From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Nathan Huckleberry <nhuck@google.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Michal Marek <michal.lkml@markovi.net>,
Joe Perches <joe@perches.com>,
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] kbuild: Require W=1 for -Wimplicit-fallthrough with clang
Date: Thu, 15 Aug 2019 15:50:52 -0700 [thread overview]
Message-ID: <CAKwvOdk+NQCKZ4EXAukaKYK4R9CDaNWVY_aDxXaeQrLfo_Z=nw@mail.gmail.com> (raw)
In-Reply-To: <20190815204529.GA69414@archlinux-threadripper>
On Thu, Aug 15, 2019 at 1:45 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Thu, Aug 15, 2019 at 11:20:29AM -0700, 'Nathan Huckleberry' via Clang Built Linux wrote:
> > Clang is updating to support -Wimplicit-fallthrough on C
> > https://reviews.llvm.org/D64838. Since clang does not
> > support the comment version of fallthrough annotations
> > this update causes an additional 50k warnings. Most
> > of these warnings (>49k) are duplicates from header files.
> >
> > This patch is intended to be reverted after the warnings
> > have been cleaned up.
> >
> > Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> > ---
> > Makefile | 4 ++++
> > scripts/Makefile.extrawarn | 3 +++
> > 2 files changed, 7 insertions(+)
> >
> > diff --git a/Makefile b/Makefile
> > index 1b23f95db176..93b9744e66a2 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -846,7 +846,11 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
> > KBUILD_CFLAGS += -Wdeclaration-after-statement
> >
> > # Warn about unmarked fall-throughs in switch statement.
> > +# If the compiler is clang, this warning is only enabled if W=1 in
> > +# Makefile.extrawarn
> > +ifndef CONFIG_CC_IS_CLANG
> > KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
> > +endif
> >
> > # Variable Length Arrays (VLAs) should not be used anywhere in the kernel
> > KBUILD_CFLAGS += -Wvla
> > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> > index a74ce2e3c33e..e12359d69bb7 100644
> > --- a/scripts/Makefile.extrawarn
> > +++ b/scripts/Makefile.extrawarn
> > @@ -30,6 +30,9 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable)
> > warning-1 += $(call cc-option, -Wunused-const-variable)
> > warning-1 += $(call cc-option, -Wpacked-not-aligned)
> > warning-1 += $(call cc-option, -Wstringop-truncation)
> > +ifdef CONFIG_CC_IS_CLANG
> > +KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
>
> Shouldn't this be warning-1?
+1
>
> > +endif
> > # The following turn off the warnings enabled by -Wextra
> > warning-1 += -Wno-missing-field-initializers
> > warning-1 += -Wno-sign-compare
> > --
> > 2.23.0.rc1.153.gdeed80330f-goog
> >
>
> I am still not a huge fan of the CONFIG_CC_IS_CLANG ifdefs but I don't
> really see a much cleaner way to get around this. Some that come to
> mind:
>
> * Leave Makefile alone and add
>
> KBUILD_CFLAGS += -Wno-implicit-fallthrough
>
> in the CONFIG_CC_IS_CLANG section of scripts/Makefile.extrawarn
Yeah, I think this might be cleaner. -Wimplicit-fallthrough
-Wno-implicit-fallthrough will be passed to Clang, but "last one
wins." A smaller patch makes it more likely to be revertable without
potentially having to resolve any conflicts. Would you mind sending a
V2 with that change? You can include Nathan's Suggested-by tag.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2019-08-15 22:51 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-15 18:20 [PATCH] kbuild: Require W=1 for -Wimplicit-fallthrough with clang Nathan Huckleberry
2019-08-15 20:45 ` Nathan Chancellor
2019-08-15 22:50 ` Nick Desaulniers [this message]
2019-08-15 22:58 ` [PATCH v2] " Nathan Huckleberry
2019-08-15 23:04 ` Nick Desaulniers
2019-08-18 16:43 ` Masahiro Yamada
2019-08-18 18:43 ` Nathan Chancellor
2019-08-19 3:05 ` Masahiro Yamada
2019-08-27 0:41 ` [PATCH] kbuild: Do not enable -Wimplicit-fallthrough for clang for now Nathan Chancellor
2019-08-28 16:20 ` Masahiro Yamada
2019-08-28 16:44 ` Miguel Ojeda
2019-08-28 17:39 ` Nick Desaulniers
2019-08-28 17:44 ` Nick Desaulniers
2019-08-29 17:18 ` Masahiro Yamada
2019-08-28 18:02 ` Gustavo A. R. Silva
2019-08-15 22:59 ` [PATCH] kbuild: Require W=1 for -Wimplicit-fallthrough with clang Miguel Ojeda
2019-08-15 23:05 ` Nick Desaulniers
2019-08-15 23:53 ` Miguel Ojeda
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