linux-kernel - Re: [PATCH 1/3] [RESEND] ARM: pass -march=armv7-a when building NEON files with clang

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Message-ID: <alpine.LFD.2.20.1602181230440.13632@knanqh.ubzr>
Date:	Thu, 18 Feb 2016 12:31:35 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Jon Medhurst <tixy@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] [RESEND] ARM: pass -march=armv7-a when building NEON
 files with clang

On Thu, 18 Feb 2016, Arnd Bergmann wrote:

> clang ignores the -mfpu=neon flag when building with -march=armv6:
> 
> In file included from lib/raid6/neon1.c:27:
> clang/3.8.0/include/arm_neon.h:28:2: error: "NEON support not enabled"
> 
> There is no real need to build the file with -march=armv6 in a
> multi-CPU enabled kernel, as nothing in here will ever get called
> on an ARMv6 CPU. Adding -march=armv7 doesn't hurt and can only
> improve the code quality.

Is this enough to override a previous -mfpu for gcc?


> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/arm/lib/Makefile | 2 +-
>  lib/raid6/Makefile    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
> index d8a780799506..a86c6c8e0648 100644
> --- a/arch/arm/lib/Makefile
> +++ b/arch/arm/lib/Makefile
> @@ -35,7 +35,7 @@ $(obj)/csumpartialcopy.o:	$(obj)/csumpartialcopygeneric.S
>  $(obj)/csumpartialcopyuser.o:	$(obj)/csumpartialcopygeneric.S
>  
>  ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
> -  NEON_FLAGS			:= -mfloat-abi=softfp -mfpu=neon
> +  NEON_FLAGS			:= -mfloat-abi=softfp -mfpu=neon -march=armv7-a
>    CFLAGS_xor-neon.o		+= $(NEON_FLAGS)
>    obj-$(CONFIG_XOR_BLOCKS)	+= xor-neon.o
>  endif
> diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
> index 3b10a48fa040..4ef3e800fb39 100644
> --- a/lib/raid6/Makefile
> +++ b/lib/raid6/Makefile
> @@ -23,7 +23,7 @@ endif
>  ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
>  NEON_FLAGS := -ffreestanding
>  ifeq ($(ARCH),arm)
> -NEON_FLAGS += -mfloat-abi=softfp -mfpu=neon
> +NEON_FLAGS += -mfloat-abi=softfp -mfpu=neon -march=armv7-a
>  endif
>  ifeq ($(ARCH),arm64)
>  CFLAGS_REMOVE_neon1.o += -mgeneral-regs-only
> -- 
> 2.7.0
> 
>