Xen devel - Mar 2012 - [PATCH] x86: Fix grant-table build error

Fixes build error with btrw instruction.

xen-unstable/xen/include/asm/grant_table.h:57: 
Error: Incorrect register `%edx'' used with `w'' suffix

Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
---
 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));
 }
 
 /* Foreign mappings of HHVM-guest pages do not modify the type count. */
-- 
1.7.2.5

>>> On 22.03.12 at 16:21, Lin Ming <mlin@ss.pku.edu.cn> 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@ss.pku.edu.cn>
> ---
>  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. */

On Thu, Mar 22, 2012 at 11:41 PM, Jan Beulich <JBeulich@suse.com>
wrote:
>>>> On 22.03.12 at 16:21, Lin Ming <mlin@ss.pku.edu.cn>
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?
# gcc --version
gcc (Debian 4.4.5-8) 4.4.5
>
>> Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
>> ---
>>  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.
I''d like to test it.

Lin Ming