Emacs 21.2 core dump in find_first_unchanged_at_end_row

[Paul Eggert]

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In GNU Emacs 21.2.1 (sparc-sun-solaris2.8, X toolkit, Xaw3d scroll bars)
 on sic.twinsun.com
configured using `configure  --prefix=/opt/reb --with-gcc --with-pop 
--x-includes=/opt/sfw/include:/usr/openwin/include 
--x-libraries=/opt/sfw/lib:/usr/openwin/lib'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

This one is hard to describe.  I had edited using Emacs for quite
some time, and and just saved a file.  I was starting to do something
else (sorry, can't remember what), and Emacs dumped core.

Here is a GDB backtrace of the core dump:

#0  0xfed9c840 in ?? ()
#1  0xfed9b86c in ?? ()
#2  0x000d866c in abort () at emacs.c:387
#3  0x00064aa8 in find_first_unchanged_at_end_row (w=0xb97, delta=0xffbedd24, 
    delta_bytes=0xffbedd20) at xdisp.c:11169
#4  0x00065240 in try_window_id (w=0xb3e800) at xdisp.c:11585
#5  0x00062f74 in redisplay_window (window=1085532160, just_this_one_p=0)
    at xdisp.c:10237
#6  0x0005f9d8 in redisplay_windows (window=1085532160) at xdisp.c:9224
#7  0x0005e8dc in redisplay_internal (preserve_echo_area=4909056)
    at xdisp.c:8828
#8  0x000de2e0 in read_char (commandflag=1, nmaps=2, maps=0xffbee968, 
    prev_event=271256580, used_mouse_menu=0xffbee9f0) at keyboard.c:2272
#9  0x000e54b8 in read_key_sequence (keybuf=0xffbeeb28, bufsize=30, 
    prompt=271256580, dont_downcase_last=0, can_return_switch_frame=1, 
    fix_current_buffer=1) at keyboard.c:8180
#10 0x000db378 in command_loop_1 () at keyboard.c:1440
#11 0x0013cecc in internal_condition_case (bfun=0xdb114 <command_loop_1>, 
    handlers=271378628, hfun=0xdac7c <cmd_error>) at eval.c:1267
#12 0x000dafa4 in command_loop_2 () at keyboard.c:1245
#13 0x0013ca34 in internal_catch (tag=271330980, 
    func=0xdaf80 <command_loop_2>, arg=271256580) at eval.c:1030
#14 0x000daf30 in command_loop () at keyboard.c:1224
#15 0x000da9e8 in recursive_edit_1 () at keyboard.c:950
#16 0x000dab44 in Frecursive_edit () at keyboard.c:1006
#17 0x000d9908 in main (argc=0, argv=0xffbef06c, envp=0x197c00) at emacs.c:1547

Here are some variable values that may help you diagnose the problem.
Emacs aborted because row->enabled_p is zero.

(gdb) p row->enabled_p
$4 = 0
(gdb) p first_text_row
$5 = (struct glyph_row *) 0xba3000
(gdb) p row
$6 = (struct glyph_row *) 0xba4634
(gdb) p row - first_text_row
$7 = 49
(gdb) p last_unchanged_pos
$8 = 33554432
(gdb) p last_unchanged_pos_old 
$9 = 4223
(gdb) p *delta
$10 = 1
(gdb) p *delta_bytes
$11 = 1
(gdb) p Z_old
$12 = 4223
(gdb) p Z_BYTE_old
$13 = 8158
(gdb) p *row
$14 = {glyphs = {0xb96000, 0xb96000, 0xb966b8, 0xb966b8}, used = {0, 22, 0}, 
  x = 0, y = 936, pixel_width = 154, ascent = 11, height = 13, 
  phys_ascent = 11, phys_height = 13, visible_height = -13, hash = 76364866, 
  start = {pos = {charpos = 4643, bytepos = 4643}, overlay_string_index = -1, 
    string_pos = {charpos = -1, bytepos = -1}, dpvec_index = -1}, end = {
    pos = {charpos = 4665, bytepos = 4665}, overlay_string_index = -1, 
    string_pos = {charpos = -1, bytepos = -1}, dpvec_index = -1}, 
  enabled_p = 0, inverse_p = 0, truncated_on_left_p = 0, 
  truncated_on_right_p = 0, overlay_arrow_p = 0, continued_p = 0, 
  displays_text_p = 1, ends_at_zv_p = 0, fill_line_p = 0, 
  indicate_empty_line_p = 0, contains_overlapping_glyphs_p = 0, 
  full_width_p = 0, mode_line_p = 0, overlapped_p = 0, 
  ends_in_middle_of_char_p = 0, starts_in_middle_of_char_p = 0, 
  overlapping_p = 0, mouse_face_p = 0, ends_in_newline_from_string_p = 0, 
  continuation_lines_width = 0}