[Mesa-dev] [PATCH 1/7] util: add MAYBE_UNUSED for config dependent variables

Francisco Jerez currojerez at riseup.net
Mon Apr 18 17:53:28 UTC 2016

Emil Velikov <emil.l.velikov at gmail.com> writes:

> On 18 April 2016 at 04:43, Francisco Jerez <currojerez at riseup.net> wrote:
>> Grazvydas Ignotas <notasas at gmail.com> writes:
>>> On Sun, Apr 17, 2016 at 2:50 AM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>>>> On 16 April 2016 at 02:00, Grazvydas Ignotas <notasas at gmail.com> wrote:
>>>>> This is mostly for variables that are only used in asserts and cause
>>>>> unused-but-set-variable warnings in release builds. Could just use
>>>>> UNUSED directly, but MAYBE_UNUSED should be less confusing and is
>>>>> similar to what the Linux kernel has.
>>>>> And yes __attribute__((unused)) can be used on variables on both GCC 4.2
>>>>> (oldest supported by mesa) and clang 3.0 (just some random old version,
>>>>> nut sure what's the minimum for mesa).
>>>>> Signed-off-by: Grazvydas Ignotas <notasas at gmail.com>
>>>>> ---
>>>>> I have no commit access, if this patch is ok, please someone push.
>>>>>  src/util/macros.h | 2 ++
>>>>>  1 file changed, 2 insertions(+)
>>>>> diff --git a/src/util/macros.h b/src/util/macros.h
>>>>> index 0c8958f..f081bb8 100644
>>>>> --- a/src/util/macros.h
>>>>> +++ b/src/util/macros.h
>>>>> @@ -204,6 +204,8 @@ do {                       \
>>>>>  #define UNUSED
>>>>>  #endif
>>>>> +#define MAYBE_UNUSED UNUSED
>>>>> +
>>>> Hell yeah !
>>>> A thing that comes to mind ... a while back we've been wondering about
>>>> (re)naming these just the the way we do in the kernel. Namely
>>>> __maybe_unused in this case. Can you give that one a try and link a
>>>> branch.
>>> I hope you mean something like this?
>>> https://github.com/notaz/mesa/commits/warnings
>> You guys know that in standard C any identifier (including a
>> preprocessor define) starting with double underscore is reserved for the
>> implementation and causes the program's behavior to be undefined?  The
>> kernel is kind of part of the implementation so they can do whatever
>> they want, but it seems dubious to do the same in a userspace library.
>> How about you use a single (or no) underscore if people prefer the
>> lowercase spelling?
> I do recall this. As mentioned before (to Jose I believe) sadly the
> cat is out of the bag. Both within mesa itself and also in other
> projects.
> IIRC the conclusion from last time was along the lines of "[I guess]
> it's ok if it does not break things". So far scons (linux + windows)
> look fine - autoconf's normal make looks ok as well (make check takes
> a while) ;-)
> Personally I'd opt for consistency across projects. It gives us extra
> reassurance that things are unlikely to break under our feet.
> Although yes, it does suck (a bit) that thing have turned out that way.
So you're suggesting that the precedent set by some other projects [that
happen to be mainly the kernel which has a wildly different set of
requirements than userspace code] should have more weight than
consistency with *Mesa's* own macro capitalization rules and the C

Sorry, but it seems rather pointless to me to ask GraÅžvydas to break the
rules knowingly.  His original patch has my vote and:

Reviewed-by: Francisco Jerez <currojerez at riseup.net>

> -Emil
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