Stack unwind across signal frame

[Alan Cooper <alcooperx@gmail.com>]

I'm seeing a problem on both 2.6.37 and 3.3 MIPS kernels where I can't
unwind through a MIPS signal frame. It looks like this is caused by
the VDSO code that was added 2/2010. When the unwinder tries to find
the frame info for the caller of the signal handler (the trampoline in
VDSO), it can't find the eh_frame info because the address is in the
VDSO area and stops unwinding. It looks like other platforms solve
this by adding the eh_frame info for the VDSO area so the lookup
works.

This problem ends up breaking pthread cleanup for C++ programs because
the cleanup is done using a class with the expectation that the
destructor will be called when the thread gets canceled by a cancel
signal. This seems like a big problem for all current MIPS kernels so
I was wondering if I'm missing something?

If this is correct, then it seems like the best solution would be to
add the VDSO eh_frame info to MIPS.

Thanks
Al Cooper