Re: MPS: Loaded pdump

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Ok, I think I'll try to get rid of the pdump root. Maybe I'll regret it,
and maybe I'll fail, but I feel the root is not the right thing to have.
(I'll do in in a branch from the branch in the fork here.)

Step 1:

Make the loaded dump traversable by dumping igc_headers.

How easy or not that is is hard to say. On one hand, there seems to be
dump_object_begin, which looks promising, but I already know one case
(hash tables), where extending that function to write igc_headers might
not be sufficient. And where is one exception there are more. And flags
like pack_objects could interfere, and so on.

Doenside: igc_header is then even more set in stone. Removing the header
for conses becomes even more work. One would need a new section in the
dump, just for conses.

Step 1.5:

When (1) is done, one could make the dump an exact root and use
dflt_scan on it. (That's better than an ambig root, but I don't want the
root because the world is stopped when roots are scanned.)

Step 2:

Walk through the dump and make copies of dumped objects in MPS memory.
Record a mapping from dumped -> MPS object. Then walk through the copied
objects and replace references to dumped objects.

This is a bit hand-wavy. At some point when a dump is loaded, things in
Emacs are set up to refer to objects in the dump. We will have to do our
copy before that and somehow make sure the copy is used instead of the
dump.

Unmap the dump, remove the root.

WDYT?