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

[Richard Guenther]

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.

Richard.