David Daney writes:
> With the current kernel (18.104.22.168) in my R5000 based O2 it seems
> impossible for GCC's exception unwinding machinery to unwind through
> signal frames. The cause of the problems is the
> ICACHE_REFILLS_WORKAROUND_WAR which puts the sigcontext at an almost
> impossible to determine offset from the signal return trampoline. The
> unwinder depends on being able to find the sigcontext given a known
> location of the trampoline.
> It seems there are a couple of possible solutions:
> 1) The comments in war.h indicate the problem only exists in R7000
> and E9000 processors. We could turn off the workaround if the
> kernel is configured for R5000. That would help me, but not those
> with the effected systems.
> 2) In the non-workaround case, the siginfo immediately follows the
> trampoline and the first member is the signal number. For the
> workaround case the first word following the trampoline is zero.
> We could replace this with the offset to the sigcontext which is
> always a small negative value. The unwinder could then distinguish
> the two cases (signal numbers are positive and the offset
> negative). If we did this, the change would have to be coordinated
> with GCC's unwinder (in libgcc_s.so.1).
The best solution is to put the unwinder info in the kernel. Does
MIPS use a vDSO ?