On Tue, Aug 23, 2016 at 11:21 AM, marcel.taeumel <Marcel.Taeumel@hpi.de> wrote:

Hi, there.

It is, unfortunately, not possible to turn back time and rewrite history. ;-)

... unless we're dealing with software. Oh wait, we are ;)

There is several important code that makes excessive use of instVar
accesses such as in SystemProgressMorph or HandMorph. Making any change in
their class layout while using some of their methods will provoke a strange
error. This could only be changed by a VM that keeps old class
layouts/schemata around for some longer time until there is no old compiled
method on any stack anymore.

Class layout changes and instance migration is handled fully in the image by class ClassBuilder. The VM is not at fault here.

Usually, restarting the update process helps here. There is no way to fix
that in order to interactively update from 5.0 to 5.1 without any errors.

We can retroactively change the config map that introduced the problem. I'm certain it would be possible to fix, but I am not entirely sure it's worth the trouble.

- Bert -