[Xen-devel] Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Jeremy Fitzhardinge wrote:
> Linus Torvalds wrote:
>   
> > On Fri, 20 Jun 2008, Ingo Molnar wrote:
> >   
> >     
> > > okay - Jeremy, could you try the fix below? (or tip/master, i just 
> > > pushed this out)
> > >     
> > >       
> > Actually, don't try that one.
> >
> > It needs to be a _byte_ registers, so "ir" was wrong. You need "iq".
> >   
> >     
> Doesn't work, unfortunately:
> {standard input}:20511: Error: Incorrect register `%eax' used with `b' 
> suffix
>         lock; orb %eax,1(%rdi)  # tmp64,
>   
This does work:

               asm volatile(LOCK_PREFIX "orb %1,%0"
                       : CONST_MASK_ADDR(nr, addr)
                       : "iq" ((u8)CONST_MASK(nr))
                       : "memory");

(ie, explicitly casting the mask to u8)

   J

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