[Vm-dev] BitBltSimulation buffer overrun

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Wed Sep 4 19:24:13 UTC 2019

Le mer. 4 sept. 2019 à 20:16, tim Rowledge <tim at rowledge.org> a écrit :

> > On 2019-09-04, at 11:00 AM, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
> >
> > tim
> > Do we ever use the extra word that we read? I don't think so, we don't
> generate funny artefacts.
> > But we could try and test that now that we know how to trigger it
> (statistically).
> We certainly shouldn't use that extra word.
> Unless something has gone horribly wrong, the only time this is an issue
> is on the last fetch of the last row of a BLT. So we *could* consider
> splitting out the last row and only for that last row include a check for
> the last word, and only for that word include a 'stick 0 in'.
> Yes, possibly, but then one also has to check the first row whenever vDir
= -1 (checkSourceOverlap).
I said a hell of a stateful branchful code, but you know it even better
than I ;)

Since this is an assert for the debug, perhaps the smart thing to do is
> make the assert test more thoughtful in some manner. The typical case
> simply doesn't matter, since all we do is load a wasted word. Where things
> do need some care is at the end of object memory and page boundaries etc.
> tim
> --
> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> No single raindrop believes it is to blame for the flood
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