> For more radical changes, we use the SystemTracer.  This writes a clone of a
running (
> !) image onto the disk.  Since it is just writing a file it can make
arbitrary transfo
> rmations on the way to disk.  This is how we changed Squeak from an object-
table to th
> e current direct-pointer object memory format.  More recently Tim Rowledge's
change to
>  the format of compiled methods was done this way.  Having written the new
image, it's
>  a small matter of rewriting and debugging the VM until can run the new image.
Actually, with the simulator, it's even easier. You can design the new VM, work
out what cloner changes are needed, clone an image, run it in simulation, debug
the VM and sometimes the cloning process and get it all working before even
considering generating the C code.
Someday soon, when alan purdy finishes it, you won't even need to generate the
C code...just create obj code directly.

tim

-- 
C:\BELFRY is where I keep my .BAT files.
Tim Rowledge:  rowledge at interval.com (w)  +1 (650) 842-6110 (w)
 tim at sumeru.stanford.edu (h)  <http://sumeru.stanford.edu/tim>