SEGFAULT on increment_row_positions

[JD Smith]

My programming mode IDLWAVE tends to trigger many more SEGFAULTS in
Emacs 21 than any other use of Emacs I make, but only when the IDL
shell is running as a subprocess under Comint.  In particular, when
the IDL sub-process gets quite large (IDL is a data processing
language), the SEGFAULTS seem more common, which may indicate a
garbage collection or other memory related bug (just guessing here).
I have managed today to achieve a SEGFAULT after every 10-30min of
heavy use, and found this trace:

Program received signal SIGSEGV, Segmentation fault.
0x0804fdf8 in increment_row_positions (row=0x86905a4, delta=-17, delta_bytes=4)
    at dispnew.c:1188
1188          if (BUFFERP (row->glyphs[area][i].object)
(gdb) xbacktrace
(gdb) bt
#0  0x0804fdf8 in increment_row_positions (row=0x86905a4, delta=-17,
    delta_bytes=4) at dispnew.c:1188
#1  0x0804fe7b in increment_matrix_positions (matrix=0x8a771b0, start=56,
    end=86, delta=-17, delta_bytes=-17) at dispnew.c:927
#2  0x0806b0dc in try_window_id (w=0x84b3a90) at xdisp.c:11883
#3  0x0806fe14 in redisplay_window (window=1212889744, just_this_one_p=1)
    at xdisp.c:10260
#4  0x08072334 in redisplay_internal (preserve_echo_area=4) at xdisp.c:8910
#5  0x0805710d in sit_for (sec=0, usec=100000, reading=0, display=1,
    initial_display=1) at dispnew.c:6230
#6  0x080e8f0b in command_loop_1 () at keyboard.c:1687
#7  0x0813704d in internal_condition_case (bfun=0x80e891d <command_loop_1>,
    handlers=405408900, hfun=0x80e1ca8 <cmd_error>) at eval.c:1267
#8  0x080dd899 in command_loop_2 () at keyboard.c:1245
#9  0x08136f6c in internal_catch (tag=4, func=0x80dd876 <command_loop_2>,
    arg=405312556) at eval.c:1030
#10 0x080dd6a5 in command_loop () at keyboard.c:1224
#11 0x080dd742 in recursive_edit_1 () at keyboard.c:950
#12 0x080dd85f in Frecursive_edit () at keyboard.c:1006
#13 0x080dcb44 in main (argc=3, argv=0xbffff494, envp=0xbffff4a4)
    at emacs.c:1547 #14 0x40309e23 in __libc_start_main () from
/lib/tls/libc.so.6 #15 0x0804f451 in ?? ()

This is GNU Emacs 21.3.1 (i386-redhat-linux-gnu, X toolkit, Xaw3d
scroll bars) of 2005-02-04 on bugs.build.redhat.com running under FC3.

Any hints on pursuing this further?

These variable printouts may be of use:

(gdb) p i
$1 = 1
(gdb) p area
$2 = 1
(gdb) p row->glyphs[area][i]
$3 = {
  charpos = 3899,
  object = 1213660376,
  pixel_width = 10,
  voffset = 0,
  type = 0,
  multibyte_p = 1,
  left_box_line_p = 0,
  right_box_line_p = 0,
  overlaps_vertically_p = 0,
  padding_p = 0,
  glyph_not_available_p = 0,
  face_id = 10,
  u = {
    ch = 32,
    cmp_id = 32,
    img_id = 32,
    stretch = {
      height = 32,
      ascent = 0
    },
    val = 32
  }
}

I'll keep trying, to see where the SEGFAULT is typically occurring.

Thanks,

JD