+ The third signature takes a fifth argument. It is arbitrary shell
+ code to execute if the user actually passes the enable/disable
+ option. (If the user does not, the default is used. Duh.) No
+ argument checking at all is done in this signature. See
+ GLIBCXX_ENABLE_CXX_FLAGS for an example of handling, and an error
+ message.
+</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="source_design_notes.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="spine.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="internals.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Design Notes </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Porting to New Hardware or Operating Systems</td></tr></table></div></body></html>
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