[PATCH 2/4] include: Implement __stosb compiler intrinsic.

[Rémi Bernon]

On 9/13/21 7:00 PM, Zebediah Figura wrote:
> On 9/13/21 11:53 AM, Rémi Bernon wrote:
>> On 9/13/21 6:42 PM, Zebediah Figura wrote:
>>> On 9/13/21 10:25 AM, Rémi Bernon wrote:
>>>> On 9/13/21 4:51 PM, Piotr Caban wrote:
>>>>> Hi Rémi,
>>>>>
>>>>> On 9/13/21 2:23 PM, Rémi Bernon wrote:
>>>>>> +static inline void __stosb(unsigned char* dst, unsigned char c,
>>>>>> size_t n)
>>>>>> +{
>>>>>> +    __asm__ __volatile__ ("cld; rep; stosb" : "=D"(dst) : "a"(c),
>>>>>> "D"(dst), "c"(n) : "memory", "cc");
>>>>>> +}
>>>>> I don't know if it's important here but Microsoft's i386 cdecl abi
>>>>> specifies direction flag value on function call. Maybe if __cdecl is
>>>>> added cld call may be removed.
>>>>>
>>>>
>>>> All the ABIs are apparently requiring it to be cleared before a 
>>>> function
>>>> call, or am I missing something? So it looks like it's not needed
>>>> anywhere and I was just over cautious.
>>>>
>>>
>>> Well, ABIs do, but you're not defining that as an asm function; you're
>>> using inline assembly. So you can't guarantee anything.
>>>
>>
>> But it's wrapped in a function, which implies what its calling
>> convention ABI implies?
>>
> 
> No, not really. The compiler is free to insert whatever assembly it 
> wants before and after the __asm__ block, as long as it satisfies the 
> constraints.
> 
> Not only that, but because it's a static function, the compiler is also 
> free not to give it a standard calling convention at all.
> 

Well, anyway MSVC doesn't generate cld with this intrinsic so I think we 
should not either.
-- 
Rémi Bernon <rbernon at codeweavers.com>