On Tue, Nov 13, 2007 at 11:48:53AM +0000, Andrew Haley wrote: > David Daney writes: > > With the current kernel (2.6.23.1) 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). > > > > Thoughts? > > The best solution is to put the unwinder info in the kernel. Does > MIPS use a vDSO ? No though we should. Another reason is to get rid of the classic trampoline the kernel installs on the stack. On some multiprocessor systems it requires a cacheflush operation to be performed on all processors which is expensive. Having the trampoline in a vDSO would solve that. I need to look into it, not sure what it would take. Ralf
