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From: Chris Wilson <chris@chris-wilson.co.uk>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-gfx@lists.freedesktop.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	clang-built-linux@googlegroups.com,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Zero initialize this_cpu in busywait_stop
Date: Fri, 08 Mar 2019 08:27:10 +0000	[thread overview]
Message-ID: <155203363088.27405.11887329278848171622@skylake-alporthouse-com> (raw)
In-Reply-To: <20190308012023.5709-1-natechancellor@gmail.com>

Quoting Nathan Chancellor (2019-03-08 01:20:24)
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/gpu/drm/i915/i915_request.c:1032:6: warning: variable 'this_cpu'
> is used uninitialized whenever '&&' condition is false
> [-Wsometimes-uninitialized]
> 
> time_after expands to use two typecheck with logical ANDs between them.
> typecheck evaluates to 1 but Clang clearly gets confused with the logic
> that as semantic analysis happens early in the pipeline. Fix this by
> just zero initializing this_cpu as it will always be properly
> initialized before the comparison below.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/415
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
> 
> Alternatively, this can be solved by having the return value of
> local_clock_us(&this_cpu) be a local variable but this seems less
> controversial.

I'll just wait for clang to be fixed, as this severely undermines any
respect I have for its semantic analysis.
-Chris

WARNING: multiple messages have this Message-ID (diff)
From: Chris Wilson <chris@chris-wilson.co.uk>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-gfx@lists.freedesktop.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	clang-built-linux@googlegroups.com,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: Re: [PATCH] drm/i915: Zero initialize this_cpu in busywait_stop
Date: Fri, 08 Mar 2019 08:27:10 +0000	[thread overview]
Message-ID: <155203363088.27405.11887329278848171622@skylake-alporthouse-com> (raw)
In-Reply-To: <20190308012023.5709-1-natechancellor@gmail.com>

Quoting Nathan Chancellor (2019-03-08 01:20:24)
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/gpu/drm/i915/i915_request.c:1032:6: warning: variable 'this_cpu'
> is used uninitialized whenever '&&' condition is false
> [-Wsometimes-uninitialized]
> 
> time_after expands to use two typecheck with logical ANDs between them.
> typecheck evaluates to 1 but Clang clearly gets confused with the logic
> that as semantic analysis happens early in the pipeline. Fix this by
> just zero initializing this_cpu as it will always be properly
> initialized before the comparison below.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/415
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
> 
> Alternatively, this can be solved by having the return value of
> local_clock_us(&this_cpu) be a local variable but this seems less
> controversial.

I'll just wait for clang to be fixed, as this severely undermines any
respect I have for its semantic analysis.
-Chris
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

  parent reply	other threads:[~2019-03-08  8:27 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-08  1:20 [PATCH] drm/i915: Zero initialize this_cpu in busywait_stop Nathan Chancellor
2019-03-08  2:02 ` ✓ Fi.CI.BAT: success for " Patchwork
2019-03-08  6:20 ` ✓ Fi.CI.IGT: " Patchwork
2019-03-08  8:27 ` Chris Wilson [this message]
2019-03-08  8:27   ` [PATCH] " Chris Wilson
2019-03-08 19:26   ` [Intel-gfx] " Nick Desaulniers
2019-03-08 20:43 ` ✗ Fi.CI.BAT: failure for drm/i915: Zero initialize this_cpu in busywait_stop (rev2) Patchwork

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