[Vm-dev] Mac PPC Carbon VM resuscitation part 2: status and two questions

[Tim Johnson]

Hi Dave,

On Jul 25, 2020, at 1:57 PM, David T. Lewis wrote:

> Nice to get this update from you, thanks :-)
>
> I cannot answer your specific questions, but here are a couple of
> things that might help.
>
>> Note that my build product, even at
>> 4.7.8, still can't natively launch & interpret a 6505-format image
>> like the release version of 4.6 from files.squeak.org.
>
> I have never actually tested the case of a big-endian interpreter VM
> loading a 6505 image that was saved from a little-endian machine. I  
> tried
> to write the logic around  
> ContextInterpreter>>normalizeFloatOrderingInImage:
> in anticipation of this, but I had no way to test it. So it is very
> possible that I may have gotten something wrong. But I think that I  
> made
> later changes to this logic, so if possible I would prefer to debug
> the problem using a more up to date VMMaker.

OK.  And yes, I saw there were some updates to this functionality over  
time, even through the 4.4 to 4.7 versions of VMMaker.

> You seem to be seeing some problems that may be related to mismatches
> between the VMMaker generated code and the platforms support code.
> In general, there are not a lot of dependencies between the two over
> short time windows, but if you are trying to build with version X of
> the VMMaker sources against version Y of the platform sources from
> the Subversion repository, then things are going to get out of whack
> if the two versions are not reasonably close.
>
> There is no real control around this, but if you are trying to make
> a VM with version X of VMMaker, then you would probably want to check
> out a set of platforms source from Subversion with similar time
> stamp, or from maybe 6 to 12 months earlier.

This is an interesting point.  I had (mistakenly) thought that SVN was  
frozen in time, around the point when the GitHub repo began and (I  
believe) some/all of its history was imported there.

But now that I am looking at the current SVN repo (rather than the  
circa-2010 snapshot fork I'd found elsewhere on GitHub and was using),  
I am finding all kinds of treasures. The files in Glue/image seem  
particularly interesting at first glance.  I had a vague decade-old  
memory that these files existed somewhere.

Now I need to brush up on my SVN skills.  :)

> Overall, you are doing a stepwise progression from the old VM version,
> moving forward one chunk at a time. That is exactly how I would have
> attacked the problem. But with the advantage of my knowing a few  
> things
> about what changed over the years, I would actually suggest that you
> try a short-cut to save some steps. My advice is to set aside your
> stepwise progression for a moment, and try going directly to the
> latest versions of VMMaker and the SVN support code, and see if that
> gets you reasonably close to a working VM. I do not know if this will
> work, but if it does it will save you some time.

Thanks for this.  I'll see what I can do with it.

Tim