Hmm. Is the third argument to my SA_SIGINFO signal handler a pointer to a ucontext?
According to gdb, it's 0x0. This isn't likely to be good. My code works as expected on x86 and ppc, so I think I'm going to blame the sparc64 kernel. Grr.
Oh well. Time to branch out into other SBCL improvements anyway. Vectorizing lisp compilers, here we come!