On 08/25/2011 05:26 AM, 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.
For what it's worth, I did the equivalent on MIPS.
Once you do this, it is a de facto ABI. Probably the ARM linux
maintainers should be consulted to see if they are willing to consider
the possibility of never changing it.
I think all Linux ABIs should support unwinding through signal handlers,
so adding this makes sense to me.
David Daney
So, suggestions welcome. Is there a nice way to detect a signal frame?
