[Vm-dev] Primitive table support for running older images

[David T. Lewis]

On Thu, Dec 22, 2016 at 09:10:05PM -0300, Jecel Assumpcao Jr. wrote:
>  
> Bert Freudenberg wrote on Thu, 22 Dec 2016 16:40:51 +0100
> > In SqueakJS I have a single flag??oldPrims??to switch between two set of primitives.
> > This appears to work fine all the way back to Squeak 1.x. The flag is set based on
> > whether the image format has closures or not.
> 
> I had the impression, based on some difficulties on getting the
> simulator to work (around 2008, I think), that at one point an instance
> variable in a key class (Process, most likely) stopped being used and
> then a few versions later it got reused in a different way. This also
> happened to a numbered primitive or two. And the version number stayed
> 6502 though all these changes. So a newer VM would appear to run an
> older image just fine but once in a while you got a really strange
> crash.
> 
> My hope is that this was just some horrible nightmare of mine and not
> actual memories, but I will have to take some time searching through old
> email messages to be sure.
> 

The other thing that I expect may be a source of trouble is the special
objects array. But I have not actually checked to see if it's a problem yet.

It is quite encouraging that SqueakJS is able to run all the way back to
Squeak 1.x with just two variations of the primitive table.

Dave