Building PHP

This chapter explains how you can compile PHP in a way that is suitable for development of extensions or core modifications. We will only cover builds on Unixoid systems. If you wish to build PHP on Windows, you should take a look at the step-by-step build instructions in the PHP wiki [1].

This chapter also provides an overview of how the PHP build system works and which tools it uses, but a detailed description is outside the scope of this book.

Why not use packages?

If you are currently using PHP, you likely installed it through your package manager, using a command like sudo apt-get install php. Before explaining the actual compilation you should first understand why doing your own compile is necessary and you can’t just use a prebuilt package. There are multiple reasons for this:

Firstly, the prebuilt package only contains the resulting binaries, but misses other things that are necessary to compile extensions, e.g. header files. This can be easily remedied by installing a development package, which is typically called php-dev. To facilitate debugging with valgrind or gdb one could additionally install debug symbols, which are usually available as another package called php-dbg.

But even if you install headers and debug symbols, you’ll still be working with a release build of PHP. This means that it will be built with high optimization level, which can make debugging very hard. Furthermore release builds do not enable assertions and do not generate warnings about memory leaks. Additionally, prebuilt packages don’t enable thread safety, which may be helpful to ensure your extension builds in a thread-safe configuration.

Another issue is that nearly all distributions apply additional patches to PHP. In some cases these patches only contain minor changes related to configuration, but some distributions make use of highly intrusive patches like Suhosin. Some of these patches are known to introduce incompatibilities with low-level extensions like opcache.

PHP only provides support for the software as provided on and not for the distribution-modified versions. If you want to report bugs, submit patches or make use of our help channels for extension-writing, you should always work against the official PHP version. When we talk about “PHP” in this book, we’re always referring to the officially supported version.

Obtaining the source code

Before you can build PHP you first need to obtain its source code. There are two ways to do this: You can either download an archive from PHP’s download page or clone the git repository from Github.

The build process is slightly different for both cases: The git repository doesn’t bundle a configure script, so you’ll need to generate it using the buildconf script, which makes use of autoconf. Furthermore the git repository does not contain a pregenerated lexer and parser, so you’ll also need to have re2c and bison installed.

We recommend to checkout out the source code from git, because this will provide you with an easy way to keep your installation updated and to try your code with different versions. A git checkout is also required if you want to submit patches or pull requests for PHP.

To clone the repository, run the following commands in your shell:

~> git clone
~> cd php-src
# by default you will be on the master branch, which is the current
# development version. You can check out a stable branch instead:
~/php-src> git checkout PHP-8.1

If you have issues with the git checkout, take a look at the Git FAQ on the PHP wiki. The Git FAQ also explains how to setup git if you want to contribute to PHP itself. Furthermore it contains instructions on setting up multiple working directories for different PHP versions. This can be very useful if you need to test your extensions or changes against multiple PHP versions and configurations.

Before continuing, you should also install some basic build dependencies with your package manager (you’ll likely already have the first three installed by default):

  • gcc and g++ or some other compiler toolchain.

  • libc-dev, which provides the C standard library, including headers.

  • make, which is the build-management tool PHP uses.

  • autoconf, which is used to generate the configure script.

    • 2.59 or higher (for PHP 7.0-7.1)

    • 2.64 or higher (for PHP 7.2)

    • 2.68 or higher (for PHP 7.3 and higher)

  • libtool, which helps manage shared libraries.

  • bison which is used to generate the PHP parser.

    • 2.4 or higher (for PHP 7.0-7.3)

    • 3.0 or higher (for PHP 7.4 and higher)

  • re2c, which is used to generate the PHP lexer.

    • Optional for PHP <= 7.3.

    • 0.13.4 or higher (for PHP 7.4 and higher)

On Debian/Ubuntu you can install all these with the following command:

~/php-src> sudo apt-get install build-essential autoconf libtool bison re2c pkg-config

Depending on the extensions that you enable during the ./configure stage PHP will need a number of additional libraries. When installing these, check if there is a version of the package ending in -dev or -devel and install them instead. The packages without dev typically do not contain necessary header files. For example a default PHP build will require libxml and libsqlite3, which you can install via the libxml2-dev and libsqlite3-dev packages.

Build overview

Before taking a closer look at what the individual build steps do, here are the commands you need to execute for a “default” PHP build:

~/php-src> ./buildconf     # only necessary if building from git
~/php-src> ./configure
~/php-src> make -jN

For a fast build, replace N with the number of CPU cores you have available (you can run nproc to determine this).

By default PHP will build binaries for the CLI and CGI SAPIs, which will be located at sapi/cli/php and sapi/cgi/php-cgi respectively. To check that everything went well, try running sapi/cli/php -v.

Additionally you can run sudo make install to install PHP into /usr/local. The target directory can be changed by specifying a --prefix in the configuration stage:

~/php-src> ./configure --prefix=$HOME/myphp
~/php-src> make -jN
~/php-src> make install

Here $HOME/myphp is the installation location that will be used during the make install step. Note that installing PHP is not necessary, but can be convenient if you want to use your PHP build outside of extension development.

Now lets take a closer look at the individual build steps!

The ./buildconf script

If you are building from the git repository, the first thing you’ll have to do is run the ./buildconf script. This script does little more than invoking the build/ makefile, which in turn calls build/

The main job of these makefiles is to run autoconf to generate the ./configure script and autoheader to generate the main/ template. The latter file will be used by configure to generate the final configuration header file main/php_config.h.

Both utilities produce their results from the file (which specifies most of the PHP build process), the build/php.m4 file (which specifies a large number of PHP-specific M4 macros) and the config.m4 files of individual extensions and SAPIs (as well as a bunch of other m4 files).

The good news is that writing extensions or even doing core modifications will not require much interaction with the build system. You will have to write small config.m4 files later on, but those usually just use two or three of the high-level macros that build/php.m4 provides. As such we will not go into further detail here.

The ./buildconf script only has two options: --debug will disable warning suppression when calling autoconf and autoheader. Unless you want to work on the buildsystem, this option will be of little interest to you.

The second option is --force, which will allow running ./buildconf in release packages (e.g. if you downloaded the packaged source code and want to generate a new ./configure) and additionally clear the configuration caches config.cache and autom4te.cache/.

If you update your git repository using git pull (or some other command) and get weird errors during the make step, this usually means that something in the build configuration changed and you need to rerun ./buildconf.

The ./configure script

Once the ./configure script is generated you can make use of it to customize your PHP build. You can list all supported options using --help:

~/php-src> ./configure --help | less

The first part of the help will list various generic options, which are supported by all autoconf-based configuration scripts. One of them is the already mentioned --prefix=DIR, which changes the installation directory used by make install. Another useful option is -C, which will cache the result of various tests in the config.cache file and speed up subsequent ./configure calls. Using this option only makes sense once you already have a working build and want to quickly change between different configurations.

Apart from generic autoconf options there are also many settings specific to PHP. For example, you can choose which extensions and SAPIs should be compiled using the --enable-NAME and --disable-NAME switches. If the extension or SAPI has external dependencies you need to use --with-NAME and --without-NAME instead.

If a library needed by NAME is not located in the default location (e.g. because you compiled it yourself), some extensions allow you to specify its location using --with-NAME=DIR. However, since PHP 7.4 most extensions use pkg-config instead, in which case passing a directory to --with has no effect. In this case, it is necessary to add the library to the PKG_CONFIG_PATH:

export PKG_CONFIG_PATH=/path/to/library/lib/pkgconfig:$PKG_CONFIG_PATH

By default PHP will build the CLI and CGI SAPIs, as well as a number of extensions. You can find out which extensions your PHP binary contains using the -m option. For a default PHP 7.0 build the result will look as follows:

~/php-src> sapi/cli/php -m
[PHP Modules]

If you now wanted to stop compiling the CGI SAPI, as well as the tokenizer and sqlite3 extensions and instead enable opcache and gmp, the corresponding configure command would be:

~/php-src> ./configure --disable-cgi --disable-tokenizer --without-sqlite3 \
                       --enable-opcache --with-gmp

By default most extensions will be compiled statically, i.e. they will be part of the resulting binary. Only the opcache extension is shared by default, i.e. it will generate an shared object in the modules/ directory. You can compile other extensions into shared objects as well by writing --enable-NAME=shared or --with-NAME=shared (but not all extensions support this). We’ll talk about how to make use of shared extensions in the next section.

To find out which switch you need to use and whether an extension is enabled by default, check ./configure --help. If the switch is either --enable-NAME or --with-NAME it means that the extension is not compiled by default and needs to be explicitly enabled. --disable-NAME or --without-NAME on the other hand indicate an extension that is compiled by default, but can be explicitly disabled.

Some extensions are always compiled and can not be disabled. To create a build that only contains the minimal amount of extensions use the --disable-all option:

~/php-src> ./configure --disable-all && make -jN
~/php-src> sapi/cli/php -m
[PHP Modules]

The --disable-all option is very useful if you want a fast build and don’t need much functionality (e.g. when implementing language changes). For the smallest possible build you can additionally specify the --disable-cgi switch, so only the CLI binary is generated.

There are three more switches, which you should usually specify when developing extensions or working on PHP:

--enable-debug enables debug mode, which has multiple effects: Compilation will run with -g to generate debug symbols and additionally use the lowest optimization level -O0. This will make PHP a lot slower, but make debugging with tools like gdb more predictable. Furthermore debug mode defines the ZEND_DEBUG macro, which will enable the use of assertions and enable various debugging helpers in the engine. Among other things memory leaks, as well as incorrect use of some data structures, will be reported. It is possible to enable debug assertions without disabling optimizations by using --enable-debug-assertions instead.

--enable-zts (or --enable-maintainer-zts before PHP 8.0) enables thread-safety. This switch will define the ZTS macro, which in turn will enable the whole TSRM (thread-safe resource manager) machinery used by PHP. Since PHP 7 having this switch continuously enabled is much less important than on previous versions. It is primarily important to make sure you included all the necessary boilerplate code. If you need more information about thread safety and global memory management in PHP, you should read the globals management chapter

--enable-werror (since PHP 7.4) enables the -Werror compiler flag, which will promote compiler warnings to errors. Enabling this flag ensures that the PHP build remains warning free. However, generated warnings depend on the used compiler, version and optimization options, so some compilers may not be usable with option.

On the other hand you should not use the --enable-debug option if you want to perform performance benchmarks for your code. --enable-zts can also negatively impact runtime performance.

Note that --enable-debug and --enable-zts change the ABI of the PHP binary, e.g. by adding additional arguments to functions. As such, shared extensions compiled in debug mode will not be compatible with a PHP binary built in release mode. Similarly a thread-safe extension (ZTS) is not compatible with a non-thread-safe PHP build (NTS).

Due to the ABI incompatibility make install (and PECL install) will put shared extensions in different directories depending on these options:

  • $PREFIX/lib/php/extensions/no-debug-non-zts-API_NO for release builds without ZTS

  • $PREFIX/lib/php/extensions/debug-non-zts-API_NO for debug builds without ZTS

  • $PREFIX/lib/php/extensions/no-debug-zts-API_NO for release builds with ZTS

  • $PREFIX/lib/php/extensions/debug-zts-API_NO for debug builds with ZTS

The API_NO placeholder above refers to the ZEND_MODULE_API_NO and is just a date like 20100525, which is used for internal API versioning.

For most purposes the configuration switches described above should be sufficient, but of course ./configure provides many more options, which you’ll find described in the help.

Apart from passing options to configure, you can also specify a number of environment variables. Some of the more important ones are documented at the end of the configure help output (./configure --help | tail -25).

For example you can use CC to use a different compiler and CFLAGS to change the used compilation flags:

~/php-src> ./configure --disable-all CC=clang CFLAGS="-O3 -march=native"

In this configuration the build will make use of clang (instead of gcc) and use a very high optimization level (-O3 -march=native).

An option that is particularly useful for development is -fsanitize, which allows you to detect memory corruption and undefined behavior at runtime:

CFLAGS="-fsanitize=address -fsanitize=undefined"

These options only work reliably since PHP 7.4 and will significantly slow down the generated PHP binary.

make and make install

After everything is configured, you can use make to perform the actual compilation:

~/php-src> make -jN    # where N is the number of cores

The main result of this operation will be PHP binaries for the enabled SAPIs (by default sapi/cli/php and sapi/cgi/php-cgi), as well as shared extensions in the modules/ directory.

Now you can run make install to install PHP into /usr/local (default) or whatever directory you specified using the --prefix configure switch.

make install will do little more than copy a number of files to the new location. If you specified --with-pear during configuration, it will also download and install PEAR. Here is the resulting tree of a default PHP build:

> tree -L 3 -F ~/myphp

|-- bin
|   |-- pear*
|   |-- peardev*
|   |-- pecl*
|   |-- phar -> /home/myuser/myphp/bin/phar.phar*
|   |-- phar.phar*
|   |-- php*
|   |-- php-cgi*
|   |-- php-config*
|   `-- phpize*
|-- etc
|   `-- pear.conf
|-- include
|   `-- php
|       |-- ext/
|       |-- include/
|       |-- main/
|       |-- sapi/
|       |-- TSRM/
|       `-- Zend/
|-- lib
|   `-- php
|       |-- Archive/
|       |-- build/
|       |-- Console/
|       |-- data/
|       |-- doc/
|       |-- OS/
|       |-- PEAR/
|       |-- PEAR5.php
|       |-- pearcmd.php
|       |-- PEAR.php
|       |-- peclcmd.php
|       |-- Structures/
|       |-- System.php
|       |-- test/
|       `-- XML/
`-- php
    `-- man
        `-- man1/

A short overview of the directory structure:

  • bin/ contains the SAPI binaries (php and php-cgi), as well as the phpize and php-config scripts. It is also home to the various PEAR/PECL scripts.

  • etc/ contains configuration. Note that the default php.ini directory is not here.

  • include/php contains header files, which are needed to build additional extensions or embed PHP in custom software.

  • lib/php contains PEAR files. The lib/php/build directory includes files necessary for building extensions, e.g. the php.m4 file containing PHP’s M4 macros. If we had compiled any shared extensions those files would live in a subdirectory of lib/php/extensions.

  • php/man obviously contains man pages for the php command.

As already mentioned, the default php.ini location is not etc/. You can display the location using the --ini option of the PHP binary:

~/myphp/bin> ./php --ini
Configuration File (php.ini) Path: /home/myuser/myphp/lib
Loaded Configuration File:         (none)
Scan for additional .ini files in: (none)
Additional .ini files parsed:      (none)

As you can see the default php.ini directory is $PREFIX/lib (libdir) rather than $PREFIX/etc (sysconfdir). You can adjust the default php.ini location using the --with-config-file-path=PATH configure option.

Also note that make install will not create an ini file. If you want to make use of a php.ini file it is your responsibility to create one. For example you could copy the default development configuration:

~/myphp/bin> cp ~/php-src/php.ini-development ~/myphp/lib/php.ini
~/myphp/bin> ./php --ini
Configuration File (php.ini) Path: /home/myuser/myphp/lib
Loaded Configuration File:         /home/myuser/myphp/lib/php.ini
Scan for additional .ini files in: (none)
Additional .ini files parsed:      (none)

Apart from the PHP binaries the bin/ directory also contains two important scripts: phpize and php-config.

phpize is the equivalent of ./buildconf for extensions. It will copy various files from lib/php/build and invoke autoconf/autoheader. You will learn more about this tool in the next section.

php-config provides information about the configuration of the PHP build. Try it out:

~/myphp/bin> ./php-config
Usage: ./php-config [OPTION]
  --prefix            [/home/myuser/myphp]
  --includes          [-I/home/myuser/myphp/include/php -I/home/myuser/myphp/include/php/main -I/home/myuser/myphp/include/php/TSRM -I/home/myuser/myphp/include/php/Zend -I/home/myuser/myphp/include/php/ext -I/home/myuser/myphp/include/php/ext/date/lib]
  --ldflags           [ -L/usr/lib/i386-linux-gnu]
  --libs              [-lcrypt   -lresolv -lcrypt -lrt -lrt -lm -ldl -lnsl  -lxml2 -lxml2 -lxml2 -lcrypt -lxml2 -lxml2 -lxml2 -lcrypt ]
  --extension-dir     [/home/myuser/myphp/lib/php/extensions/debug-zts-20100525]
  --include-dir       [/home/myuser/myphp/include/php]
  --man-dir           [/home/myuser/myphp/php/man]
  --php-binary        [/home/myuser/myphp/bin/php]
  --php-sapis         [ cli cgi]
  --configure-options [--prefix=/home/myuser/myphp --enable-debug --enable-maintainer-zts]
  --version           [5.4.16-dev]
  --vernum            [50416]

The script is similar to the pkg-config script used by linux distributions. It is invoked during the extension build process to obtain information about compiler options and paths. You can also use it to quickly get information about your build, e.g. your configure options or the default extension directory. This information is also provided by ./php -i (phpinfo), but php-config provides it in a simpler form (which can be easily used by automated tools).

Running the test suite

If the make command finishes successfully, it will print a message encouraging you to run make test:

Build complete.
Don't forget to run 'make test'

make test will run the PHP CLI binary against our test suite, which is located in the different tests/ directories of the PHP source tree. As a default build is run against more than 10000 (less for a minimal build, more if you enable additional extensions) this can take several minutes.

The make test command internally invokes the run-tests.php file using your CLI binary. For more control, it is recommended to invoke run-tests.php directly. For example, this will allow you to enable the parallel test runner:

~/php-src> sapi/cli/php run-tests.php -jN

Test parallelism is only available as of PHP 7.4. On earlier PHP versions parallelism is not available, and it is necessary to additionally pass the -P option:

~/php-src> sapi/cli/php run-tests.php -P

Instead of running the whole test suite, you can also limit it to certain directories by passing them as arguments to run-tests.php. E.g. to test only the Zend engine, the reflection extension and the array functions:

~/php-src> sapi/cli/php run-tests.php -jN Zend/ ext/reflection/ ext/standard/tests/array/

This is very useful, because it allows you to quickly run only the parts of the test suite that are relevant to your changes. E.g. if you are doing language modifications you likely don’t care about the extension tests and only want to verify that the Zend engine is still working correctly.

You can run sapi/cli/php run-tests.php --help to display a full list of options the test runner accepts. Some particularly useful options are:

  • -c php.ini can be used to specify a php.ini file to use.

  • -d foo=bar can be used to set ini options.

  • -m runs tests under valgrind to detect memory errors. Note that this is extremely slow.

  • --asan should be set when compiling PHP with -fsanitize=address. Together these are approximately equivalent to running under valgrind, but with much better performance.

You don’t need to explicitly use run-tests.php to pass options or limit directories. Instead you can use the TESTS variable to pass additional arguments via make test. E.g. the equivalent of the previous command would be:

~/php-src> make test TESTS="-jN Zend/ ext/reflection/ ext/standard/tests/array/"

We will take a more detailed look at the run-tests.php system later, in particular also talk about how to write your own tests and how to debug test failures. See the dedicated tests chapter.

Fixing compilation problems and make clean

As you may know make performs an incremental build, i.e. it will not recompile all files, but only those .c files that changed since the last invocation. This is a great way to shorten build times, but it doesn’t always work well: For example, if you modify a structure in a header file, make will not automatically recompile all .c files making use of that header, thus leading to a broken build.

If you get odd errors while running make or the resulting binary is broken (e.g. if make test crashes it before it gets to run the first test), you should try to run make clean. This will delete all compiled objects, thus forcing the next make call to perform a full build. (You can use ccache to reduce the cost of rebuilds.)

Sometimes you also need to run make clean after changing ./configure options. If you only enable additional extensions an incremental build should be safe, but changing other options may require a full rebuild.

Another source of compilation issues is the modification of config.m4 files or other files that are part of the PHP build system. If such a file is changed, it is necessary to rerun the ./buildconf and ./configure scripts. If you do the modification yourself, you will likely remember to run the command, but if it happens as part of a git pull (or some other updating command) the issue might not be so obvious.

If you encounter any odd compilation problems that are not resolved by make clean, chances are that running ./buildconf will fix the issue. To avoid typing out the previous ./configure options afterwards, you can make use of the ./config.nice script (which contains your last ./configure call):

~/php-src> make clean
~/php-src> ./buildconf --force
~/php-src> ./config.nice
~/php-src> make -jN

One last cleaning script that PHP provides is ./vcsclean. This will only work if you checked out the source code from git. It effectively boils down to a call to git clean -X -f -d, which will remove all untracked files and directories that are ignored by git. You should use this with care.