linux-kernel - Re: [PATCH 2/2] kbuild: add -Wundef to KBUILD

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Date:   Fri, 9 Dec 2022 10:49:16 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 2/2] kbuild: add -Wundef to KBUILD_CPPFLAGS for W=1 builds

On Tue, Dec 06, 2022 at 01:07:31PM +0900, Masahiro Yamada wrote:
> The use of an undefined macro in an #if directive is warned, but only
> in *.c files. No warning from other files such as *.S, *.lds.S.
> 
> Since -Wundef is a preprocessor-related warning, it should be added to
> KBUILD_CPPFLAGS instead of KBUILD_CFLAGS.
> 
> My previous attempt [1] uncovered several warnings, and could not finish
> fixing them all.
> 
> This commit adds -Wundef to KBUILD_CPPFLAGS for W=1 builds in order to
> block new breakages. (The kbuild test robot tests with W=1)
> 
> We can fix the warnings one by one. After we fix all of them, we can
> make this default in the top Makefile, and remove -Wundef from
> KBUILD_CFLAGS.
> 
> [1]: https://lore.kernel.org/all/20221012180118.331005-2-masahiroy@kernel.org/
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

Looks like the robot already found a few so this clearly works as
intended.

> ---
> 
>  scripts/Makefile.extrawarn | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 6bbba36c5969..40cd13eca82e 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -38,6 +38,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-type-limits
>  KBUILD_CFLAGS += -Wno-shift-negative-value
>  
> +KBUILD_CPPFLAGS += -Wundef
>  KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
>  
>  else
> -- 
> 2.34.1
> 
>