Hi Tom,

On Wed, Nov 13, 2013 at 01:51:13PM -0700, Tom Tromey wrote:
> Debugging PR 16155 further, I found that the DWARF unwinder found the
> function in question, but thought it had no registers saved
> (fs->regs.num_regs == 0).
> 
> It seems to me that if a frame does not specify the return address
> column, or if the return address column is explicitly marked as
> DWARF2_FRAME_REG_UNSPECIFIED, then we should set the
> "undefined_retaddr" flag and let the DWARF unwinder gracefully stop.
> 
> This patch implements that idea.
> 
> With this patch the backtrace works properly:
> 
>     (gdb) bt
>     #0  0x0000007fb7ed485c in nanosleep () from /lib64/libc.so.6
>     #1  0x0000007fb7ed4508 in sleep () from /lib64/libc.so.6
>     #2  0x00000000004008bc in thread_function (arg=0x4) at threadapply.c:73
>     #3  0x0000007fb7fad950 in start_thread () from /lib64/libpthread.so.0
>     #4  0x0000007fb7f0956c in clone () from /lib64/libc.so.6
> 
> 2013-11-13  Tom Tromey  <tromey@redhat.com>
> 
> 	PR backtrace/16155:
> 	* dwarf2-frame.c (dwarf2_frame_cache): Set undefined_retaddr if
> 	the return address column is unspecified.

I just found out that this patch causes some problems on at least
arm-elf and ppc-elf. Attached is a proposed patch, with associated
analysis.

gdb/ChangeLog:

        PR backtrace/16155:
        * dwarf2-frame.c (dwarf2_frame_cache): Remove condition that
        sets cache->undefined_retaddr to 1 if there is no column in
        the frame info for the return register.

Tested on x86_64-linux, no regression. It also fixes all regressions
observed on arm-elf and ppc-elf.

Can you tell me what you think?

Thank you!
-- 
Joel