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

[Richard Stallman <rms@gnu.org>]

      I assumed
    someone would recognize WHAT part of a buffer from the contents of the,
    list, a mixture of conses with marker-in-no-buffer in the car of some and
    Lisp_Misc_Free  in the car of others, the cdr's being negative numbers
    of pretty small absolute magnitude.

I didn't see that when I looked at the other message.  Can anyone
guess what data this is?

    > Once you answer those, you can try to figure out how it happened
    > that the data structure ended up with a bad pointer.
    > Maybe GC failed to mark that pointer, so the misc object got freed
    > even though it was still in use.

    Are there any tools to help with this, e.g. an allocation trace or GC trace?
    I'm afraid this is the first time I've looked at the Emacs src code.

The x... GDB commands in .gdbinit are useful for examining data
structures during GC.

`last_marked' and `last_marked_index' keep track of the sequence of
data objects that were marked.  You can use that to determine precisely
how the bad data was reached.