[libcamera-devel] [PATCH 2/4] meson: enable no-psabi for gcc 9+

[Kieran Bingham]

Hi Laurent,

On 12/10/2020 00:52, Laurent Pinchart wrote:
> Hi Tomi,
> 
> On Fri, Oct 09, 2020 at 10:03:39AM +0300, Tomi Valkeinen wrote:
>> On 09/10/2020 04:37, Laurent Pinchart wrote:
>>
>>>> I don't think I get this whole thing =). But I'm fine with increasing
>>>> the version check to < 10, as I'm currently using gcc 9. I'll probably
>>>> switch my buildroot to gcc 10 at some point in the near future, and
>>>> then I can send a new patch.
>>>
>>> The idea is that I'd like to keep an eye on ABI breakages introduced by
>>> gcc, in a "just for my information" fashion for the moment. I don't know
>>> at this point how such breakages would even be handled (if at all).
>>>
>>> "Just for my information" is probably not a good enough excuse to annoy
>>> everybody with warnings when using new compiler versions though. I'd
>>> thus agree to drop the version check. I wonder how the gcc developers
>>> had envisioned this being used though, if there's a warning (which is
>>> actually not even a warning, but a note), I imagine it was put there
>>> with a target audience in mind. Or maybe this is just a mess and nobody
>>> should really pay attention :-)
>>
>> Ok. Yes, I don't get this either. What would make sense is, e.g.
>> "-Wno-psabi=1,4", which would disable warnings for ABI breakages #1
>> and #4, but allow all the other warnings.
>>
>> What I did in kms++ was just:
>>
>> if (cpp.get_id() == 'gcc' and
>>     host_machine.cpu_family() == 'arm' and
>>     cpp.has_argument('-Wno-psabi'))
>>
>>     cpp_arguments += [
>>         '-Wno-psabi',
>>     ]
>> endif
>>
>> It's silly to always disable the warning, but I haven't found much
>> info about it while googling, so currently I'm guessing it's the "this
>> is just a mess" case.
> 
> I think I'm getting convinced that this is indeed the right way forward
> for now. Kieran, what do you think ?

The part of all this that I don't like is that GCC doesn't (seem to)
have a way to disable (/acknowledge) the ABI change from v7, to ignore
'just that set'.

So indeed, it means that these warnings will currently persist forever -
and then get blurred in with any additional ones. Which is quite
frustrating.

Along with the lack of control that we have over what tools actually
build our library in distro's etc, I fear this might simply be a problem
we defer to the distributions. It's not something that can be handled
stand-alone at the library level. I don't particularly want to wave the
'someone else's problem' - but there are simply external factors that
are outside of our control for this issue - so we can't hope to solve
them all.

I don't mind disabling it.


-- 
Regards
--
Kieran