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

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Date:   Tue, 8 Feb 2022 13:23:32 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev, stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] Makefile.extrawarn: Move -Wunaligned-access to W=1

On Thu, Feb 3, 2022 at 8:12 AM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> 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>
>
> > ---


I assume this should be considered as a bug fix
to avoid the error for the combination of CONFIG_WERROR=y
and the latest Clang.

Applied to linux-kbuild/fixes.
Thanks.



> >
> > 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



-- 
Best Regards
Masahiro Yamada