Comment 4 for bug 1094950

Just a note that IME trying to debug QEMU under gdb on MacOS doesn't work very well. In particular as far as I can tell gdb breaks sigwait() such that the sigwait() in sigwait_compat() can return 0 without setting the int* sig. This causes QEMU to write an uninitialized value into the qemu_signalfd_siginfo struct it sends down the pipe, and then sigfd_handler() calls sigaction() with this bogus data as the signal number. Since sigfd_handler() doesn't check the return value from sigaction() we then proceed to leap off into nowhere.

sigfd_handler() should probably be checking the return value from sigaction() but the underlying problem is MacOS and/or its gdb breaking sigwait() behaviour somehow.