From: Joe Perches <joe@perches.com>
To: Nathan Huckleberry <nhuck@google.com>,
yamada.masahiro@socionext.com, michal.lkml@markovi.net,
Nathan Chancellor <natechancellor@gmail.com>
Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH v2] kbuild: Change fallthrough comments to attributes
Date: Mon, 12 Aug 2019 15:40:45 -0700 [thread overview]
Message-ID: <814c1b19141022946d3e0f7e24d69658d7a512e4.camel@perches.com> (raw)
In-Reply-To: <20190812221416.139678-1-nhuck@google.com>
On Mon, 2019-08-12 at 15:14 -0700, Nathan Huckleberry wrote:
> Clang does not support the use of comments to label
> intentional fallthrough. This patch replaces some uses
> of comments to attributesto cut down a significant number
> of warnings on clang (from ~50000 to ~200). Only comments
> in commonly used header files have been replaced.
>
> Since there is still quite a bit of noise, this
> patch moves -Wimplicit-fallthrough to
> Makefile.extrawarn if you are compiling with
> clang.
Unmodified clang does not emit this warning without a patch.
> diff --git 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
It'd be better to remove CONFIG_CC_IS_CLANG everywhere
eventually as it adds complexity and makes .config files
not portable to multiple systems.
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
[]
> @@ -253,4 +253,8 @@
> */
> #define __weak __attribute__((__weak__))
>
> +#if __has_attribute(fallthrough)
> +#define __fallthrough __attribute__((fallthrough))
This should be __attribute__((__fallthrough__))
And there is still no agreement about whether this should
be #define fallthrough or #define __fallthrough
https://lore.kernel.org/patchwork/patch/1108577/
> diff --git a/include/linux/jhash.h b/include/linux/jhash.h
[]
> @@ -86,19 +86,43 @@ static inline u32 jhash(const void *key, u32 length, u32 initval)
[]
> + case 12:
> + c += (u32)k[11]<<24;
> + __fallthrough;
You might consider trying out the scripted conversion tool
attached to this email:
https://lore.kernel.org/lkml/61ddbb86d5e68a15e24ccb06d9b399bbf5ce2da7.camel@perches.com/
next prev parent reply other threads:[~2019-08-12 22:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 21:47 [PATCH] kbuild: Change fallthrough comments to attributes Nathan Huckleberry
2019-08-12 22:14 ` [PATCH v2] " Nathan Huckleberry
2019-08-12 22:40 ` Joe Perches [this message]
2019-08-12 23:11 ` Nick Desaulniers
2019-08-12 23:23 ` Joe Perches
2019-08-13 6:33 ` Nathan Chancellor
2019-08-13 7:04 ` Joe Perches
2019-08-13 7:43 ` Joe Perches
2019-08-13 9:48 ` David Laight
2019-08-12 23:06 ` [PATCH] " Nick Desaulniers
2019-08-13 7:15 ` Christoph Hellwig
2019-08-15 21:07 ` kbuild test robot
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