[Vm-dev] [squeak-dev] Bug in PolygonMorph>>#filledForm

[Nicolas Cellier]

There's already a problem with end 2018 VM
VM [CoInterpreterPrimitives VMMaker.oscog-eem.2488] 5.0.201812040127

Le ven. 21 févr. 2020 à 22:48, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

> Interesting case to debug...
> In 64bits VM, a problem first appears in first smear:distance: operation
> (direction 1 at 0 to the right) at skew=16...
>
> [image: Capture d’écran 2020-02-21 à 22.24.03.png]
>
>
> It seems that we copy bits too far to the right (hence we overwrite the
> bottom rows)
> Fortunately, the artefacts outside polygon bounds disappear at final
> bitAnd operation, but that's scary!
>
> It could be:
> - case of overlap detection failure (#checkSourceOverlap), but the code
> did not change
> - bad initialisation in #sourceSkewAndPointerInit (the one I corrected in
> 2019)
>  https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/426
> - bug in #copyLoop (which I also corrected in 2019)
> https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/441
>
> Weird kind of integer overflow? (I've made most of the int unsigned, so
> this might not be detected by UB sanitizer).
>
> Or could it be that the extra buffer overrun that I removed did have a
> side effect of filling more gaps?
> It would be interesting to observe what happens at same #smear:distance:
> step with older VM.
>
> Le ven. 21 févr. 2020 à 20:39, Stéphane Rollandin <lecteur at zogotounga.net>
> a écrit :
>
>> > Hmmm... the form was still filled in Squeak 5.1 (Update 16549),
>> > VM 201701311639 (32-bit). Not so in Squeak 5.2.
>>
>> Yes, but that same 5.1 image with a current VM has the problem...
>>
>> Stef
>>
>>
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