[Mesa-dev] [PATCH v2] c11/threads: resolve link issues with -O0

[Rob Clark]

On Tue, May 24, 2016 at 11:23 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.
>
> v2: Add the AX_GCC_FUNC_ATTRIBUTE([weak]) hunk in configure.
>
> 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>

Tested-by: Rob Clark <robdclark at gmail.com>

> ---
>  configure.ac                |  1 +
>  include/c11/threads_posix.h | 26 ++++++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/configure.ac b/configure.ac
> index 47c138a..fc0b1db 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -233,6 +233,7 @@ AX_GCC_FUNC_ATTRIBUTE([pure])
>  AX_GCC_FUNC_ATTRIBUTE([returns_nonnull])
>  AX_GCC_FUNC_ATTRIBUTE([unused])
>  AX_GCC_FUNC_ATTRIBUTE([warn_unused_result])
> +AX_GCC_FUNC_ATTRIBUTE([weak])
>
>  AM_CONDITIONAL([GEN_ASM_OFFSETS], test "x$GEN_ASM_OFFSETS" = xyes)
>
> 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
> +__attribute__((weak))
> +int pthread_mutexattr_init(pthread_mutexattr_t *attr);
> +
> +__attribute__((weak))
> +int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);
> +
> +__attribute__((weak))
> +int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
> +#endif
> +
>  // 7.25.4.2
>  static inline int
>  mtx_init(mtx_t *mtx, int type)
> --
> 2.8.2
>