On 08/29/2011 06:13 PM, Daniel Jacobowitz wrote: > On Mon, Aug 29, 2011 at 11:18 AM, Ken Werner <ken.wer...@linaro.org> wrote: >> On 08/25/2011 02:26 PM, Andrew Haley wrote: >>> >>> Throwing an exception through a segfault handler doesn't always work >>> on ARM: the attached example fails on current gcc trunk. >>> >>> panda-9:~ $ g++ segv.cc -fnon-call-exceptions -g >>> panda-9:~ $ ./a.out >>> terminate called after throwing an instance of 'FoobarException*' >>> Aborted >>> >>> The bug is that _Unwind_GetIPInfo doesn't correctly set ip_before_insn. >>> Instead, it always sets it to zero; it should be set to 1 if this >>> is a frame created by a signal handler: >>> >>> >>> #define _Unwind_GetIPInfo(context, ip_before_insn) \ >>> (*ip_before_insn = 0, _Unwind_GetGR (context, 15)& ~(_Unwind_Word)1) >>> >>> >>> Fixing this on ARM is hard because signal frames aren't specially >>> marked as they are on systems that use DWARF unwinder data. I have >>> a patch that works on systems where the signal restorer is exactly >>> >>> mov r7, $SYS_rt_sigreturn >>> swi 0x0 >>> >>> It works as a proof of concept, but it's fugly. >>> >>> So, suggestions welcome. Is there a nice way to detect a signal frame? >> >> Libunwind also reads the IP to detect signal frames on ARM Linux: >> http://git.savannah.gnu.org/gitweb/?p=libunwind.git;a=blob;f=src/arm/Gis_signal_frame.c;hb=HEAD >> >> I'd also be interested if there are better approaches to detect them. :) > > There aren't better ways - this is pretty much the standard for > on-stack signal frames :-) > > I thought we used a handler in GLIBC that was properly annotated, > nowadays, but I might be mistaken.
We don't for ARM, and indeed we can't. ARM unwind frames don't have any way of encoding the fact that they're signal frames or AFAICS of encoding the return address offset. Andrew.
