Re: [Xen-devel] [PATCH 2/2] xen/arm: don't enable VFP on XEN during the boot

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-05-30 at 15:38 +0100, Julien Grall wrote:
> We can safely remove VFP support in XEN because:
>     - the guest will enable VFP support when a process requires it
>     - XEN doesn't use VFP
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/Rules.mk     |    2 +-
>  xen/arch/arm/setup.c      |    2 --
>  xen/arch/arm/smpboot.c    |    1 -
>  xen/include/asm-arm/vfp.h |   28 ----------------------------
>  4 files changed, 1 insertion(+), 32 deletions(-)
> 
> diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
> index 422ed04..a18e7fd 100644
> --- a/xen/arch/arm/Rules.mk
> +++ b/xen/arch/arm/Rules.mk
> @@ -22,7 +22,7 @@ arm := y
>  ifeq ($(TARGET_SUBARCH),arm32)
>  # Prevent floating-point variables from creeping into Xen.
>  CFLAGS += -msoft-float
> -CFLAGS += -mcpu=cortex-a15 -mfpu=vfpv3 -mfloat-abi=softfp
> +CFLAGS += -mcpu=cortex-a15

Does removing this have the side effect that if we accidentally add a
floating point operation to the hypervisor (very easy to do) it will now
compile with h/w fp, unlike previously where it would generate a call to
a non-existent library call and fail the build?

Since using vfp inside the hypervisor would require more supporting code
failing to build is quite useful.



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