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

[Rob Herring]

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])

Rob