Patch: Fix signal handlers under indirect-dispatch on MIPS

[Andrew Haley]

David Daney writes:
 > For some (as yet unknown) reason on MIPS with -findirect-dispatch, the 
 > SIGSEGV and SIGFPE signal handlers were not being installed properly. 
 > This caused the failure of any test case that triggered an 
 > ArithmeticException or NullPointerException via the signal handling 
 > mechanism.

Perhaps the shape of your struct kernel_sigaction was wrong.

 > The fix is to call libc's sigaction function instead of trying to trick 
 > libc by doing a direct system call to the kernel.  Since the MIPS port 
 > does not need to patch-up and restart any faulting divide instructions, 
 > the syscall trick is not needed.  This has the added benefit of slightly 
 > simplifying the code.
 > 
 > I guess it is not nice to trick glibc...

The other reason I did this with a direct syscall rather than a libc
call was that libc didn't used to be compiled with unwind information,
so it wasn't possible to unwind through its handlers.

Andrew.