While running an assert or debug VM, I noticed repeated logs in console:

(((usqInt)sourceIndex)) < endOfSource 2132

This corresponds to failing assert: in BitBltSimulation slang

srcLongAt: idx <inline: #always> self assert: idx asUnsignedInteger < endOfSource. ^self long32At: idx

It is easily reproducible with this Squeak test:

BitmapStreamTests new testShortIntegerArrayReadRefStream2.

Such read past end is benign, except in rare case when we read past a page boundary and cause a SEGV!

Via LLDB or via VM SImulation, we can find that it is related to the case when we `preload `a word from source and next source word because we think that we need more than 1 source word to fill 1st dest word.

I have identified and hopefully fixed the bug in VMMaker.oscog-nice.2563 https://source.squeak.org/VMMaker/VMMaker.oscog-nice.2563.diff