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   3 <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 V1.74.3" /><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    " /><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.
   4   Porting and Maintenance
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   6 </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.
   7   Porting and Maintenance
   8   <a id="id492719" class="indexterm"></a>
   9 </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>
  10     As noted <a class="ulink" href="http://gcc.gnu.org/install/prerequisites.html" target="_top">previously</a>,
  11     certain other tools are necessary for hacking on files that
  12     control configure (<code class="code">configure.ac</code>,
  13     <code class="code">acinclude.m4</code>) and make
  14     (<code class="code">Makefile.am</code>). These additional tools
  15     (<code class="code">automake</code>, and <code class="code">autoconf</code>) are further
  16     described in detail in their respective manuals. All the libraries
  17     in GCC try to stay in sync with each other in terms of versions of
  18     the auto-tools used, so please try to play nicely with the
  19     neighbors.
  20   </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">
  21   <img src="../images/confdeps.png" alt="Dependency Graph Configure to Build Files" />
  22   </pre><p>
  23     Regenerate all generated files by using the command sequence
  24     <code class="code">"autoreconf"</code> at the top level of the libstdc++ source
  25     directory. The following will also work, but is much more complex:
  26     <code class="code">"aclocal-1.7 &amp;&amp; autoconf-2.59 &amp;&amp;
  27     autoheader-2.59 &amp;&amp; automake-1.7"</code> The version
  28     numbers may be absent entirely or otherwise vary depending on
  29     <a class="ulink" href="http://gcc.gnu.org/install/prerequisites.html" target="_top">the
  30     current requirements</a> and your vendor's choice of
  31     installation names.
  32   </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>
  33     Until that glorious day when we can use AC_TRY_LINK with a
  34     cross-compiler, we have to hardcode the results of what the tests
  35     would have shown if they could be run.  So we have an inflexible
  36     mess like crossconfig.m4.
  37   </p><p>
  38     Wouldn't it be nice if we could store that information in files
  39     like configure.host, which can be modified without needing to
  40     regenerate anything, and can even be tweaked without really
  41     knowing how the configury all works?  Perhaps break the pieces of
  42     crossconfig.m4 out and place them in their appropriate
  43     config/{cpu,os} directory.
  44   </p><p>
  45     Alas, writing macros like
  46     "<code class="code">AC_DEFINE(HAVE_A_NICE_DAY)</code>" can only be done inside
  47     files which are passed through autoconf.  Files which are pure
  48     shell script can be source'd at configure time.  Files which
  49     contain autoconf macros must be processed with autoconf.  We could
  50     still try breaking the pieces out into "config/*/cross.m4" bits,
  51     for instance, but then we would need arguments to aclocal/autoconf
  52     to properly find them all when generating configure.  I would
  53     discourage that.
  54 </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>
  55     Most comments should use {octothorpes, shibboleths, hash marks,
  56     pound signs, whatever} rather than "dnl".  Nearly all comments in
  57     configure.ac should.  Comments inside macros written in ancilliary
  58     .m4 files should.  About the only comments which should
  59     <span class="emphasis"><em>not</em></span> use #, but use dnl instead, are comments
  60     <span class="emphasis"><em>outside</em></span> our own macros in the ancilliary
  61     files.  The difference is that # comments show up in
  62     <code class="code">configure</code> (which is most helpful for debugging),
  63     while dnl'd lines just vanish.  Since the macros in ancilliary
  64     files generate code which appears in odd places, their "outside"
  65     comments tend to not be useful while reading
  66     <code class="code">configure</code>.
  67   </p><p>
  68     Do not use any <code class="code">$target*</code> variables, such as
  69     <code class="code">$target_alias</code>.  The single exception is in
  70     configure.ac, for automake+dejagnu's sake.
  71   </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>
  72     The nice thing about acinclude.m4/aclocal.m4 is that macros aren't
  73     actually performed/called/expanded/whatever here, just loaded.  So
  74     we can arrange the contents however we like.  As of this writing,
  75     acinclude.m4 is arranged as follows:
  76   </p><pre class="programlisting">
  77     GLIBCXX_CHECK_HOST
  78     GLIBCXX_TOPREL_CONFIGURE
  79     GLIBCXX_CONFIGURE
  80   </pre><p>
  81     All the major variable "discovery" is done here.  CXX, multilibs,
  82     etc.
  83   </p><pre class="programlisting">
  84     fragments included from elsewhere
  85   </pre><p>
  86     Right now, "fragments" == "the math/linkage bits".
  87   </p><pre class="programlisting">
  88     GLIBCXX_CHECK_COMPILER_FEATURES
  89     GLIBCXX_CHECK_LINKER_FEATURES
  90     GLIBCXX_CHECK_WCHAR_T_SUPPORT
  91 </pre><p>
  92   Next come extra compiler/linker feature tests.  Wide character
  93   support was placed here because I couldn't think of another place
  94   for it.  It will probably get broken apart like the math tests,
  95   because we're still disabling wchars on systems which could actually
  96   support them.
  97 </p><pre class="programlisting">
  98     GLIBCXX_CHECK_SETRLIMIT_ancilliary
  99     GLIBCXX_CHECK_SETRLIMIT
 100     GLIBCXX_CHECK_S_ISREG_OR_S_IFREG
 101     GLIBCXX_CHECK_POLL
 102     GLIBCXX_CHECK_WRITEV
 103
 104     GLIBCXX_CONFIGURE_TESTSUITE
 105 </pre><p>
 106   Feature tests which only get used in one place.  Here, things used
 107   only in the testsuite, plus a couple bits used in the guts of I/O.
 108 </p><pre class="programlisting">
 109     GLIBCXX_EXPORT_INCLUDES
 110     GLIBCXX_EXPORT_FLAGS
 111     GLIBCXX_EXPORT_INSTALL_INFO
 112 </pre><p>
 113   Installation variables, multilibs, working with the rest of the
 114   compiler.  Many of the critical variables used in the makefiles are
 115   set here.
 116 </p><pre class="programlisting">
 117     GLIBGCC_ENABLE
 118     GLIBCXX_ENABLE_C99
 119     GLIBCXX_ENABLE_CHEADERS
 120     GLIBCXX_ENABLE_CLOCALE
 121     GLIBCXX_ENABLE_CONCEPT_CHECKS
 122     GLIBCXX_ENABLE_CSTDIO
 123     GLIBCXX_ENABLE_CXX_FLAGS
 124     GLIBCXX_ENABLE_C_MBCHAR
 125     GLIBCXX_ENABLE_DEBUG
 126     GLIBCXX_ENABLE_DEBUG_FLAGS
 127     GLIBCXX_ENABLE_LONG_LONG
 128     GLIBCXX_ENABLE_PCH
 129     GLIBCXX_ENABLE_SJLJ_EXCEPTIONS
 130     GLIBCXX_ENABLE_SYMVERS
 131     GLIBCXX_ENABLE_THREADS
 132 </pre><p>
 133   All the features which can be controlled with enable/disable
 134   configure options.  Note how they're alphabetized now?  Keep them
 135   like that.  :-)
 136 </p><pre class="programlisting">
 137     AC_LC_MESSAGES
 138     libtool bits
 139 </pre><p>
 140   Things which we don't seem to use directly, but just has to be
 141   present otherwise stuff magically goes wonky.
 142 </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>
 143     All the GLIBCXX_ENABLE_FOO macros use a common helper,
 144     GLIBCXX_ENABLE.  (You don't have to use it, but it's easy.)  The
 145     helper does two things for us:
 146   </p><div class="orderedlist"><ol type="1"><li><p>
 147      Builds the call to the AC_ARG_ENABLE macro, with --help text
 148      properly quoted and aligned.  (Death to changequote!)
 149    </p></li><li><p>
 150      Checks the result against a list of allowed possibilities, and
 151      signals a fatal error if there's no match.  This means that the
 152      rest of the GLIBCXX_ENABLE_FOO macro doesn't need to test for
 153      strange arguments, nor do we need to protect against
 154      empty/whitespace strings with the <code class="code">"x$foo" = "xbar"</code>
 155      idiom.
 156    </p></li></ol></div><p>Doing these things correctly takes some extra autoconf/autom4te code,
 157    which made our macros nearly illegible.  So all the ugliness is factored
 158    out into this one helper macro.
 159 </p><p>Many of the macros take an argument, passed from when they are expanded
 160    in configure.ac.  The argument controls the default value of the
 161    enable/disable switch.  Previously, the arguments themselves had defaults.
 162    Now they don't, because that's extra complexity with zero gain for us.
 163 </p><p>There are three "overloaded signatures".  When reading the descriptions
 164    below, keep in mind that the brackets are autoconf's quotation characters,
 165    and that they will be stripped.  Examples of just about everything occur
 166    in acinclude.m4, if you want to look.
 167 </p><pre class="programlisting">
 168     GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING)
 169     GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING, permit a|b|c)
 170     GLIBCXX_ENABLE (FEATURE, DEFAULT, HELP-ARG, HELP-STRING, SHELL-CODE-HANDLER)
 171 </pre><div class="itemizedlist"><ul type="disc"><li><p>
 172      FEATURE is the string that follows --enable.  The results of the
 173      test (such as it is) will be in the variable $enable_FEATURE,
 174      where FEATURE has been squashed.  Example:
 175      <code class="code">[extra-foo]</code>, controlled by the --enable-extra-foo
 176      option and stored in $enable_extra_foo.
 177    </p></li><li><p>
 178      DEFAULT is the value to store in $enable_FEATURE if the user does
 179      not pass --enable/--disable.  It should be one of the permitted
 180      values passed later.  Examples: <code class="code">[yes]</code>, or
 181      <code class="code">[bar]</code>, or <code class="code">[$1]</code> (which passes the
 182      argument given to the GLIBCXX_ENABLE_FOO macro as the
 183      default).
 184    </p><p>
 185      For cases where we need to probe for particular models of things,
 186      it is useful to have an undocumented "auto" value here (see
 187      GLIBCXX_ENABLE_CLOCALE for an example).
 188    </p></li><li><p>
 189      HELP-ARG is any text to append to the option string itself in the
 190      --help output.  Examples: <code class="code">[]</code> (i.e., an empty string,
 191      which appends nothing), <code class="code">[=BAR]</code>, which produces
 192      <code class="code">--enable-extra-foo=BAR</code>, and
 193      <code class="code">[@&lt;:@=BAR@:&gt;@]</code>, which produces
 194      <code class="code">--enable-extra-foo[=BAR]</code>.  See the difference?  See
 195      what it implies to the user?
 196    </p><p>
 197      If you're wondering what that line noise in the last example was,
 198      that's how you embed autoconf special characters in output text.
 199      They're called <a class="ulink" href="http://ftp.gnu.org/pub/old-gnu/Manuals/autoconf-2.57/html_mono/autoconf.html#SEC95" target="_top"><span class="emphasis"><em>quadrigraphs</em></span></a>
 200      and you should use them whenever necessary.
 201  </p></li><li><p>HELP-STRING is what you think it is.  Do not include the
 202    "default" text like we used to do; it will be done for you by
 203    GLIBCXX_ENABLE.  By convention, these are not full English
 204    sentences.  Example: [turn on extra foo]
 205    </p></li></ul></div><p>
 206   With no other arguments, only the standard autoconf patterns are
 207   allowed: "<code class="code">--{enable,disable}-foo[={yes,no}]</code>" The
 208   $enable_FEATURE variable is guaranteed to equal either "yes" or "no"
 209   after the macro.  If the user tries to pass something else, an
 210   explanatory error message will be given, and configure will halt.
 211 </p><p>
 212   The second signature takes a fifth argument, "<code class="code">[permit
 213   a | b | c | ...]</code>"
 214   This allows <span class="emphasis"><em>a</em></span> or <span class="emphasis"><em>b</em></span> or
 215   ... after the equals sign in the option, and $enable_FEATURE is
 216   guaranteed to equal one of them after the macro.  Note that if you
 217   want to allow plain --enable/--disable with no "=whatever", you must
 218   include "yes" and "no" in the list of permitted values.  Also note
 219   that whatever you passed as DEFAULT must be in the list.  If the
 220   user tries to pass something not on the list, a semi-explanatory
 221   error message will be given, and configure will halt.  Example:
 222   <code class="code">[permit generic|gnu|ieee_1003.1-2001|yes|no|auto]</code>
 223 </p><p>
 224   The third signature takes a fifth argument.  It is arbitrary shell
 225   code to execute if the user actually passes the enable/disable
 226   option.  (If the user does not, the default is used.  Duh.)  No
 227   argument checking at all is done in this signature.  See
 228   GLIBCXX_ENABLE_CXX_FLAGS for an example of handling, and an error
 229   message.
 230 </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>