Blair Barnett writes: > We're using the EABI extensions, so I think we're safe there. We're > trying the patch now. However, being unfamiliar with this code, I'm > wondering how it works, since I don't see any calls to the new > functions in the patch: > http://gcc.gnu.org/ml/gcc-patches/2007-08/msg01388.html > > Thanks for all the help! There may be light at the end of this tunnel! For _Unwind_Backtrace to work, all code must be compiled with -fexceptions. Also, if you want to unwind through a signal handler you'll need some code that recognizes a signal frame and unwinds through it. There is not yet any such thing for ARM EABI. There's an example of how you do this at x86_64_fallback_frame_state() in gcc/config/i386/linux-unwind.h. This kind of thing is hard to write: I understand exactly how it all works, and it would take me quite a while to figure out how to load the _Unwind_Context from the sigcontext. Andrew. > ----- Original Message ---- > From: Andrew Haley <aph-gcc@xxxxxxxxxxxxxxxxxxx> > To: Blair Barnett <blairbarnett@xxxxxxxxxxxxx> > Cc: gcc-help mailing list <gcc-help@xxxxxxxxxxx> > Sent: Wednesday, August 29, 2007 11:00:43 AM > Subject: Re: Solution sought to GCC 4.1.1 backtrace problem > > Backtracing through segfaults is hard. The approach we use in > glibc/GNU/Linux is a function called *_fallback_frame_state, which > copies the saved registers on the stack into the unwinder data. > However, this only works if you're using DWARF-style unwinder data, > which is used in the EABI port of ARM. > > If you're not using EABI, you really need to write your own version of > backtrace() that starts from a signal fram and unwinds through it. > The SIGCONTEXT ctx that's passed to your segfault handler contains the > registers at the point the segfault occurred, and you can unwind > starting from there. > > Don't do this: > > void *fp = __builtin_frame_address (0); > > Instead, pull fp and sp out of the SIGCONTEXT ctx. > > Andrew. > > >
