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

Jakub Jelinek
2008-03-06T09:02:52Z

On Thu, Mar 06, 2008 at 09:44:05AM +0100, Andi Kleen wrote:
> "H. Peter Anvin" <hpa@zytor.com> 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.
>
> 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.

Jakub