Re: Emacs 21.2 core dump in find_first_unchanged_at_end_row

[Paul Eggert]

> From: gerd.moellmann@t-online.de (Gerd Moellmann)
> Date: 29 Mar 2002 11:20:40 +0100

> > I do remember one other thing.  Right after I saved the file, I must
> > have accidentally typed one more "a" character into the buffer at a
> > relatively random location in the file.  This caused emacs to create a
> > "#" file with the extra "a" in it, which I found after the core dump.
> > I think this must have happened just before Emacs dumped core.
> 
> IIRC, the last time something like that came up, it was caused by
> bogus unchanged information in the buffer
> (BEG_UNCHANGED/END_UNCHANGED).  Maybe it's worth looking at that,
> although it might be hard to reconstruct what happened.

Thanks.  Unfortunately I know little about this area.  To illustrate
my naivete, can I ask a couple of questions?  Why can dispnew.c's
direct_output_for_insert get away with modifying BEG_UNCHANGED but not
END_UNCHANGED?  Is it possible that direct_output_for_insert was
called during the scenario that I describe ("C-x C-s" immediately
followed by "a")?

Also, I can run 'gdb' and print things if you like.  For example:

#3  0x00064aa8 in find_first_unchanged_at_end_row (w=0xb97, delta=0xffbedd24, 
    delta_bytes=0xffbedd20) at xdisp.c:11169
(gdb) p current_buffer->text[0]
$8 = {
  beg = 0x1eb9478 "[some long and boring text that is not relevant to the bug, 
I 
hope...........................................................................................................................................]"...,
 
  gpt = 4139, z = 8159, gpt_byte = 4139, z_byte = 8159, gap_size = 1073, 
  modiff = 6648, save_modiff = 6647, overlay_modiff = 5544, 
  beg_unchanged = 4137, end_unchanged = 3936, unchanged_modified = 6647, 
  overlay_unchanged_modified = 5544, intervals = 0x0, markers = 541792076}

Unfortunately the text itself is part of some private correspondence,
and I can't simply give you the core file.