On Mon, Oct 05, 2020 at 05:15:57PM +0200, Luc Maranget wrote:
> > On Sun, Oct 04, 2020 at 12:16:31AM +0900, Akira Yokosawa wrote:
> > > Hi Alan,
> > >
> > > Just a minor nit in the litmus test.
> > >
> > > On Sat, 3 Oct 2020 09:22:12 -0400, Alan Stern wrote:
> > > > To expand on my statement about the LKMM's weakness regarding control
> > > > constructs, here is a litmus test to illustrate the issue. You might
> > > > want to add this to one of the archives.
> > > >
> > > > Alan
> > > >
> > > > C crypto-control-data
> > > > (*
> > > > * LB plus crypto-control-data plus data
> > > > *
> > > > * Expected result: allowed
> > > > *
> > > > * This is an example of OOTA and we would like it to be forbidden.
> > > > * The WRITE_ONCE in P0 is both data-dependent and (at the hardware level)
> > > > * control-dependent on the preceding READ_ONCE. But the dependencies are
> > > > * hidden by the form of the conditional control construct, hence the
> > > > * name "crypto-control-data". The memory model doesn't recognize them.
> > > > *)
> > > >
> > > > {}
> > > >
> > > > P0(int *x, int *y)
> > > > {
> > > > int r1;
> > > >
> > > > r1 = 1;
> > > > if (READ_ONCE(*x) == 0)
> > > > r1 = 0;
> > > > WRITE_ONCE(*y, r1);
> > > > }
> > > >
> > > > P1(int *x, int *y)
> > > > {
> > > > WRITE_ONCE(*x, READ_ONCE(*y));
> > >
> > > Looks like this one-liner doesn't provide data-dependency of y -> x on herd7.
> >
> > You're right. This is definitely a bug in herd7.
> >
> > Luc, were you aware of this?
>
> Hi Alan,
>
> No I was not aware of it. Now I am, the bug is normally fixed in the master branch of herd git deposit.
> <https://github.com/herd/herdtools7/commit/0f3f8188a326d5816a82fb9970fcd209a2678859>
>
> Thanks for the report.
Thank you very much, Luc! I will rebuild and give it a try.
Thanx, Paul
