The config.m4 file for an extension tells the UNIX build system what configure 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 Zend Engine 2 API reference section.
The version of autoconf you have installed makes a difference when developing an extension. For PHP 5.3 and earlier, you will have the best results with autoconf version 2.13 but versions up to and including 2.59 will work. For PHP 5.4 and later the oldest autoconf version you can use is 2.59 and you will have better results with later versions.
Example #1 An example config.m4 file
dnl $Id$ dnl config.m4 for extension example
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
config.m4 files are written using the GNU
autoconf syntax. It can be described in a nutshell as
shell scripting augmented by a powerful macro language. Comments are
delimited by the string
dnl, and strings are quoted
using left and right brackets (e.g.
]). Quoting of strings can be nested as many times as
needed. A full reference to the syntax can be found in the
autoconf manual at
The very first thing seen in the example config.m4 above, aside from a couple of comments, are three lines using PHP_ARG_WITH() and PHP_ARG_ENABLE(). These provide configure with the options and help text seen when running ./configure --help. As the names suggest, the difference between the two is whether they create a --with-* option or an --enable-* 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, PHP_ARG_WITH() is used for an option which takes a parameter, such as the location of a library or program required by an extension, while PHP_ARG_ENABLE() is used for an option which represents a simple flag.
Example #2 Sample configure output
$ ./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 ...
Regardless of the order in which options are specified on the command line when configure is called, the checks will be run in the order they are specified in config.m4.
Now that config.m4 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 phpize 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.
The first check made of the
--with-example[=FILE] 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
(--without-example), or given the value
"no", nothing else is done at all. In the example above, it is
specified with the value
/some/library/path/example-config, so the first test
Next, the code calls AC_MSG_CHECKING(), an
autoconf macro which outputs a standard
"checking for something" line, and checks whether the user gave
an explicit path to the fictional example-config. In
PHP_EXAMPLE got the value
/some/library/path/example-config, which is now copied
into the EXAMPLE_PATH variable. Had the user specified only
--with-example, the code would have
executed $php_shtool path $EXAMPLE_CONFIG, which would
try to guess the location of example-config using the
user's current PATH. Either way, the next step is to
check whether the chosen
EXAMPLE_PATH is a regular
file, is executable, and can be run successfully. If so,
AC_MSG_RESULT() is called, which completes the output
line started by AC_MSG_CHECKING(). Otherwise,
AC_MSG_ERROR() is called, which prints the given
message and halts configure immediately.
The code now determines some site-specific configuration information by running example-config several times. The next call is to PHP_CHECK_LIBRARY(), a macro provided by the PHP buildsystem as a wrapper around autoconf's AC_CHECK_LIB(). PHP_CHECK_LIBRARY() 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 example-config provided. If the attempt fails, the script in the fourth parameter is run instead. In this case, AC_MSG_ERROR() is called to stop processing.
Processing the --enable-example-debug is
much simpler. A simple check for its truth value is performed. If that
check succeeds, AC_DEFINE() is called to make the C
USE_EXAMPLE_DEBUG available to the source of the
extension. The third parameter is a comment string for
config.h; it is safe to leave this empty, and often is.
For the sake of this example, the fictional "extra" functionality requested by the --with-example-extra=DIR option does not share the fictional example-config 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.
The code begins in a now-familiar way by checking the truth value of
PHP_EXAMPLE_EXTRA. 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,
AC_MSG_ERROR() is called to halt processing. The next
step is another invocation of PHP_CHECK_LIBRARY(). This
time, since there is no set of predefined compiler options provided,
PHP_ADD_LIBRARY_WITH_PATH() are used to construct the
necessary include paths, library paths, and library flags for the extra
functionality. AC_DEFINE() 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
AC_MSG_ERROR() is called. A different way to handle the
failure would have been to call AC_MSG_WARNING()
AC_MSG_WARNING([example-extra lib not found. example will be built without extra functionality.])
In this case, configure 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.
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
PHP_NEW_EXTENSION() 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
PHP_ADD_BUILD_DIR() for information about adding source
files in subdirectories to the build process. The third parameter should
$ext_shared, a value which was determined by
configure when PHP_ARG_WITH() was
called for --with-example[=FILE]. 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
CFLAGS while building the
extension; the sixth is a boolean value which, if "yes", will
force the entire extension to be built using
$CC. All parameters after the third are
optional. Finally, PHP_SUBST() is called to enable
shared builds of the extension. See Extension FAQs for
more information on disabling support for building an extension in shared
The counter extension previously documented has a much simpler config.m4 file than that described above, as it doesn't make use of many buildsystem features. This is a preferred method of operation for any extension that doesn't use an external or bundled library.
Example #3 counter's config.m4 file
Id$ 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