[v2] Makefile.extrawarn: Move -Wunaligned-access to W=1

-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@vger.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@kernel.org>
---

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(+)


base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c

On Wed, Feb 2, 2022 at 3:07 PM Nathan Chancellor <nathan@kernel.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@vger.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@kernel.org>

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