linux-kernel - Re: [PATCH v2] Makefile.extrawarn: Move -Wunaligned-access to W=1

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Date:   Wed, 2 Feb 2022 15:12:35 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] Makefile.extrawarn: Move -Wunaligned-access to W=1

On Wed, Feb 2, 2022 at 3:07 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> -Wunaligned-access is a new warning in clang that is default enabled for
> arm and arm64 under certain circumstances within the clang frontend (see
> LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows
> 1284 total/70 unique instances of this warning (most of the instances
> are in header files), which is quite noisy.
>
> To keep a normal build green through CONFIG_WERROR, only show this
> warning with W=1, which will allow automated build systems to catch new
> instances of the warning so that the total number can be driven down to
> zero eventually since catching unaligned accesses at compile time would
> be generally useful.
>
> Cc: stable@...r.kernel.org
> Link: https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a
> Link: https://github.com/ClangBuiltLinux/linux/issues/1569
> Link: https://github.com/ClangBuiltLinux/linux/issues/1576
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks to you and Arnd for working out whether this is important to
pursue. Sounds like it is.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
> v1 -> v2: https://lore.kernel.org/r/20220201232229.2992968-1-nathan@kernel.org/
>
> * Move to W=1 instead of W=2 so that new instances are caught (Arnd).
> * Add links to the ClangBuiltLinux issue tracker.
>
>  scripts/Makefile.extrawarn | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index d53825503874..8be892887d71 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-format-zero-length
>  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)
>  endif
>
>  endif
>
> base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c
> --
> 2.35.1
>


-- 
Thanks,
~Nick Desaulniers