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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 17 Jun 2019 10:48:51 -0700
Message-ID: <CAKwvOdk4yvWQynR4uPzDFPonfVTTDt7_ZaqR2MJGUm78PQ4Gfg@mail.gmail.com>
Subject: Re: [PATCH] kbuild: Remove unnecessary -Wno-unused-value
To:     Nathan Huckleberry <nhuck@google.com>
Cc:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Mon, Jun 17, 2019 at 10:28 AM Nathan Huckleberry <nhuck@google.com> wrote:
>
> This flag turns off several other warnings that would
> be useful. Most notably -warn_unused_result is disabled.
> All of the following warnings are currently disabled:
>
> UnusedValue
> |-UnusedComparison
>   |-warn_unused_comparison
> |-UnusedResult
>   |-warn_unused_result
> |-UnevaluatedExpression
>   |-PotentiallyEvaluatedExpression
>     |-warn_side_effects_typeid
>   |-warn_side_effects_unevaluated_context
> |-warn_unused_expr
> |-warn_unused_voidptr
> |-warn_unused_container_subscript_expr
> |-warn_unused_call
>
> With this flag removed there are ~10 warnings.
> Patches have been submitted for each of these warnings.
>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Cc: clang-built-linux@googlegroups.com
> Link: https://github.com/ClangBuiltLinux/linux/issues/520
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>

Most importantly, it fixes __must_check, which has been silently not
working w/ Clang.  Nathan sent patches for the issues we could find w/
x86_65 and arm64 allyesconfig builds, and even fixed a bug in Clang.
https://reviews.llvm.org/D63369

Thanks for all of the work that went into this.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  scripts/Makefile.extrawarn | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 3ab8d1a303cd..b293246e48fe 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -68,7 +68,6 @@ else
>
>  ifdef CONFIG_CC_IS_CLANG
>  KBUILD_CFLAGS += -Wno-initializer-overrides
> -KBUILD_CFLAGS += -Wno-unused-value
>  KBUILD_CFLAGS += -Wno-format
>  KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-format-zero-length
> --
> 2.22.0.410.gd8fdbe21b5-goog
>


-- 
Thanks,
~Nick Desaulniers