Back in Leopard days, I was playing with the x86-64 ABI on Mac OS X (no real documentation existed whatsoever, or at least that I could find, except for the sou

Back in Leopard days, I was playing with the x86-64 ABI on Mac OS X (no real documentation existed whatsoever, or at least that I could find, except for the source code). Very soon I accidentally ran into a kernel panic that could be reduced to a three-instruction program: mov rax, 1 mov rdi, 1 syscall and it would bring down the entire OS (kernel panic) when run by any user mode application under a standard non-root user. Took a few releases for them to fix that. I stopped trusting them from a low-level reliability perspective since then. Fuzzing their system call interface may not have been a bad idea. P.S. XNU is an interesting as it lets userspace use Mach syscalls as well as a bunch of BSD system calls directly. Probably esoteric interactions between them are not very well-thought-out. (I hope I am not offending Avie Tevanian here :))