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 16:38 +0100, Julien Grall wrote:
> On 05/30/2013 04:15 PM, Ian Campbell wrote:
> 
> > 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?
> 
> 
> Yes. GCC will notify that VFP support is not enabled, 

Great!

> except if we use directly mrc and mcr.

Lets not do that!

Ian.



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