writing php extension that uses external shared library - php

Question

I have difficulty trying to write a php extension that uses an external shared library:
The content of config.m4 is as follows:
PHP_ARG_WITH([foo],
[for foo support],
[AS_HELP_STRING([--with-foo],
[Include foo support])])
if test "$PHP_FOO" != "no"; then
PKG_CHECK_MODULES([LIBFREETYPE2], [freetype2 >= 23.4.17])
PHP_EVAL_INCLINE($LIBFREETYPE2_CFLAGS)
PHP_EVAL_LIBLINE($LIBFREETYPE2_LIBS, FOO_SHARED_LIBADD)
PHP_NEW_EXTENSION(foo, foo.c, $ext_shared)
fi
The code of the main function in foo.c is as follows(Just a very simple example of using the external FreeType library):
PHP_FUNCTION(foo_test) {
ZEND_PARSE_PARAMETERS_NONE();
FT_Library ft;
if (FT_Init_FreeType(&ft)) {
php_printf("FreeType library failed to load\n");
return;
}
php_printf("FreeType library successfully loaded\n");
FT_Done_Library(ft);
php_printf("FreeType library unloaded\n");
}
phpize, ./configure, make and make install all succeeded, and then I added the extension in php.ini:
extension = foo.so
So far so good, but then I ran the following command
echo "<?php foo_test();" | php
I got the following error message:
php: symbol lookup error: /the-path-of-foo/foo.so: undefined symbol:
FT_Init_FreeType
It looks like PHP doesn't load the external shared FreeType library my PHP extension intends to use.
How do I do to make PHP load the external shared FreeType library?
Thanks for help.

Answer 1

Resolved this issue by adding PHP_SUBST(FOO_SHARED_LIBADD) after PHP_EVAL_LIBLINE($LIBFREETYPE2_LIBS, FOO_SHARED_LIBADD):
PHP_ARG_WITH([foo],
[for foo support],
[AS_HELP_STRING([--with-foo],
[Include foo support])])
if test "$PHP_FOO" != "no"; then
PKG_CHECK_MODULES([LIBFREETYPE2], [freetype2 >= 23.4.17])
PHP_EVAL_INCLINE($LIBFREETYPE2_CFLAGS)
PHP_EVAL_LIBLINE($LIBFREETYPE2_LIBS, FOO_SHARED_LIBADD)
PHP_SUBST(FOO_SHARED_LIBADD)
PHP_NEW_EXTENSION(foo, foo.c, $ext_shared)
fi

Answer 2

Your config.m4 shoud be like
...
PHP_EVAL_LIBLINE($LIBFREETYPE2_LIBS, EXTRA_CFLAGS)
PHP_SUBST(EXTRA_CFLAGS)
PHP_NEW_EXTENSION(foo, foo.c, $ext_shared)
fi