Re: [Xen-devel] [PATCH] x86: use gcc6'es flags asm() output support

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 02/08/16 07:09, Jan Beulich wrote:
>>>> On 01.08.16 at 19:11, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 01/08/16 17:06, Jan Beulich wrote:
>>>>>> On 01.07.16 at 18:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> How about a different example, from the second hunk
>>>>
>>>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>>>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>>>> @@ -832,8 +832,19 @@ static int read_ulong(
>>>>  static bool_t mul_dbl(unsigned long m[2])
>>>>  {
>>>>      bool_t rc;
>>>> -    asm ( "mul %1; seto %2"
>>>> -          : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
>>>> +
>>>> +    asm ( "mul %1;"
>>>> +#ifndef __GCC_ASM_FLAG_OUTPUTS__
>>>> +          "seto %[rc];"
>>>> +#endif
>>>> +          : "+a" (m[0]), "+d" (m[1]),
>>>> +#ifdef __GCC_ASM_FLAG_OUTPUTS__
>>>> +            [rc] "=@cco" (rc)
>>>> +#else
>>>> +            [rc] "=qm" (rc)
>>>> +#endif
>>>> +        );
>>>> +
>>>>      return rc;
>>>>  }
>>> Looking at this again I think I really like the original, submitted version
>>> better. Are you strongly biased towards the above form?
>> I am not overly fussed between this version and the original submission.
>>
>> However, I definitely think that we shouldn't hide semantic bits of the
>> ASM statement behind macros.
> Well, the originally submitted variant doesn't do anything like that,
> so may I translate the above to an ack?

You do already have a Rev-by from my first reply.

~Andrew

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