Description:
------------
Using recursive functions for preg_replace_callback that never ends PHP will exit with a SEGFAULT (unexpected signal 11) due to a function stack overflow.

It's expected that it should never end and therefore PHP should abort the execution. However PHP should output a helpful error message rather than just aborting it. Depending on your code this could be a major issue to debug. (I was using Drupal and it look me hours to find the source.)

Test script:
---------------
<?php

function a() {
  b();
}
function b() {
  a();
}

preg_replace_callback("/0/s", 'a', "0");
echo "We made it my friend!";


Expected result:
----------------
Some sort of error message that the callback stack limit has been reached.

Actual result:
--------------
A 500 Internal Server error (Apache with mod_fcgid) and a SEGFAULT in the error log.