linux-kernel - Re: [PATCH 2/2] Makefile.extrawarn: limit -Wnested-externs to clang

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Message-ID: <20201027014846.GA368335@ubuntu-m3-large-x86>
Date:   Mon, 26 Oct 2020 18:48:46 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH 2/2] Makefile.extrawarn: limit -Wnested-externs to clang

On Mon, Oct 26, 2020 at 11:03:14PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The -Wnested-externs warning has become useless with gcc, since
> this warns every time that BUILD_BUG_ON() or similar macros
> are used.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Also see:

2486baae2cf6 ("objtool: Allow nested externs to enable BUILD_BUG()")
6cf4ecf5c51d ("perf build: Allow nested externs to enable BUILD_BUG() usage")

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  scripts/Makefile.extrawarn | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 6baee1200615..9406f752e355 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -61,7 +61,10 @@ endif
>  ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
>  
>  KBUILD_CFLAGS += -Wdisabled-optimization
> +ifdef CONFIG_CC_IS_CLANG
>  KBUILD_CFLAGS += -Wnested-externs
> +endif
> +
>  KBUILD_CFLAGS += -Wshadow
>  KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
>  KBUILD_CFLAGS += -Wmissing-field-initializers
> -- 
> 2.27.0
>