Re: RELEASE BLOCKER: Linux doesn't follow x86/x86-64 ABI wrt direction flag

[H. Peter Anvin]

Jakub Jelinek wrote:
> On Thu, Mar 06, 2008 at 09:44:05AM +0100, Andi Kleen wrote:
> > "H. Peter Anvin" <hpa@xxxxxxxxx> writes:
> >
> > > Richard Guenther wrote:
> > > > We didn't yet run into this issue and build openSUSE with 4.3 since
> > > > more than
> > > > three month.
> > > Well, how often do you take a trap inside an overlapping memmove()?
> > That was the state with older gcc, but with newer gcc it does not necessarily
> > reset the flag before the next function call.

If so, that's a much worse bug.

> > so e.g. if you have
> >
> >         memmove(...)
> >         for (... very long loop .... ) {
> >                 /* no function calls */
> >                 /* signals happen */
> >         }
> >
> > the signal could see the direction flag
>
> memmove is supposed to (and does) do a cld insn after it finishes the
> backward copying.

You can still take a signal inside memmove() itself, of course.

	-hpa
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