[Barrelfish-users] [ARM] About vfp instructions

[Kornilios Kourtis]

Hi,

On Thu, May 30, 2013 at 06:41:13PM +0800, Wang Nan wrote:
> Hi,
> 
> Some compiler generates vfp instructions such as vpush, vldr for normal
> code in cpu driver, which introduces complexity (related to fpu state).
> I propose a patch which disables vfp instructions in cpu driver code:
> 
> 
> diff --git a/hake/ARMv7.hs b/hake/ARMv7.hs
> index 142f524..03ed5c4 100644
> --- a/hake/ARMv7.hs
> +++ b/hake/ARMv7.hs
> @@ -116,6 +116,7 @@ kernelCFlags = [ Str s | s <- [ "-fno-builtin",
>                                  "-march=armv7-a",
>                                  "-mapcs",
>                                  "-mabi=aapcs-linux",
> +                                "-mfloat-abi=soft",
>                                  "-fPIE",
>                                  "-U__linux__",
>                                  "-Wall",
> 

Makes sense -- I've applied to our tree. Thanks!

> On the other hand, vfp and A_SIMD instruction should be allowed in user
> code, and fpu state should be saved and restored during context
> switching. In current omap code, I don't find vfp related code.  Does
> any one can implements them?

Indeed VFP-aware context switching seems to be missing. We will add it on
our TODO list, but from a quick look it does not seem to be trivial. If
somebody is interested in implementing it, we would be happy to help.

cheers,
Kornilios.

-- 
Kornilios Kourtis