Re: [Xen-devel] [PATCH] x86: Fix grant-table build error

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.03.12 at 16:21, Lin Ming <mlin@xxxxxxxxxxxxx> wrote:
> Fixes build error with btrw instruction.
> 
> xen-unstable/xen/include/asm/grant_table.h:57: 
> Error: Incorrect register `%edx' used with `w' suffix

With what gcc?

> Signed-off-by: Lin Ming <mlin@xxxxxxxxxxxxx>
> ---
>  xen/include/asm-x86/grant_table.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/xen/include/asm-x86/grant_table.h 
> b/xen/include/asm-x86/grant_table.h
> index db8bfb4..9b5321b 100644
> --- 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(unsigned int nr, 
> uint16_t *st)
>       * 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 btr %1,%0" : "=m" (*st) : "Ir" (nr), "m" (*st));

That's definitely not the right way to fix this - did you read the
description of the change that introduced this? Nevertheless I
admit that change wasn't entirely correct, as it doesn't really allow
the compiler to pick a register (apparently it has been picking an
immediate number for everyone else up to now). I shall send a
proper fix soon.

Jan

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



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