Re: [Xen-devel] [PATCH] x86/gnttab: fix asm() operand in gnttab_clear_flag()

[Lin Ming <mlin@xxxxxxxxxxxxx>]

On Thu, Mar 22, 2012 at 11:55 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> The operand needs to use the 'w' modifier in case the compiler happens
> to pick a register (which apparently it does for no-one but the
> reporter of this problem).
>
> Reported-by: Lin Ming <mlin@xxxxxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/include/asm-x86/grant_table.h
> +++ b/xen/include/asm-x86/grant_table.h
> @@ -54,7 +54,7 @@ static inline void gnttab_clear_flag(uns
>      * Note that this cannot be clear_bit(), as the access must be
>      * confined to the specified 2 bytes.
>      */
> -    asm volatile ("lock btrw %1,%0" : "=m" (*st) : "Ir" (nr), "m" (*st));
> +    asm volatile ("lock btrw %w1,%0" : "=m" (*st) : "Ir" (nr), "m" (*st));

Nice. It works.

Thanks,
Lin Ming

>  }
>
>  /* Foreign mappings of HHVM-guest pages do not modify the type count. */

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