linux-kernel - Re: [PATCH v2] kbuild: Move -Wenum-enum-conversion to W=2

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Message-ID: <20241202161610.GA2845796@thelio-3990X>
Date: Mon, 2 Dec 2024 09:16:10 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nicolas Schier <nicolas@...sle.eu>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Arnd Bergmann <arnd@...db.de>, Aleksei Vetrov <vvvvvv@...gle.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, patches@...ts.linux.dev,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] kbuild: Move -Wenum-enum-conversion to W=2

Masahiro, could you please pick this up? The lore link is below in case
it is no longer in your inbox (or I can resend).

https://lore.kernel.org/20241017-disable-two-clang-enum-warnings-v2-1-163ac04346ae@kernel.org/

On Thu, Oct 17, 2024 at 10:09:22AM -0700, Nathan Chancellor wrote:
> -Wenum-enum-conversion was strengthened in clang-19 to warn for C, which
> caused the kernel to move it to W=1 in commit 75b5ab134bb5 ("kbuild:
> Move -Wenum-{compare-conditional,enum-conversion} into W=1") because
> there were numerous instances that would break builds with -Werror.
> Unfortunately, this is not a full solution, as more and more developers,
> subsystems, and distributors are building with W=1 as well, so they
> continue to see the numerous instances of this warning.
> 
> Since the move to W=1, there have not been many new instances that have
> appeared through various build reports and the ones that have appeared
> seem to be following similar existing patterns, suggesting that most
> instances of this warning will not be real issues. The only alternatives
> for silencing this warning are adding casts (which is generally seen as
> an ugly practice) or refactoring the enums to macro defines or a unified
> enum (which may be undesirable because of type safety in other parts of
> the code).
> 
> Move the warning to W=2, where warnings that occur frequently but may be
> relevant should reside.
> 
> Cc: stable@...r.kernel.org
> Fixes: 75b5ab134bb5 ("kbuild: Move -Wenum-{compare-conditional,enum-conversion} into W=1")
> Link: https://lore.kernel.org/ZwRA9SOcOjjLJcpi@google.com/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> Changes in v2:
> - Move -Wenum-enum-conversion to W=2, instead of disabling it
>   outright (Arnd)
> - Leave -Wenum-compare-conditional in W=1, as there are not that
>   many instances, so it can be turned on fully at some point (Arnd)
> - Link to v1: https://lore.kernel.org/r/20241016-disable-two-clang-enum-warnings-v1-1-ae886d7a0269@kernel.org
> ---
>  scripts/Makefile.extrawarn | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 1d13cecc7cc7808610e635ddc03476cf92b3a8c1..04faf15ed316a9c291dc952b6cc40fb6c8c330cf 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -130,7 +130,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
>  KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
>  KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
>  KBUILD_CFLAGS += -Wno-enum-compare-conditional
> -KBUILD_CFLAGS += -Wno-enum-enum-conversion
>  endif
>  
>  endif
> @@ -154,6 +153,10 @@ KBUILD_CFLAGS += -Wno-missing-field-initializers
>  KBUILD_CFLAGS += -Wno-type-limits
>  KBUILD_CFLAGS += -Wno-shift-negative-value
>  
> +ifdef CONFIG_CC_IS_CLANG
> +KBUILD_CFLAGS += -Wno-enum-enum-conversion
> +endif
> +
>  ifdef CONFIG_CC_IS_GCC
>  KBUILD_CFLAGS += -Wno-maybe-uninitialized
>  endif
> 
> ---
> base-commit: 8e929cb546ee42c9a61d24fae60605e9e3192354
> change-id: 20241016-disable-two-clang-enum-warnings-e7994d44f948
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@...nel.org>
>