On 06/19/2013 02:51 PM, Gedare Bloom wrote:
On Wed, Jun 19, 2013 at 3:22 AM, Sebastian Huber
<[email protected]> wrote:
>On 06/19/2013 01:54 AM, Chris Johns wrote:
>>
>>Sebastian Huber wrote:
>>>
>>>Some debuggers do not cope with the new DWARF3/4 debug format introduced
>>>with GCC 4.8. Default to strict DWARF-2 on ARM, PowerPC and SPARC for
>>>now.
>>>
>>>This patch should be committed to GCC 4.8 and 4.9.
>>>
>>
>>I am not convinced about this change on technical grounds. When I say I am
>>not
>>convinced, I am not sure what we gain and what we give up and I would like
>>to
>>understand that a little better before agreeing to it.
>>
>>I should also point out I am using ARM with gcc-4.8.1 and gdb-7.6 and it
>>is
>>working well (my OpenOCD changes need more work) and any change to DWARF2
>>that
>>alters this would be a regression.
>
>
>The recent ARM GDB seems to have no problem with the new debug format. I
>didn't see a differences in the debug experience between an old (e.g. 4.6.4)
>and a newer (e.g. 4.8.1) GCC. I didn't debug C++.
>
>
>>I have taken a look at the differences between DWARF2, DWARF3 and DWARF4.
>>There
>>is better language support in the later versions and debug data
>>compression.
>>These improvements are nice. What I am not sure about is the way limiting
>>gcc
>>to DWARF2 effects the debugging experience. If the flag is just a format
>>change
>>and the experience is the same that is ok, if however the C++ or C
>>debugging
>>experience is reduced that would be a regression.
>
>
>Yes, but I didn't see a difference so far. Debugging optimized code is
>still a pain.
>
>
>>My major concern is locking us into this and it being forgotten and we sit
>>on
>>DWARF2 for ages and we do not see or notice regressions related to
>>DWARF3/4
>>when it breaks on these archs. Can ARM/PowerPC/SPARC tools be built with a
>>target option that limits the target libraries to DWARF2 ?
>
>
>A compromise would be to apply this only to GCC 4.8. On PowerPC we have the
>situation that GCC 4.8 is the first version after 4.3 with all known bugs
>(bugs the render GCC useless and have no suitable workaround) fixed and no
>new ones (to our knowledge). It will take some time to upgrade the debug
>tools in running projects.
>
I'm fine with this compromise. If we apply it to gcc's development
head then we need to review the change periodically to determine if
DWARF 3/4 is ready to adopt for these couple of targets.
Chris pointed me to the undocumented CFLAGS_FOR_TARGET feature of GCC which is
supported by the RSB with the --targetcflags option. So you can build the
multilibs with special flags. I didn't test it yet, but I think this will make
the patch unnecessary.
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : [email protected]
PGP : Public key available on request.
Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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