linux-kernel - Re: [PATCH] Makefile: Move -Wno-unused-but-set-variable out of GCC only block

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Date:   Fri, 30 Apr 2021 15:49:00 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "# 3.4.x" <stable@...r.kernel.org>, Jian Cai <jiancai@...gle.com>
Subject: Re: [PATCH] Makefile: Move -Wno-unused-but-set-variable out of GCC
 only block

On Wed, Apr 28, 2021 at 6:24 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Currently, -Wunused-but-set-variable is only supported by GCC so it is
> disabled unconditionally in a GCC only block (it is enabled with W=1).
> clang currently has its implementation for this warning in review so
> preemptively move this statement out of the GCC only block and wrap it
> with cc-disable-warning so that both compilers function the same.
>
> Cc: stable@...r.kernel.org
> Link: https://reviews.llvm.org/D100581

Thanks for the patch.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

(That's actually one of Jian's teammates working on implementing that
warning).  Tested with https://reviews.llvm.org/D100581 applied, which
I do fully expect to land in LLVM soon.

> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  Makefile | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index f03888cdba4e..911d839cfea8 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -775,16 +775,16 @@ KBUILD_CFLAGS += -Wno-gnu
>  KBUILD_CFLAGS += -mno-global-merge
>  else
>
> -# These warnings generated too much noise in a regular build.
> -# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
> -KBUILD_CFLAGS += -Wno-unused-but-set-variable
> -
>  # Warn about unmarked fall-throughs in switch statement.
>  # Disabled for clang while comment to attribute conversion happens and
>  # https://github.com/ClangBuiltLinux/linux/issues/636 is discussed.
>  KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
>  endif
>
> +# These warnings generated too much noise in a regular build.
> +# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
> +KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
> +
>  KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
>  ifdef CONFIG_FRAME_POINTER
>  KBUILD_CFLAGS  += -fno-omit-frame-pointer -fno-optimize-sibling-calls
>
> base-commit: d8201efe75e13146ebde433745c7920e15593baf
> --
> 2.31.1.362.g311531c9de
>
> --

-- 
Thanks,
~Nick Desaulniers