Image format detection false positives with external GD

[orlitzky]

Description

To check for supported image types, PHP (ext/gd/config.m4) tries to link against libgd:

AC_DEFUN([PHP_GD_CHECK_VERSION],[
  PHP_CHECK_LIBRARY(gd, gdImageCreateFromPng,          [AC_DEFINE(HAVE_GD_PNG,               1, [ ])], [], [ $GD_SHARED_LIBADD ])
  PHP_CHECK_LIBRARY(gd, gdImageCreateFromAvif,         [AC_DEFINE(HAVE_GD_AVIF,              1, [ ])], [], [ $GD_SHARED_LIBADD ])
  ...
])

However, upstream libgd declares those functions unconditionally. Using AVIF as an example, gdImageCreateFromAvif is declared unconditionally at https://github.com/libgd/libgd/blob/master/src/gd.h#L683, and then implemented (when AVIF support is disabled) in https://github.com/libgd/libgd/blob/master/src/gd_avif.c#L674. As a result, PHP decides that it supports AVIF images when it does not.

In particular this causes imagetypes() to return types that PHP does not actually support. It also results in several PHP functions being made available that should not be, e.g.

#ifdef HAVE_GD_AVIF
/* {{{ Create a new image from AVIF file or URL */
PHP_FUNCTION(imagecreatefromavif)
{
        _php_image_create_from(INTERNAL_FUNCTION_PARAM_PASSTHRU, PHP_GDIMG_TYPE_AVIF, "AVIF", gdImageCreateFromAvif, gdImageCreateFromAvifCtx);
}
/* }}} */
#endif /* HAVE_GD_AVIF */

Finally, those two issues lead to test failures when format-specific are not skipped as they should be:

$ head ./ext/gd/tests/imagecreatefromstring_avif.phpt 
--TEST--
imagecreatefromstring() - AVIF format
--EXTENSIONS--
gd
--SKIPIF--
<?php
if (!(imagetypes() & IMG_AVIF)) {
    die('skip AVIF support required');
}
?>

Thus when some formats are missing from the system gd, there are a few more test failures to add to the list in #11252

PHP Version

git head

Operating System

No response

[orlitzky]

When freetype support is missing from gd, PHP actually fails to build. The feature detection looks for a function that's always there, but then PHP tries to call a function that is only defined conditionally:

/var/lib/portage/tmp/portage/dev-lang/php-8.2.9/work/sapis-build/cli/ext/gd/gd.c:369: undefined reference to `gdFontCacheShutdown'
collect2: error: ld returned 1 exit status
make: *** [Makefile:264: sapi/cli/php] Error 1

[andypost]

Thank you! it helps #7526

[rs-bc]

This breaks detection of libgd supported graphic formats completely on a FreeBSD-13.2 system:

configure:37620: checking for working gdImageCreateFromWebp in libgd
configure:37655: cc -o conftest -g -O2 -fvisibility=hidden -D_GNU_SOURCE -Wl,-rpath,/usr/local/lib -L/usr/local/lib conftest.c -lutil -lrt -lm -lxml2 -Wl,-rpath,/usr/local/lib -L/usr/local/lib -lgd >&5
conftest.c:250:10: fatal error: 'gd.h' file not found
#include <gd.h>

/usr/local/include is missing from the include path!

[orlitzky]

This breaks detection of libgd supported graphic formats completely on a FreeBSD-13.2 system:

configure:37620: checking for working gdImageCreateFromWebp in libgd configure:37655: cc -o conftest -g -O2 -fvisibility=hidden -D_GNU_SOURCE -Wl,-rpath,/usr/local/lib -L/usr/local/lib conftest.c -lutil -lrt -lm -lxml2 -Wl,-rpath,/usr/local/lib -L/usr/local/lib -lgd >&5 conftest.c:250:10: fatal error: 'gd.h' file not found #include <gd.h>

/usr/local/include is missing from the include path!

PHP itself tries to #include <gd.h> in ext/gd/gd.c, so if it isn't in your include path, then the system copy of gd won't be usable.

Are you somehow adding it to your include path after ./configure? We should probably reject the system gd entirely if gd.h isn't found, but it would be nice to understand how this used to work for you first.

[rs-bc]

PHP-8.3.2 compiles fine with external libgd.
GDLIB_CFLAGS are populated correctly for php-8.3.2 and php-8.3.4 in config.log.

The problem here is the test code, which tries to include gd.h without properly set include path (despite having set a correct library path).

[orlitzky]

It would be helpful to know what

$ pkg-config --cflags gdlib

returns on this system. I'm starting to suspect that,

PKG_CHECK_MODULES([GDLIB], [gdlib >= 2.1.0])
PHP_EVAL_LIBLINE($GDLIB_LIBS, GD_SHARED_LIBADD)
PHP_EVAL_INCLINE($GDLIB_CFLAGS)
AC_DEFINE(HAVE_LIBGD, 1, [ ])
PHP_GD_CHECK_VERSION

doesn't actually add GDLIB_CFLAGS to CFLAGS (or CPPFLAGS), in which case we just have to add them to the format check explicitly.

[rs-bc]

$ pkg-config --cflags gdlib
-I/usr/local/include -I/usr/local/include/webp -I/usr/local/include/freetype2 -I/usr/local/include/libpng16

[orlitzky]

PHP-8.3.2 compiles fine with external libgd. GDLIB_CFLAGS are populated correctly for php-8.3.2 and php-8.3.4 in config.log.

Ok, thanks, my mistake then. I thought the GDLIB_CFLAGS were added at that point. I'll fix it when I get to work.

[petk]

Probably something like this needs to be done in ext/gd/config.m4 at that check:

    CFLAGS_save="$CFLAGS"
    CFLAGS="$INCLUDES $CFLAGS"
    ... 
    CFLAGS="$CFLAGS_save"

[orlitzky]

Ok, please test if you can: #13724