How to compile AFL's LLVM mode in OS X

American fuzzy lop aka AFL is one of the easiest and best fuzzers out there and should be part of your development cycle if you care at least one bit about the security of your code.

Its performance in OS X is a bit of a let down because of issues at fork() system call. AFL warns you about this when compiling it:

WARNING: Fuzzing on MacOS X is slow because of the unusually high overhead of fork() on this OS. Consider using Linux or *BSD. You can also use VirtualBox ( to put AFL inside a Linux or *BSD VM.

[Read More]