Re: [PATCH 2/2] handle an unspecified return address column

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> Date: Tue, 26 Nov 2013 17:34:46 +0400
> From: Joel Brobecker <brobecker@adacore.com>
> 
> 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?

Please start with backing out the original change.