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From: Richard Stallman <rms@gnu.org>
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Subject: Re: unpredictable emacs 21 crashes
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    (gdb) up
    #1  0x80d6044 in fatal_error_signal ()
    (gdb) up
    #2  <signal handler called>
    (gdb) up
    #3  0x811d476 in mark_object ()
    (gdb) up

This is a failure in GC.  It is natural that there would be many stack
frames recursively calling mark_object.  To find where GC was called,
try moving up the stack many frames at once.  Use `up 100' for
instance.  Try various numbers; do a binary search.

Most likely, whatever called GC won't be relevant.
The crash is probably due to invalid data.  To analyze it
you need to study the data being worked on in the innermost frames.
By working back one frame at a time, you can see what data structure
the invalid objects are found in.  The vector last_marked (see
alloc.c) can help you trace this back.

Once you see if there is a pattern to that, we might have an idea
where to look for the real problem.

This analysis process is nontrivial, but there's no shortcut
except to be very very lucky.