On May 12, 2015, at 3:10 AM, marcel.taeumel <Marcel.Taeumel at hpi.de> wrote:

> I think that's only a symptom. Why else is the bug related to different VM
> versions?

I ran into this and various variants of it a little while ago, when I tried to update my somewhat outdated image using the latest Cog VM.  When I ran using an older interpreter VM, the build went fine.

In tracking down one of the MNU failures I was seeing with the Cog build, I saw this:

SmallInteger(Object) >> doesNotUnderstand: #isEmptyOrNil
PluggableListMorphOfMany(PluggableListMorph) >> hasFilter

where:

hasFilter
	^ lastKeystrokes isEmptyOrNil not

the debugger in the context of hasFilter says that lastKeystrokes is an empty ByteString, but when I click on self for the SmallInteger DNU, it says that the receiver is a SmallInteger 0.

Looking at the object context of PluggableListMorphOfMany, I saw that the only SmallInteger 0 value was the instance variable “lastKeystrokeTime” just before “lastKeystrokes”.

So it looks to me like there may be a (rare) instance variable to register mapping bug in the latest Cog VMs.

	— tim