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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew

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