Re: [Xen-devel] [BUG] x86-64 floating point environment handling

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 28 Nov 2005, at 16:40, Jan Beulich wrote:

> > It's very unlikely we'd implement expensive and complicated logic in
> > Xen to ensure consistency of FP state that noone uses.
> In any case you should use a 64-bit operand size.
If noone uses those fields then it doesn't matter either way. It seems 
that binutils provides no convenient way to force REX.W on that 
instruction.
> Further, I don't share your opinion: For one part, no-one says it's
> only Linux that's going to run on top of Xen, and you really can't make
> claims on what apps namely in a non-paravirtualized environment may or
> may not use. For the other part, things that today don't get used don't
> have to stay that way forever. Why shouldn't software not yet available
> for (or not yet widely used on) Linux use functionality that native
> hardware provides and that Xen (and Linux without the just submitted
> patch) only partly supports?
Well, we'll support those fields properly if there's a sane 
not-too-expensive scheme for saving them properly. I didn't understand 
the scheme that you proposed in your first email.
 -- Keir


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