[PATCH, i386]: Emit cld instruction when stringops are used

[Chris Lattner]

On Mar 6, 2008, at 12:56 PM, Richard Guenther wrote:

> On Thu, Mar 6, 2008 at 6:29 PM, Chris Lattner <clattner@apple.com>  
> wrote:
>>> No, gcc was never doing that, and there is no point to start doing
>>> that.
>>> If inline asm thinks it can't trust the psABI, it has to do cld on
>>> its own.
>>> And AFAIK inline asm that uses stos*/movs* etc. typically has cld at
>>> the
>>> beginning.  If inline asm uses std, it must do cld before returning
>>> back to
>>> compiler generated code (again, from what I've seen asm that uses  
>>> std
>>> has the corresponding cld too).
>>
>> You forget that there is a ton of code in the world that does:
>>
>> void foo() {
>>   asm ( " rep; movsb", ...)
>> }
>>
>> Knowing that the direction flag is clear on entry to the function.
>> You propose auditing all the *existing* inline asm code active in the
>> world?  I thought the issue here was that *user* space can't trust
>> that the direction flag is clear because of the kernel bug: if so,
>> this isn't just about inline asm in the kernel.
>
> Such code was broken in the past anyway, no need to try to fix that  
> now.

How so?

-Chris