[Vm-dev] BitBltSimulation buffer overrun

karl ramberg karlramberg at gmail.com
Sat Sep 14 04:55:52 UTC 2019


+1

Best,
Karl

On Sat, Sep 14, 2019 at 2:00 AM Ben Coman <btc at openinworld.com> wrote:

>
> Thats a great result Nicolas, after its been outstanding for so long.
>
> + bbW <= startBits
> - bbW < startBits
> + preload := bbW > startBits and: [(m1 bitAnd: mask1) ~= mask1]. "i.e.
> there are some missing bits"
> - preload := (m1 bitAnd: mask1) ~= mask1. "i.e. there are some missing
> bits"
>
> I nominate you for the Charles Steinmetz Chalk Mark Medal...
> https://playingintheworldgame.com/2014/07/19/the-chalk-mark/
>
> cheers -ben
>
>
> On Sat, 14 Sep 2019 at 03:03, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
>
>>
>> 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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