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

[Sebastian Huber]

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.

>
> 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

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