[PATCH] RTEMS: Use strict DWARF-2 on ARM, PowerPC, SPARC

[Gedare Bloom]

On Wed, Jun 19, 2013 at 3:22 AM, Sebastian Huber
<sebastian.huber at embedded-brains.de> 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.

>
>>
>> Did a gdb bug get raised about the DWARF read error reported on the
>> mailing list ?
>
>
> No, I had no time to investigate this further.
>
>
> --
> Sebastian Huber, embedded brains GmbH
>
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> Phone   : +49 89 189 47 41-16
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> E-Mail  : sebastian.huber at embedded-brains.de
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>
> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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