The same way any decompilation works - By looking at patterns, understanding how the original compiler worked, and following the execution path as it runs. Antimalware analysts have been doing far more complex for many years, including packed, encrypted, and self-modifying code. It temporarily obfuscates what's going on, but execution tells all. Not that you'd need anything that advanced, when you have the source code and can compare possible fuzzed outputs.

ASLR is a real technique that can make targets harder to pop on the first try, giving you time to detect the problem. It does not prevent bugs from being exploited, at least not reliably and for long. This is not a real security topic, this is minor roadbumps, urban myth, and quackery.