linux-kernel - Re: [PATCH] Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough for clang

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Date:   Sat, 10 Aug 2019 12:32:03 -0700
From:   Joe Perches <joe@...ches.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] Makefile: Convert -Wimplicit-fallthrough=3 to just
 -Wimplicit-fallthrough for clang

On Mon, 2019-08-05 at 15:11 -0700, Joe Perches wrote:
> A compilation -Wimplicit-fallthrough warning was enabled by
> commit a035d552a93b ("Makefile: Globally enable fall-through warning")
> 
> Even though clang 10.0.0 does not currently support this warning
> without a patch, clang currently does not support a value for this
> option.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=39382
> 
> The gcc default for this warning is 3 so removing the =3 has no
> effect for gcc and enables the warning for patched versions of clang.
> 
> Also remove the =3 from an existing use in a parisc Makefile:
> arch/parisc/math-emu/Makefile

Hey Linus,

What does it take for this sort of patch to be applied by you?

> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
>  Makefile                      | 2 +-
>  arch/parisc/math-emu/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 5ee6f6889869..a3985421fd29 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -845,7 +845,7 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
>  KBUILD_CFLAGS += -Wdeclaration-after-statement
>  
>  # Warn about unmarked fall-throughs in switch statement.
> -KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=3,)
> +KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
>  
>  # Variable Length Arrays (VLAs) should not be used anywhere in the kernel
>  KBUILD_CFLAGS += -Wvla
> diff --git a/arch/parisc/math-emu/Makefile b/arch/parisc/math-emu/Makefile
> index 55c1396580a4..3747a0cbd3b8 100644
> --- a/arch/parisc/math-emu/Makefile
> +++ b/arch/parisc/math-emu/Makefile
> @@ -18,4 +18,4 @@ obj-y	 := frnd.o driver.o decode_exc.o fpudispatch.o denormal.o \
>  # other very old or stripped-down PA-RISC CPUs -- not currently supported
>  
>  obj-$(CONFIG_MATH_EMULATION)	+= unimplemented-math-emulation.o
> -CFLAGS_REMOVE_fpudispatch.o	= -Wimplicit-fallthrough=3
> +CFLAGS_REMOVE_fpudispatch.o	= -Wimplicit-fallthrough
>