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. -- Thanks, Daniel
