[Libunwind-devel] SIGFPE and _Unwind_GetIPInfo problem on x86_64 (g++-4.5)

[address@hidden]

Hi,

I've experimented somewhat with throwing exceptions from within a signal 
handler.
Libunwind seems to work in the case of SIGILL, SIGBUS, SIGSEGV, but not always 
for SIGFPE.

The attached program shall demonstrate a failing SIGFPE-case
(sigfpe.sh contains all necessary steps to demonstrate this).

The program runs successfully if you use the default gcc unwinding routines,
but it crashes, if you preload libunwind. The only difference between
gcc and libunwind seems to be the returned flag `ip_before_ins`
when calling _Unwind_GetIPInfo. This is also shown in the test program.

As far as I can tell the following happens (See attached backtrace and output):
- personality routine is called for sighandler()-frame (#0)
- libunwind identifies a signal stack frame (with no personality routine) (#1)
- personality routine is called for fpe()-frame (#2)
  Here _Unwind_GetIPInfo returns 0 for ip_before_ins because this frame
  is identified as a regular frame.

As I'm not an expert on that unwinding stuff, maybe somebody else on this list
can explain, why this happens - Is it a feature of gcc or a bug in libunwind? :)

Regards
Stefan

bt_and_example_output.txt
Description: Text document

sigfpe.cpp
Description: Text Data

sigfpe.sh
Description: Bourne shell script