Re: Follow up to stabs deprecation - AIX regressions

[Guinevere Larsen <guinevere@redhat.com>]

On 2/13/25 5:21 PM, Simon Marchi wrote:
>
> On 2025-02-13 12:58, Guinevere Larsen wrote:
>> On 2/13/25 2:43 PM, Kevin Buettner wrote:
>>> On Thu, 13 Feb 2025 14:21:01 -0300
>>> Guinevere Larsen <guinevere@redhat.com> wrote:
>>>
>>>> On 2/13/25 1:48 PM, Kevin Buettner wrote:
>>>>> On Thu, 13 Feb 2025 09:25:44 -0300
>>>>> Guinevere Larsen <guinevere@redhat.com> wrote:
>>>>>   
>>>>>> * DWARF reading can sometimes fail in AIX. Currently, reading dwarf for
>>>>>> xcoff inferiors is called on it's own, with no warning if dwarf fails
>>>>>> (which probably makes sense, considering the default format in aix is
>>>>>> still stabs). I added a warning when failing to read dwarf and noticed
>>>>>> it being triggered on inferiors compiled with -gdwarf
>>>>> I assume that you mean that stabs is the default when compiling with
>>>>> gcc.  Is stabs still also the default format for XLC (IBM Open XL C/C++) ?
>>>> Yes, sorry, I meant gcc. The compile farm had versions 10 and 12, both
>>>> with the same behavior.
>>>>
>>>> I don't think the compile farm has XLC compilers available for testing,
>>>> or if they do I don't know how to use it, so I couldn't tell you...
>>> I think it'd be good to find out XLC's preferred debug format.  If it
>>> uses/prefers DWARF, that'd be a good argument for gcc (on AIX)
>>> switching to DWARF for it's preferred format too.
>>>
>>> Kevin
>>>
>> I just looked over at the GCC releases, and the GCC12 changelog says the following:
>>
>>    * *STABS:* Support for emitting the STABS debugging format is deprecated and will be removed in the next release. All ports now default to emit DWARF (version 2 or later) debugging info or are obsoleted.
>>
>> Since the default is supposed to have changed *in* gcc 12 - which is the version that AIX has - or the port be obsolete, it looks to me like that gcc on AIX is obsoleted...
>>
>> In other words, gcc already knows it should change but seems to have given up on AIX?
> Given this commit (present in gcc 11):
>
> https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=56b5d13e27891ed1caec07826a07bb2e0621f914
>
> I would expect gcc 12 to produce DWARF by default, I'm not sure why you
> don't see that.
>
> Simon
>
This is kind of weird...

This is a bit of a side diversion, though. The original thing Kevin 
pointed out was whether GDB not reporting that DWARF reading failed was 
related to stabs being the default.

I just double checked, and I don't think it is. elfread reads dwarf in 
an if condition, but doesn't do anything with the result (no matter if 
it is positive or negative). coffread does the same

I think the idea is that maybe the objfile being read may have not been 
compiled with debug symbols in the first place, so warning about it is 
redundant, especially considering that for now, all supported objfiles 
will have at least minsyms available. That will change with removing 
stabs in xcoff, which is why I highlighted that it can fail even with 
existing dwarf in the inferior. It not being reported is the default, 
but is why this has gone unnoticed.

-- 
Cheers,
Guinevere Larsen
She/Her/Hers