ARM Linux EABI: unwinding through a segfault handler

[Ken Werner]

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. :)

Regards
Ken