linux-kernel - Re: [PATCH v3 1/2] kbuild: move -Werror from KBUILD_CFLAGS to KBUILD

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Date:   Sat, 15 Oct 2022 05:21:25 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v3 1/2] kbuild: move -Werror from KBUILD_CFLAGS to KBUILD_CPPFLAGS

On Sat, Oct 15, 2022 at 1:03 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Thu, Oct 13, 2022 at 03:01:17AM +0900, Masahiro Yamada wrote:
> > CONFIG_WERROR turns warnings into errors, which  happens only for *.c
> > files because -Werror is added to KBUILD_CFLAGS.
> >
> > Adding it to KBUILD_CPPFLAGS makes more sense because preprocessors
> > understand the -Werror option.
> >
> > For example, you can put a #warning directive in any preprocessed code.
> >
> >     warning: #warning "this is a warning message" [-Wcpp]
> >
> > If -Werror is added, it is promoted to an error.
> >
> >     error: #warning "this is a warning message" [-Werror=cpp]
> >
> > This commit moves -Werror to KBUILD_CPPFLAGS so it works in the same way
> > for *.c, *.S, *.lds.S or whatever needs preprocessing.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > ---
> >
> > (no changes since v1)
> >
> >  Makefile | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 85a63a1d29b3..790760d26ea0 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -859,7 +859,8 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >
> >  KBUILD_CFLAGS += $(stackp-flags-y)
> >
> > -KBUILD_CFLAGS-$(CONFIG_WERROR) += -Werror
> > +KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
> > +KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
> >  KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
> >
> >  KBUILD_RUSTFLAGS-$(CONFIG_WERROR) += -Dwarnings
> > --
> > 2.34.1
> >
> >
>
> For what it's worth, this is going to break 32-bit ARM builds with clang
> plus the integrated assembler due to
> https://github.com/ClangBuiltLinux/linux/issues/1315:
>
> clang-16: error: argument unused during compilation: '-march=armv7-a' [-Werror,-Wunused-command-line-argument]
>
> Ultimately, I want -Wunused-command-line-argument to be an error anyways
> (https://github.com/ClangBuiltLinux/linux/issues/1587) but it would be
> nice to get these cleaned up before this goes in.
>
> Cheers,
> Nathan


OK, I will postpone this patch.
Thanks.



-- 
Best Regards
Masahiro Yamada