Stepping out of signal handler problem

[Mark Kettenis]

> From: Aleksandar Ristovski <aristovski@qnx.com>
> Date:  Fri, 16 May 2008 12:26:43 -0400
>
> This makes question 2: Is the only way to implement this similar to
> linux-nat (scanning for sigreturn kernel call)? Is there anything
> 'cleaner'?

The clean way of doing this is provide proper unwind info for the
signal trampoline.  This shouldn't be too difficult if your signal
trampolines live in libc, and quite a bit harder if they are in the
kernel.