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

[Lin Ming <mlin@xxxxxxxxxxxxx>]

On Thu, Mar 22, 2012 at 11:41 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> 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?

# gcc --version
gcc (Debian 4.4.5-8) 4.4.5

>
>> 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.

I'd like to test it.

Lin Ming

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