Derick Rethans has shared a quick tip for locating a code crashing kind of problem with your application when something like XDebug isn't around.
However, because we as PHP developers are lazy, provide a few GDB tricks to make this easier. First of all, it's only really going to work if you haven't stripped the symbols from your PHP and Apache binaries. Secondly, you still need to have the PHP source lying around somewhere.
He suggests using GDB to run the backtraces and create a file to help you track down the infinite recursion problem that could be giving you issues.