[Vm-dev] BitBltSimulation buffer overrun

[Nicolas Cellier]

Hehe, I think I fixed it in VMMaker.oscog-nice.2563
The ultimate tool for understanding and debugging this was pen and paper!
I don't know how young techies will do ;)



Le mer. 4 sept. 2019 à 21:24, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

>
>
>
> 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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