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

[Rob Clark]

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..

BR,
-R

> Rob