Re: mark_object crash in 22.1 and latest CVS (as of tonight)

[Richard Stallman]

Nothing gets "removed" from the undo list in normal use.  It gets
truncated, which drops off elements at the end, but other than that
all that normally happens is that editing operations add elements.

Markers in the list should not become free, because the undo list
itself should preserve them from GC.

If this is reproducible, can you put a breakpoint at Fgarbage_collect
and examine the data just before the GC which gets this crash?
Examine that list using the x... commands, and see if that marker
is already free.

    Looking harder at the code, I'm convinced that the undo_list should come 
before
    the name entry in the buffer structure,

Definitely not.  It needs to be AFTER `name' so that it will be marked
by GC.

    Anyone know what the elements of the undo_list mean?  Some are conses
    with a marker
    in their CAR and a number in their CDR, some are just conses of two
    numbers and some
    are conses of a string and a number.

The Lisp Manual documents these.  Node `Undo'.