I'm working on a native PHP extension which includes symbols from a shared library, but I can't get the `config.m4` file to generate a build procedure that includes the necessary linker options to correctly link to the share library. This is what I have in my `config.m4` file so far:

```
PHP_ARG_ENABLE(myextension, whether to enable MyExtension support, [ --enable-myextension   Enable MyExtension support])

if test "$PHP_MYEXTENSION" = "yes"; then

  LIBNAME=otherlibrary
  LIBSYMBOL=otherlib_some_function
  LIBOTHERLIB_LIBS=`pkg-config --libs otherlibrary`
  LIBOTHERLIB_INC=`pkg-config --cflags otherlibrary`

  PHP_CHECK_LIBRARY($LIBNAME,$LIBSYMBOL,
  [
    PHP_EVAL_INCLINE($LIBOTHERLIB_INC)
    PHP_EVAL_LIBLINE($LIBOTHERLIB_LIBS)
    AC_DEFINE(HAVE_MYEXTENSION, 1, [Whether you have MyExtension])
  ],[
    AC_MSG_ERROR([wrong lib$LIBNAME version or library not found])
  ])

  PHP_NEW_EXTENSION(myextension, myextension.c, $ext_shared)
fi

```

The `libotherlibrary` library is in a standard system location. When I `phpize` with this configuration and then execute the generated `configure` script with the `--enable-myextension` argument it successfully generates a `Makefile` etc. and I can see it doing the test for `otherlib_some_function` from `libotherlibrary` which passes. But calling `ldd` on my resulting myextension.so gives just:

```
linux-vdso.so.1 (0x00007ffd11fce000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f741e653000)
/lib64/ld-linux-x86-64.so.2 (0x00007f741ec26000)

```

so no mention of `libotherlibrary`. And the `libtool` and `cc` commands which are executed by the `Makefile` don't include the `-lotherlibrary` option. And then when I try and execute a PHP script which uses my extension I get:

```
php: symbol lookup error: /path/to/modules/myext.so: undefined symbol: otherlib_some_function

```

In place of `PHP_EVAL_INCLINE` and `PHP_EVAL_LIBLINE` I've also tried the `PHP_ADD_LIBRARY` macro:

```
PHP_ADD_LIBRARY($LIBNAME,,OTHERLIB_SHARED_LIBADD)

```

(I don't understand what the third argument to this macro is for.)

I've also tried (in combination with both of the above), including the fifth argument to `PHP_CHECK_LIBRARY` called `extra-libs` passing in the value of my `$LIBOTHERLIB_LIBS` variable. Doing so doesn't fix anything, and there's no documentation of what this argument is supposed to do or what values it requires. So this is just a guess really.

So how can I get my extension to build with the required `-lotherlibrary` linker option?