Actually, before LLVM bitcode, self-checksumming was quite possible on iOS, and is widely used by many commercial obfuscators. Furthermore, self-checksumming is

Actually, before LLVM bitcode, self-checksumming was quite possible on iOS, and is widely used by many commercial obfuscators. Furthermore, self-checksumming is the root of all good anti-tamper schemes. It prevents someone from automatically patching out your license checks/anti debug/anti jailbreak/whatever. Without self-checksumming, someone can easily patch your app to pirate it, inject a backdoor, or modify it in some unwanted way. So it's really a big loss if you care about those kinds of things. Self-checksumming via intrinsics and clever layouts is a very interesting idea, but it's impossible for you to checksum a program when you're not 100% sure what it will look like after compilation. For example, even if you manage to correctly 'guess' what machine code your LLVM bitcode would be translated to and adjusted your checksums accordingly, Apple could just update their LLVM bitcode compiler at some point in the future, and invalidate your checksums. Also Android is a much more interesting platform than iOS, because it allows for self-modifying code, which various commercial obfuscators use in various interesting ways :) Also there are very interesting things you can do with reflection or the JNI in Java.