Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

[H. Peter Anvin]

Roland McGrath wrote:
> > The biggest potential problem with this that I see is that relying on 
> > CPUID can mess with certain virtualization solutions.  Another option to 
> > accomplish the same thing would be to have a system call (preferrably a 
> > prctl, since it is at least in theory personality-dependent) to query 
> > what information is included in the fpstate data - since it will always 
> > be the same for any particular kernel.
>
> It's easy and cheap to add an indicator to the vDSO for this.

Yes, but I suspect for legacy apps running without vDSO might matter.

	-hpa
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