linux-kernel - Re: [PATCH 07/15] arm64: use -mno-implicit-float instead of -mgeneral-regs-only

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Date:   Fri, 3 Nov 2017 18:02:57 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>
Subject: Re: [PATCH 07/15] arm64: use -mno-implicit-float instead of
 -mgeneral-regs-only

On Fri, Nov 03, 2017 at 10:11:52AM -0700, Sami Tolvanen wrote:
> From: Greg Hackmann <ghackmann@...gle.com>
> 
> LLVM bug 30792 causes clang's AArch64 backend to crash compiling
> arch/arm64/crypto/aes-ce-cipher.c.  Replacing -mgeneral-regs-only with
> -mno-implicit-float is the suggested workaround.
> 
> Signed-off-by: Greg Hackmann <ghackmann@...gle.com>
> Cc: Matthias Kaehlcke <mka@...omium.org>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Ah, so I guess this is what I was hitting when testing with clang 5.0.0.

I was under the impression that this series was jsut enablnig LTO
support, not clang support generally.

It would be much nicer if we could depend on a fixed clang to start
with...

Thanks,
Mark.

> ---
>  arch/arm64/Makefile | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 939b310913cf..eb6f3c9ec6cb 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -45,7 +45,13 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
>    endif
>  endif
>  
> -KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr) $(brokengasinst)
> +ifeq ($(cc-name),clang)
> +# This is a workaround for https://bugs.llvm.org/show_bug.cgi?id=30792.
> +KBUILD_CFLAGS	+= -mno-implicit-float
> +else
> +KBUILD_CFLAGS	+= -mgeneral-regs-only
> +endif
> +KBUILD_CFLAGS	+= $(lseinstr) $(brokengasinst)
>  KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
>  KBUILD_CFLAGS	+= $(call cc-option, -mpc-relative-literal-loads)
>  KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
> -- 
> 2.15.0.403.gc27cc4dac6-goog
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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