[Mesa-dev] [PATCH] c11/threads: resolve link issues with -O0

[Rob Clark]

On Tue, May 24, 2016 at 10:03 AM, Rob Clark <robdclark at gmail.com> wrote:
> On Tue, May 24, 2016 at 9:47 AM, Rob Herring <robh at kernel.org> wrote:
>> On Tue, May 24, 2016 at 8:40 AM, Rob Clark <robdclark at gmail.com> wrote:
>>> On Tue, May 24, 2016 at 9:17 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>> On Tue, May 24, 2016 at 9:15 AM, Rob Herring <robh at kernel.org> wrote:
>>>>> On Tue, May 24, 2016 at 8:09 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>>>> On Tue, May 24, 2016 at 9:06 AM, Rob Herring <robh at kernel.org> wrote:
>>>>>>> On Tue, May 24, 2016 at 4:57 AM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>>>>>>>> From: Emil Velikov <emil.velikov at collabora.com>
>>>>>>>>
>>>>>>>> Add weak symbol notation for the pthread_mutexattr* symbols, thus making
>>>>>>>> the linker happy. When building with -O1 or greater the optimiser will
>>>>>>>> kick in and remove the said functions as they are dead/unreachable code.
>>>>>>>>
>>>>>>>> Ideally we'll enable the optimisations locally, yet that does not seem
>>>>>>>> to work atm.
>>>>>>>>
>>>>>>>> Cc: Alejandro Piñeiro <apinheiro at igalia.com>
>>>>>>>> Cc: Ben Widawsky <ben at bwidawsk.net>
>>>>>>>> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
>>>>>>>> Cc: Mark Janes <mark.a.janes at intel.com>
>>>>>>>> Cc: Rob Clark <robdclark at gmail.com>
>>>>>>>> Cc: Rob Herring <robh at kernel.org>
>>>>>>>> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
>>>>>>>> ---
>>>>>>>> Building with -Wall -Wextra -pedantic and it does not cause any
>>>>>>>> additional warnings/errors.
>>>>>>>> ---
>>>>>>>>  include/c11/threads_posix.h | 26 ++++++++++++++++++++++++++
>>>>>>>>  1 file changed, 26 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/include/c11/threads_posix.h b/include/c11/threads_posix.h
>>>>>>>> index 11d36e4..61b7fab 100644
>>>>>>>> --- a/include/c11/threads_posix.h
>>>>>>>> +++ b/include/c11/threads_posix.h
>>>>>>>> @@ -169,6 +169,32 @@ mtx_destroy(mtx_t *mtx)
>>>>>>>>      pthread_mutex_destroy(mtx);
>>>>>>>>  }
>>>>>>>>
>>>>>>>> +/*
>>>>>>>> + * XXX: Workaround when building with -O0 and without pthreads link.
>>>>>>>> + *
>>>>>>>> + * In such cases constant folding and dead code elimination won't be
>>>>>>>> + * available, thus the compiler will always add the pthread_mutexattr*
>>>>>>>> + * functions into the binary. As we try to link, we'll fail as the
>>>>>>>> + * symbols are unresolved.
>>>>>>>> + *
>>>>>>>> + * Ideally we'll enable the optimisations locally, yet that does not
>>>>>>>> + * seem to work.
>>>>>>>> + *
>>>>>>>> + * So the alternative workaround is to annotate the symbols as weak.
>>>>>>>> + * Thus the linker will be happy and things don't clash when building
>>>>>>>> + * with -O1 or greater.
>>>>>>>> + */
>>>>>>>> +#ifdef HAVE_FUNC_ATTRIBUTE_WEAK
>>>>>>>
>>>>>>> Doesn't this need to get defined somewhere?
>>>>>>
>>>>>> See m4/ax_gcc_func_attribute.m4.
>>>>>
>>>>> Right, but then don't we need "AX_GCC_FUNC_ATTRIBUTE([weak])" added in
>>>>> configure.ac? Only the following are checked:
>>>>>
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([const])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([flatten])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([format])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([malloc])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([packed])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([pure])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([returns_nonnull])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([unused])
>>>>> configure.ac:AX_GCC_FUNC_ATTRIBUTE([warn_unused_result])
>>>>
>>>> Right :) Since Emil says he tested, must be some sort of error in his
>>>> testing procedure. Or he forgot to commit that file.
>>>
>>> hmm, even with the below hunk added, it isn't working for me..  I
>>> suspect Emil might need to double check his generated Makefiles to be
>>> sure they have -O0..
>>
>> Strange. It fails for me so I have -O0, and I can add the weak attribs
>> w/o the ifdef and it works.
>
> and indeed, if I drop the #ifdef guard, it works..
>

ok, not really sure what is going on here.. I do end up w/
-DHAVE_FUNC_ATTRIBUTE_WEAK=1 in generated makefiles, and reverted the
removal of ifdef guard and it is working still.  Possibly it was just
that touching the header (originally deleting the ifdef guard) caused
something to get recompiled which didn't initially..

BR,
-R