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

From: Roland McGrath
Date: Wed May 21 2008 - 20:54:56 EST

> 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.

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