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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 V1.74.0" /><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.
4 Porting and Maintenance
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="id517404" 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
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" />
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 && autoconf-2.59 &&
27 autoheader-2.59 && 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
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.
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.
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
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>.
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">
78 GLIBCXX_TOPREL_CONFIGURE
81 All the major variable "discovery" is done here. CXX, multilibs,
83 </p><pre class="programlisting">
84 fragments included from elsewhere
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
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
97 </p><pre class="programlisting">
98 GLIBCXX_CHECK_SETRLIMIT_ancilliary
99 GLIBCXX_CHECK_SETRLIMIT
100 GLIBCXX_CHECK_S_ISREG_OR_S_IFREG
104 GLIBCXX_CONFIGURE_TESTSUITE
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
111 GLIBCXX_EXPORT_INSTALL_INFO
113 Installation variables, multilibs, working with the rest of the
114 compiler. Many of the critical variables used in the makefiles are
116 </p><pre class="programlisting">
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
126 GLIBCXX_ENABLE_DEBUG_FLAGS
127 GLIBCXX_ENABLE_LONG_LONG
129 GLIBCXX_ENABLE_SJLJ_EXCEPTIONS
130 GLIBCXX_ENABLE_SYMVERS
131 GLIBCXX_ENABLE_THREADS
133 All the features which can be controlled with enable/disable
134 configure options. Note how they're alphabetized now? Keep them
136 </p><pre class="programlisting">
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!)
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>
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.
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
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).
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">[@<:@=BAR@:>@]</code>, which produces
194 <code class="code">--enable-extra-foo[=BAR]</code>. See the difference? See
195 what it implies to the user?
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://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>
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.
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>
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
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>
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