linux-kernel - Re: [PATCH] drm/i915: Disable -Wuninitialized for intel

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Message-ID: <20181217174155.GA857@flashbox>
Date:   Mon, 17 Dec 2018 10:41:55 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: [PATCH] drm/i915: Disable -Wuninitialized for intel_breadcrumbs.o

On Thu, Oct 25, 2018 at 12:36:01PM -0700, Nathan Chancellor wrote:
> This warning is disabled by default in scripts/Makefile.extrawarn when
> W= is not provided but this Makefile adds -Wall after this warning is
> disabled so it shows up in the build when it shouldn't:
> 
> In file included from drivers/gpu/drm/i915/intel_breadcrumbs.c:895:
> drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c:350:34: error:
> variable 'wq' is uninitialized when used within its own initialization
> [-Werror,-Wuninitialized]
>         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
>                                         ^~
> ./include/linux/wait.h:74:63: note: expanded from macro
> 'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
>         struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
>                                ~~~~                                  ^~~~
> ./include/linux/wait.h:72:33: note: expanded from macro
> '__WAIT_QUEUE_HEAD_INIT_ONSTACK'
>         ({ init_waitqueue_head(&name); name; })
>                                        ^~~~
> 1 error generated.
> 
> This warning looks to be a false positive given that init_waitqueue_head
> initializes name before it is used. Rather than disable the warning for
> the full folder like commit 46e2068081e9 ("drm/i915: Disable some extra
> clang warnings"), just disable it for the one problematic file because
> it could be a useful warning for other cases.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/220
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/gpu/drm/i915/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 1c2857f13ad4..f36c420afb99 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -26,6 +26,7 @@ subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror
>  
>  # Fine grained warnings disable
>  CFLAGS_i915_pci.o = $(call cc-disable-warning, override-init)
> +CFLAGS_intel_breadcrumbs.o = $(call cc-disable-warning, uninitialized)
>  CFLAGS_intel_fbdev.o = $(call cc-disable-warning, override-init)
>  
>  subdir-ccflags-y += \
> -- 
> 2.19.1
> 

Gentle ping for review.

Nathan