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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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, except if we use
directly mrc and mcr.

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