On Wed, Mar 12, 2014 at 8:33 AM, Peng Yuan <yingbo....@gmail.com> wrote: > > I'm using backtrace() to obtain call context by sending signals. But > program segfaults if the first instruction of a function receives > signal for backtrace. > > ARM unwinding in libgcc uses "return_address -= 2" to get the caller > address. It is OK for normal function call with "bl xxx". But it > cannot handle signal frame case because "return_address -= 2" may go > to the preceding function. > See get_eit_entry() in libgcc/unwind-arm-common.inc. > > Both GDB and libunwind take signal frame as a special case on ARM > unwinding. Does libgcc also need to fix the case?
Note that the default libgcc unwinder does support special handling of signal frames. See _Unwind_IsSignalFrame and _Unwind_SetSignalFrame and the signal_frame field of _Unwind_FrameState. The signal_frame is set by, for example, x86_64_fallback_frame_state in gcc/config/linux/linux-unwind.h. So clearly something similar can be done for ARM. My understanding is that the ARM EABI specifies the unwind info. I don't know how that would affect this idea. Ian
