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

[Rob Herring]

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.

Rob