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Subject: Re: [PATCH] drm/i915: Clean up disabled warnings
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
        llvm@lists.linux.dev
References: <20210824232237.2085342-1-nathan@kernel.org>
 <CAKwvOdk2mLem4w05o5cdr0Mz62M2CWeW+5LFnKE5L+pMPqa7WA@mail.gmail.com>
From:   Nathan Chancellor <nathan@kernel.org>
Message-ID: <b8ff7ced-3e5e-603f-6e59-915c97a8f88d@kernel.org>
Date:   Wed, 25 Aug 2021 16:07:48 -0700
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On 8/25/2021 4:03 PM, Nick Desaulniers wrote:
> On Tue, Aug 24, 2021 at 4:23 PM Nathan Chancellor <nathan@kernel.org> wrote:
>>
>> i915 enables a wider set of warnings with '-Wall -Wextra' then disables
>> several with cc-disable-warning. If an unknown flag gets added to
>> KBUILD_CFLAGS when building with clang, all subsequent calls to
>> cc-{disable-warning,option} will fail, meaning that all of these
>> warnings do not get disabled [1].
>>
>> A separate series will address the root cause of the issue by not adding
>> these flags when building with clang [2]; however, the symptom of these
>> extra warnings appearing can be addressed separately by just removing
>> the calls to cc-disable-warning, which makes the build ever so slightly
>> faster because the compiler does not need to be called as much before
>> building.
>>
>> The following warnings are supported by GCC 4.9 and clang 10.0.1, which
>> are the minimum supported versions of these compilers so the call to
>> cc-disable-warning is not necessary. Masahiro cleaned this up for the
>> reset of the kernel in commit 4c8dd95a723d ("kbuild: add some extra
>> warning flags unconditionally").
>>
>> * -Wmissing-field-initializers
>> * -Wsign-compare
>> * -Wtype-limits
>> * -Wunused-parameter
>>
>> -Wunused-but-set-variable was implemented in clang 13.0.0 and
>> -Wframe-address was implemented in clang 12.0.0 so the
>> cc-disable-warning calls are kept for these two warnings.
>>
>> Lastly, -Winitializer-overrides is clang's version of -Woverride-init,
>> which is disabled for the specific files that are problematic. clang
>> added a compatibility alias in clang 8.0.0 so -Winitializer-overrides
>> can be removed.
>>
>> [1]: https://lore.kernel.org/r/202108210311.CBtcgoUL-lkp@intel.com/
>> [2]: https://lore.kernel.org/r/20210824022640.2170859-1-nathan@kernel.org/
>>
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> 
> Thanks for the patch! Do you need to re-ping, rebase, or resend that
> other series?
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

I assume you mean the series below rather than above? I sent this patch 
right after that series and it has one set of reviews so I am hoping the 
i915 maintainers will pick them up soon so this one can be applied 
afterwards or resent.

Thank you for the review!

Cheers,
Nathan

>> ---
>>
>> NOTE: This is based on my series to enable -Wsometimes-initialized here:
>>
>> https://lore.kernel.org/r/20210824225427.2065517-1-nathan@kernel.org/
>>
>> I sent it separately as this can go into whatever release but I would
>> like for that series to go into 5.15.
>>
>>   drivers/gpu/drm/i915/Makefile | 10 ++++------
>>   1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
>> index 335ba9f43d8f..6b38547543b1 100644
>> --- a/drivers/gpu/drm/i915/Makefile
>> +++ b/drivers/gpu/drm/i915/Makefile
>> @@ -13,13 +13,11 @@
>>   # will most likely get a sudden build breakage... Hopefully we will fix
>>   # new warnings before CI updates!
>>   subdir-ccflags-y := -Wall -Wextra
>> -subdir-ccflags-y += $(call cc-disable-warning, unused-parameter)
>> -subdir-ccflags-y += $(call cc-disable-warning, type-limits)
>> -subdir-ccflags-y += $(call cc-disable-warning, missing-field-initializers)
>> +subdir-ccflags-y += -Wno-unused-parameter
>> +subdir-ccflags-y += -Wno-type-limits
>> +subdir-ccflags-y += -Wno-missing-field-initializers
>> +subdir-ccflags-y += -Wno-sign-compare
>>   subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable)
>> -# clang warnings
>> -subdir-ccflags-y += $(call cc-disable-warning, sign-compare)
>> -subdir-ccflags-y += $(call cc-disable-warning, initializer-overrides)
>>   subdir-ccflags-y += $(call cc-disable-warning, frame-address)
>>   subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror
>>
>>
>> base-commit: fb43ebc83e069625cfeeb2490efc3ffa0013bfa4
>> prerequisite-patch-id: 31c28450ed7e8785dce967a16db6d52eff3d7d6d
>> prerequisite-patch-id: 372dfa0e07249f207acc1942ab0e39b13ff229b2
>> prerequisite-patch-id: 1a585fa6cda50c32ad1e3ac8235d3cff1b599978
>> --
>> 2.33.0
>>
> 
>