[PATCH 4.9 to 5.4] Makefile.extrawarn: Move -Wunaligned-access to W=1

[PATCH 4.9 to 5.4] Makefile.extrawarn: Move -Wunaligned-access to W=1

[Nathan Chancellor]

commit 1cf5f151d25fcca94689efd91afa0253621fb33a upstream.

-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>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[nathan: Fix conflict due to lack of afe956c577b2d]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---

I am not sure how many people are using ToT clang with ARCH=arm on
stable but given how noisy this warning can be, I think it is worth
applying this to all applicable stable branches.

This applies to 4.9 through 5.4 with 'patch -Np1'.

 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index ca08f2fe7c34..854e2ba9daa2 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -49,6 +49,7 @@ KBUILD_CFLAGS += -Wno-format
 KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif

base-commit: 52871671099d1bb3fca5ed076029e4b937bfc053
-- 
2.35.1

Re: [PATCH 4.9 to 5.4] Makefile.extrawarn: Move -Wunaligned-access to W=1

[Greg Kroah-Hartman]

On Mon, Feb 14, 2022 at 09:16:42AM -0700, Nathan Chancellor wrote:
> commit 1cf5f151d25fcca94689efd91afa0253621fb33a upstream.
> 
> -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>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> [nathan: Fix conflict due to lack of afe956c577b2d]
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> 
> I am not sure how many people are using ToT clang with ARCH=arm on
> stable but given how noisy this warning can be, I think it is worth
> applying this to all applicable stable branches.
> 
> This applies to 4.9 through 5.4 with 'patch -Np1'.
> 
>  scripts/Makefile.extrawarn | 1 +
>  1 file changed, 1 insertion(+)

Now queued up, thanks.

greg k-h