I've got the core of the parrot interpreter working. It's not that fancy, does no I/O other than a few printf/puts in some debugging ops, and has a makefile that's pathetically simple. The thing even builds and runs on both Linux and VMS.
The same code, when built on FreeBSD (cleanly I might add), bus errors and cores. Do one malloc and Bam! it dies.
(Though the interpreter's more complex now--it can load in bytecode that's been frozen to disk. A quick mmap() and there ya go. I'm sure this won't build anywhere but my development machine, for sheer mmap reasons if nothing else, but that at least is okay, since I'm expecting that)