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

[Richard Stallman]

    I've done some more experiments; it occurred to me that if the marker in the
    undo list was gc-marked already when we got to the special processing, then
    it would be skipped.

I looked to see what you mean, and I see that some elements do get
removed from the undo list.  I hadn't remembered that -- sorry.

Is this the special processing you mean?

        /* If a buffer's undo list is Qt, that means that undo is
           turned off in that buffer.  Calling truncate_undo_list on
           Qt tends to return NULL, which effectively turns undo back on.
           So don't call truncate_undo_list if undo_list is Qt.  */
        if (! EQ (nextb->undo_list, Qt))
          {
          ...

If so, it is supposed to delete elements for markers
that weren't already marked by GC.  And then it marks the undo
list in the normal way.

Does it look like that code failed to remove an element
which was supposed to update a marker?

Was the marker already corrupted (replaced with Lisp_Misc_Free)
before the start of the loop?