PHP's Automatic Build System

PHP 4 features an automatic build system that's very flexible. All modules reside in a subdirectory of the ext directory. In addition to its own sources, each module consists of a config.m4 file, for extension configuration. (for example, see

All these stub files are generated automatically, along with .cvsignore, by a little shell script named ext_skel that resides in the ext directory. As argument it takes the name of the module that you want to create. The shell script then creates a directory of the same name, along with the appropriate stub files.

Step by step, the process looks like this:

:~/cvs/php4/ext:> ./ext_skel --extname=my_module
Creating directory my_module
Creating basic files: config.m4 .cvsignore my_module.c php_my_module.h CREDITS EXPERIMENTAL tests/001.phpt my_module.php [done].

To use your new extension, you will have to execute the following steps:

1.  $ cd ..
2.  $ vi ext/my_module/config.m4
3.  $ ./buildconf
4.  $ ./configure --[with|enable]-my_module
5.  $ make
6.  $ ./php -f ext/my_module/my_module.php
7.  $ vi ext/my_module/my_module.c
8.  $ make

Repeat steps 3-6 until you are satisfied with ext/my_module/config.m4 and
step 6 confirms that your module is compiled into PHP. Then, start writing
code and repeat the last two steps as often as necessary.
This instruction creates the aforementioned files. To include the new module in the automatic configuration and build process, you have to run buildconf, which regenerates the configure script by searching through the ext directory and including all found config.m4 files.

The default config.m4 shown in Example 46-1 is a bit more complex:

Example 46-1. The default config.m4.

dnl $Id: build.xml,v 1.1 2005/08/21 16:27:06 goba Exp $
dnl config.m4 for extension my_module

dnl Comments in this file start with the string 'dnl'.
dnl Remove where necessary. This file will not work
dnl without editing.

dnl If your extension references something external, use with:

dnl PHP_ARG_WITH(my_module, for my_module support,
dnl Make sure that the comment is aligned:
dnl [  --with-my_module             Include my_module support])

dnl Otherwise use enable:

dnl PHP_ARG_ENABLE(my_module, whether to enable my_module support,
dnl Make sure that the comment is aligned:
dnl [  --enable-my_module           Enable my_module support])

if test "$PHP_MY_MODULE" != "no"; then
  dnl Write more examples of tests here...

  dnl # --with-my_module -> check with-path
  dnl SEARCH_PATH="/usr/local /usr"     # you might want to change this
  dnl SEARCH_FOR="/include/my_module.h"  # you most likely want to change this
  dnl if test -r $PHP_MY_MODULE/; then # path given as parameter
  dnl else # search default path list
  dnl   AC_MSG_CHECKING([for my_module files in default path])
  dnl   for i in $SEARCH_PATH ; do
  dnl     if test -r $i/$SEARCH_FOR; then
  dnl       MY_MODULE_DIR=$i
  dnl       AC_MSG_RESULT(found in $i)
  dnl     fi
  dnl   done
  dnl fi
  dnl if test -z "$MY_MODULE_DIR"; then
  dnl   AC_MSG_RESULT([not found])
  dnl   AC_MSG_ERROR([Please reinstall the my_module distribution])
  dnl fi

  dnl # --with-my_module -> add include path

  dnl # --with-my_module -> chech for lib and symbol presence
  dnl LIBNAME=my_module # you may want to change this
  dnl LIBSYMBOL=my_module # you most likely want to change this 

  dnl [
  dnl ],[
  dnl   AC_MSG_ERROR([wrong my_module lib version or lib not found])
  dnl ],[
  dnl   -L$MY_MODULE_DIR/lib -lm -ldl
  dnl ])

  PHP_NEW_EXTENSION(my_module, my_module.c, $ext_shared)

If you're unfamiliar with M4 files (now is certainly a good time to get familiar), this might be a bit confusing at first; but it's actually quite easy.

Note: Everything prefixed with dnl is treated as a comment and is not parsed.

The config.m4 file is responsible for parsing the command-line options passed to configure at configuration time. This means that it has to check for required external files and do similar configuration and setup tasks.

The default file creates two configuration directives in the configure script: --with-my_module and --enable-my_module. Use the first option when referring external files (such as the --with-apache directive that refers to the Apache directory). Use the second option when the user simply has to decide whether to enable your extension. Regardless of which option you use, you should uncomment the other, unnecessary one; that is, if you're using --enable-my_module, you should remove support for --with-my_module, and vice versa.

By default, the config.m4 file created by ext_skel accepts both directives and automatically enables your extension. Enabling the extension is done by using the PHP_EXTENSION macro. To change the default behavior to include your module into the PHP binary when desired by the user (by explicitly specifying --enable-my_module or --with-my_module), change the test for $PHP_MY_MODULE to == "yes":

if test "$PHP_MY_MODULE" == "yes"; then dnl
    Action.. PHP_EXTENSION(my_module, $ext_shared)
This would require you to use --enable-my_module each time when reconfiguring and recompiling PHP.

Note: Be sure to run buildconf every time you change config.m4!

We'll go into more details on the M4 macros available to your configuration scripts later in this chapter. For now, we'll simply use the default files.