Re: SIGSEGV in garbage collection

[Richard Stallman]

    >     | #0  0x8116dae in mem_delete_fixup (x=0x826bc80) at alloc.c:3043
    >     | #1  0x8116d40 in mem_delete (z=0x9247ad8) at alloc.c:3012
    >     | #2  0x8114e8b in lisp_free (block=0x9247ab0) at alloc.c:632
    >
    > The first question is, what's going on in those frames?
    > Can you find the invalid data and see what is invalid about it?

    I have no idea how to find the invalid data.

First you look at the source code in those functions, and see what
data is being accessed.  Then you look at the values and see if they
are correct.  That's how you debug.

This entails looking at the text that defines the data structure and
understanding what it should look like if it is consistent.  Then
examining the real data and seeing what's inconsistent in it.

You do it starting with the innermost frame and work outward (at the
same time working back in time, deducing facts about earlier events).

    I had quite a lot of frames opened: *info*, a Perl-Script, *scratch*,
    *Message*, a Makefile, and a *Summary* buffer of Gnus.

That doesn't shed any light on the problem.  There is no reason to
suppose any part of this is directly relevant.