linux-kernel - Re: [PATCH 05/11] ARM: vfp: use -mfloat-abi=soft to build vfp

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Message-ID: <20111003140411.GB2117@arm.com>
Date:	Mon, 3 Oct 2011 15:04:12 +0100
From:	Dave Martin <dave.martin@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 05/11] ARM: vfp: use -mfloat-abi=soft to build vfp

On Sat, Oct 01, 2011 at 09:21:54PM +0200, Arnd Bergmann wrote:
> Distros are starting to ship with toolchains defaulting to
> hardfloat. Using such a compiler to build the kernel fails
> in the VFP directory with
> 
> arch/arm/vfp/entry.S:1:0: sorry, unimplemented: -mfloat-abi=hard and VFP
> 
> Adding -mfloat-abi=soft to the gcc command line fixes this.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/arm/vfp/Makefile |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/vfp/Makefile b/arch/arm/vfp/Makefile
> index 6de73aa..a81404c 100644
> --- a/arch/arm/vfp/Makefile
> +++ b/arch/arm/vfp/Makefile
> @@ -7,7 +7,7 @@
>  # ccflags-y := -DDEBUG
>  # asflags-y := -DDEBUG
>  
> -KBUILD_AFLAGS	:=$(KBUILD_AFLAGS:-msoft-float=-Wa,-mfpu=softvfp+vfp)
> +KBUILD_AFLAGS	:=$(KBUILD_AFLAGS:-msoft-float=-Wa,-mfpu=softvfp+vfp -mfloat-abi=soft)

Although -mfpu=softvfp+vfp and -mfloat-abi=soft look mutually
contradictory, this seems to have the correct effect, i.e. the
assembler allows floating-point instructions but marks the resulting
object as using the soft-float calling conventions.

The binutils documentation also seems to confirm that that's what
should happen.

I don't see another combination of options for getting this effect.


So, if you like:

Reviewed-by: Dave Martin <dave.martin@...aro.org>

Cheers
---Dave
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