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SubjectRe: Bug in herd7 [Was: Re: Litmus test for question from Al Viro]
> 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.

--Luc

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