Re: [Xen-merge] fs/gs handling

[Andi Kleen <ak@xxxxxxx>]

On Wednesday 24 August 2005 01:36, Kurt Garloff wrote:
> Hi Andi,
>
> On Fri, Aug 12, 2005 at 11:26:27AM +0200, Andi Kleen wrote:
> > On Fri, Aug 12, 2005 at 05:11:49AM +0200, Kurt Garloff wrote:
> > > On Thu, Aug 11, 2005 at 07:41:45PM -0700, Chris Wright wrote:
> > > >  #define deactivate_mm(tsk, mm) \
> > > > -       asm("movl %0,%%fs ; movl %0,%%gs": :"r" (0))
> > > > +       asm("mov %0,%%fs ; mov %0,%%gs": :"r" (0))
> > >
> > > mov works for both x86 and x86-64 ...
> > > ... though I don't know whether that's relevant here.
> >
> > It's not. Segment registers cannot be 64bit.
>
> mov will work (the assembler knows the size of a segment register),
> movl won't. movw would be correct. segment selectors are 16bit.

Actually movl works too for segment registers. 
movw is even discouraged because it  generates a unnecessary 16bit prefix.

-Andi

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