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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 25 Aug 2021 16:03:39 -0700
Message-ID: <CAKwvOdk2mLem4w05o5cdr0Mz62M2CWeW+5LFnKE5L+pMPqa7WA@mail.gmail.com>
Subject: Re: [PATCH] drm/i915: Clean up disabled warnings
To:     Nathan Chancellor <nathan@kernel.org>
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
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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>

> ---
>
> 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
>


-- 
Thanks,
~Nick Desaulniers