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<title>Talking to the UNIX build system: config.m4</title>
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</div><hr /><div id="internals2.buildsys.configunix" class="sect1">
<h2 class="title">Talking to the UNIX build system: config.m4</h2>
<p class="para">
The <var class="filename">config.m4</var> file for an extension tells the UNIX
build system what <var class="filename">configure</var> options your extension
supports, what external libraries and includes you require, and what source
files are to be compiled as part of it. A reference to all the commonly used
autoconf macros, both PHP-specific and those built into autoconf, is given
in the <a href="internals2.apiref.html" class="xref">Zend Engine 2 API reference</a> section.
</p>
<div class="tip"><strong class="tip">Tip</strong>
<p class="para">
The version of <strong class="command">autoconf</strong> you have installed makes a difference
when developing an extension. For PHP 5.3 and earlier, you will have the best results
with <strong class="command">autoconf</strong> version 2.13 but versions up to and including 2.59
will work. For PHP 5.4 and later the oldest <strong class="command">autoconf</strong> version you can
use is 2.59 and you will have better results with later versions.
</p>
</div>
<div class="example" id="internals2.buildsys.configunix.sample-config">
<p><strong>Example #1 An example config.m4 file</strong></p>
<div class="example-contents"><div class="autoconfcode"><pre class="autoconfcode">dnl $Id$
dnl config.m4 for extension example</pre>
</div><div class="autoconfcode"><pre class="autoconfcode">PHP_ARG_WITH(example, for example support,
[ --with-example[=FILE] Include example support. File is the optional path to example-config])
PHP_ARG_ENABLE(example-debug, whether to enable debugging support in example,
[ --enable-example-debug example: Enable debugging support in example], no, no)
PHP_ARG_WITH(example-extra, for extra libraries for example,
[ --with-example-extra=DIR example: Location of extra libraries for example], no, no)
dnl Check whether the extension is enabled at all
if test "$PHP_EXAMPLE" != "no"; then
dnl Check for example-config. First try any path that was given to us, then look in $PATH
AC_MSG_CHECKING([for example-config])
EXAMPLE_CONFIG="example-config"
if test "$PHP_EXAMPLE" != "yes"; then
EXAMPLE_PATH=$PHP_EXAMPLE
else
EXAMPLE_PATH=`$php_shtool path $EXAMPLE_CONFIG`
fi
dnl If a usable example-config was found, use it
if test -f "$EXAMPLE_PATH" && test -x "$EXAMPLE_PATH" && $EXAMPLE_PATH --version > /dev/null 2>&1; then
AC_MSG_RESULT([$EXAMPLE_PATH])
EXAMPLE_LIB_NAME=`$EXAMPLE_PATH --libname`
EXAMPLE_INCDIRS=`$EXAMPLE_PATH --incdirs`
EXAMPLE_LIBS=`$EXAMPLE_PATH --libs`
dnl Check that the library works properly
PHP_CHECK_LIBRARY($EXAMPLE_LIB_NAME, example_critical_function,
[
dnl Add the necessary include dirs
PHP_EVAL_INCLINE($EXAMPLE_INCDIRS)
dnl Add the necessary libraries and library dirs
PHP_EVAL_LIBLINE($EXAMPLE_LIBS, EXAMPLE_SHARED_LIBADD)
],[
dnl Bail out
AC_MSG_ERROR([example library not found. Check config.log for more information.])
],[$EXAMPLE_LIBS]
)
else
dnl No usable example-config, bail
AC_MSG_RESULT([not found])
AC_MSG_ERROR([Please check your example installation.])
fi
dnl Check whether to enable debugging
if test "$PHP_EXAMPLE_DEBUG" != "no"; then
dnl Yes, so set the C macro
AC_DEFINE(USE_EXAMPLE_DEBUG,1,[Include debugging support in example])
fi
dnl Check for the extra support
if test "$PHP_EXAMPLE_EXTRA" != "no"; then
if test "$PHP_EXAMPLE_EXTRA" == "yes"; then
AC_MSG_ERROR([You must specify a path when using --with-example-extra])
fi
PHP_CHECK_LIBRARY(example-extra, example_critical_extra_function,
[
dnl Add the neccessary paths
PHP_ADD_INCLUDE($PHP_EXAMPLE_EXTRA/include)
PHP_ADD_LIBRARY_WITH_PATH(example-extra, $PHP_EXAMPLE_EXTRA/lib, EXAMPLE_SHARED_LIBADD)
AC_DEFINE(HAVE_EXAMPLEEXTRALIB,1,[Whether example-extra support is present and requested])
EXAMPLE_SOURCES="$EXAMPLE_SOURCES example_extra.c"
],[
AC_MSG_ERROR([example-extra lib not found. See config.log for more information.])
],[-L$PHP_EXAMPLE_EXTRA/lib]
)
fi
dnl Finally, tell the build system about the extension and what files are needed
PHP_NEW_EXTENSION(example, example.c $EXAMPLE_SOURCES, $ext_shared)
PHP_SUBST(EXAMPLE_SHARED_LIBADD)
fi</pre>
</div>
</div>
</div>
<div class="sect2" id="internals2.buildsys.configunix.autoconf">
<h3 class="title">A short introduction to autoconf syntax</h3>
<p class="para">
<var class="filename">config.m4</var> files are written using the GNU
<strong class="command">autoconf</strong> syntax. It can be described in a nutshell as
shell scripting augmented by a powerful macro language. Comments are
delimited by the string <em>dnl</em>, and strings are quoted
using left and right brackets (e.g. <em>[</em> and
<em>]</em>). Quoting of strings can be nested as many times as
needed. A full reference to the syntax can be found in the
<strong class="command">autoconf</strong> manual at
<a href="http://www.gnu.org/software/autoconf/manual/" class="link external">» http://www.gnu.org/software/autoconf/manual/</a>.
</p>
</div>
<div class="sect2" id="internals2.buildsys.configunix.php-arg">
<h3 class="title">PHP_ARG_*: Giving users the option</h3>
<p class="para">
The very first thing seen in the example <var class="filename">config.m4</var>
above, aside from a couple of comments, are three lines using
<span class="function"><strong>PHP_ARG_WITH()</strong></span> and <span class="function"><strong>PHP_ARG_ENABLE()</strong></span>.
These provide <strong class="command">configure</strong> with the options and help text
seen when running <strong class="command">./configure --help</strong>. As the names
suggest, the difference between the two is whether they create a
<strong class="option configure">--with-*</strong>
option or an
<strong class="option configure">--enable-*</strong>
option. Every extension should
provide at least one or the other with the extension name, so that users
can choose whether or not to build the extension into PHP. By convention,
<span class="function"><strong>PHP_ARG_WITH()</strong></span> is used for an option which takes a
parameter, such as the location of a library or program required by an
extension, while <span class="function"><strong>PHP_ARG_ENABLE()</strong></span> is used for an option
which represents a simple flag.
</p>
<div class="example" id="internals2.buildsys.configunix.php-arg.configure-out">
<p><strong>Example #2 Sample configure output</strong></p>
<div class="example-contents screen">
<div class="cdata"><pre>
$ ./configure --help
...
--with-example[=FILE] Include example support. FILE is the optional path to example-config
--enable-example-debug example: Enable debugging support in example
--with-example-extra=DIR example: Location of extra libraries for example
...
$ ./configure --with-example=/some/library/path/example-config --disable-example-debug --with-example-extra=/another/library/path
...
checking for example support... yes
checking whether to enable debugging support in example... no
checking for extra libraries for example... /another/library/path
...
</pre></div>
</div>
</div>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Regardless of the order in which options are specified on the command line
when <strong class="command">configure</strong> is called, the checks will be run in the
order they are specified in <var class="filename">config.m4</var>.
</p>
</p></blockquote>
</div>
<div class="sect2" id="internals2.buildsys.configunix.processing">
<h3 class="title">Processing the user's choices</h3>
<p class="para">
Now that <var class="filename">config.m4</var> can provide the user with some
choices of what to do, it's time to act upon those choices. In the example
above, the obvious default for all three options, if any of them are
unspecified, is "no". As a matter of convention, it is best to
use this as the default for the option which enables the extension, as it
will be overridden by <strong class="command">phpize</strong> for extensions built
separately, and should not clutter the extension space by default when
being built into PHP. The code to process the three options is by far the
most complicated.
</p>
<div class="sect3" id="internals2.buildsys.configunix.processing.with-example">
<h4 class="title">Handling the --with-example[=FILE] option</h4>
<p class="para">
The first check made of the
<strong class="option configure">--with-example[=FILE]</strong>
option is whether
it was set at all. As this option controls the inclusion of the entire
extension, if it was unspecified, given in the negative form
(<strong class="option configure">--without-example</strong>
), or given the value
"no", nothing else is done at all. In the example above, it is
specified with the value
<em>/some/library/path/example-config</em>, so the first test
succeeds.
</p>
<p class="para">
Next, the code calls <span class="function"><strong>AC_MSG_CHECKING()</strong></span>, an
<strong class="command">autoconf</strong> macro which outputs a standard
"checking for something" line, and checks whether the user gave
an explicit path to the fictional <strong class="command">example-config</strong>. In
this example, <em>PHP_EXAMPLE</em> got the value
<em>/some/library/path/example-config</em>, which is now copied
into the EXAMPLE_PATH variable. Had the user specified only
<strong class="option configure">--with-example</strong>
, the code would have
executed <strong class="command">$php_shtool path $EXAMPLE_CONFIG</strong>, which would
try to guess the location of <strong class="command">example-config</strong> using the
user's current <em>PATH</em>. Either way, the next step is to
check whether the chosen <em>EXAMPLE_PATH</em> is a regular
file, is executable, and can be run successfully. If so,
<span class="function"><strong>AC_MSG_RESULT()</strong></span> is called, which completes the output
line started by <span class="function"><strong>AC_MSG_CHECKING()</strong></span>. Otherwise,
<span class="function"><strong>AC_MSG_ERROR()</strong></span> is called, which prints the given
message and halts <strong class="command">configure</strong> immediately.
</p>
<p class="para">
The code now determines some site-specific configuration information by
running <strong class="command">example-config</strong> several times. The next call is
to <span class="function"><strong>PHP_CHECK_LIBRARY()</strong></span>, a macro provided by the PHP
buildsystem as a wrapper around <strong class="command">autoconf</strong>'s
<span class="function"><strong>AC_CHECK_LIB()</strong></span>. <span class="function"><strong>PHP_CHECK_LIBRARY()</strong></span>
attempts to compile, link, and run a program which calls the symbol
specified by the second parameter in the library specified by the first,
using the string given in the fifth as extra linker options. If the
attempt succeeds, the script given in the third parameter is run. This
script tells the PHP buildsystem to extract include paths, library paths,
and library names from the raw option strings
<strong class="command">example-config</strong> provided. If the attempt fails, the
script in the fourth parameter is run instead. In this case,
<span class="function"><strong>AC_MSG_ERROR()</strong></span> is called to stop processing.
</p>
</div>
<div class="sect3" id="internals2.buildsys.configunix.processing.enable-example-debug">
<h4 class="title">Handling the --enable-example-debug option</h4>
<p class="para">
Processing the <strong class="option configure">--enable-example-debug</strong>
is
much simpler. A simple check for its truth value is performed. If that
check succeeds, <span class="function"><strong>AC_DEFINE()</strong></span> is called to make the C
macro <em>USE_EXAMPLE_DEBUG</em> available to the source of the
extension. The third parameter is a comment string for
<var class="filename">config.h</var>; it is safe to leave this empty, and often is.
</p>
</div>
<div class="sect3" id="internals2.buildsys.configunix.processing.with-example-extra">
<h4 class="title">Handling the --with-example-extra=DIR option</h4>
<p class="para">
For the sake of this example, the fictional "extra"
functionality requested by the
<strong class="option configure">--with-example-extra=DIR</strong>
option does not
share the fictional <strong class="command">example-config</strong> program, nor does it
have any default paths to search. Therefore, the user is required to
provide the installation prefix of the necessary library. This setup is
somewhat unlikely in a real-world extension, but is considered
illustrative.
</p>
<p class="para">
The code begins in a now-familiar way by checking the truth value of
<em>PHP_EXAMPLE_EXTRA</em>. If a negative form was provided, no
further processing is done; the user did not request extra functionality.
If a positive form was provided without a parameter,
<span class="function"><strong>AC_MSG_ERROR()</strong></span> is called to halt processing. The next
step is another invocation of <span class="function"><strong>PHP_CHECK_LIBRARY()</strong></span>. This
time, since there is no set of predefined compiler options provided,
<span class="function"><strong>PHP_ADD_INCLUDE()</strong></span> and
<span class="function"><strong>PHP_ADD_LIBRARY_WITH_PATH()</strong></span> are used to construct the
necessary include paths, library paths, and library flags for the extra
functionality. <span class="function"><strong>AC_DEFINE()</strong></span> is also called to indicate
to the code that the extra functionality was both requested and available,
and a variable is set to tell later code that there are extra source files
to build. If the check fails, the familiar
<span class="function"><strong>AC_MSG_ERROR()</strong></span> is called. A different way to handle the
failure would have been to call <span class="function"><strong>AC_MSG_WARNING()</strong></span>
instead, e.g.:
</p>
<div class="informalexample">
<div class="example-contents">
<div class="autoconfcode"><pre class="autoconfcode">AC_MSG_WARNING([example-extra lib not found. example will be built without extra functionality.])</pre>
</div>
</div>
</div>
<p class="para">
In this case, <strong class="command">configure</strong> would print a warning message
rather than an error, and continue processing. Which way such failures are
handled is a design decision left to the extension developer.
</p>
</div>
</div>
<div class="sect2" id="internals2.buildsys.configunix.finishing">
<h3 class="title">Telling the buildsystem what was decided</h3>
<p class="para">
With all the necessary includes and libraries specified, with all the
options processed and macros defined, one more thing remains to be done:
The build system must be told to build the extension itself, and which
files are to be used for that. To do this, the
<span class="function"><strong>PHP_NEW_EXTENSION()</strong></span> macro is called. The first parameter
is the name of the extension, which is the same as the name of the
directory containing it. The second parameter is the list of all source
files which are part of the extension. See
<span class="function"><strong>PHP_ADD_BUILD_DIR()</strong></span> for information about adding source
files in subdirectories to the build process. The third parameter should
always be <em>$ext_shared</em>, a value which was determined by
<strong class="command">configure</strong> when <span class="function"><strong>PHP_ARG_WITH()</strong></span> was
called for <strong class="option configure">--with-example[=FILE]</strong>
. The
fourth parameter specifies a "SAPI class", and is only useful for
extensions which require the CGI or CLI SAPIs specifically. It should be
left empty in all other cases. The fifth parameter specifies a list of
flags to be added to <em>CFLAGS</em> while building the
extension; the sixth is a boolean value which, if "yes", will
force the entire extension to be built using <em>$CXX</em>
instead of <em>$CC</em>. All parameters after the third are
optional. Finally, <span class="function"><strong>PHP_SUBST()</strong></span> is called to enable
shared builds of the extension. See <a href="internals2.faq.html" class="xref">Extension FAQs</a> for
more information on disabling support for building an extension in shared
mode.
</p>
</div>
<div class="sect2" id="internals2.buildsys.configunix.counter">
<h3 class="title">The counter extension's config.m4 file</h3>
<p class="para">
The counter extension previously documented has a much simpler
<var class="filename">config.m4</var> file than that described above, as it doesn't
make use of many buildsystem features. This is a preferred method of
operation for any extension that doesn't use an external or bundled library.
</p>
<div class="example" id="internals2.buildsys.configunix.counter.configunix">
<p><strong>Example #3 counter's config.m4 file</strong></p>
<div class="example-contents">
<div class="autoconfcode"><pre class="autoconfcode">dnl</pre>
</div><div class="autoconfcode"><pre class="autoconfcode">$</pre>
</div><div class="autoconfcode"><pre class="autoconfcode">Id$
dnl config.m4 for extension counter
PHP_ARG_ENABLE(counter, for counter support,
[ --enable-counter Include counter support])
dnl Check whether the extension is enabled at all
if test "$PHP_COUNTER" != "no"; then
dnl Finally, tell the build system about the extension and what files are needed
PHP_NEW_EXTENSION(counter, counter.c counter_util.c, $ext_shared)
PHP_SUBST(COUNTER_SHARED_LIBADD)
fi</pre>
</div>
</div>
</div>
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