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

[Ilia Mirkin]

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.

  -ilia