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

[Zebediah Figura]

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.