bug#22526: 25.0.90; Crash starting gnus

[Andy Moreton <andrewjmoreton@gmail.com>]

On Sun 07 Feb 2016, Eli Zaretskii wrote:

>> From: Andy Moreton <andrewjmoreton@gmail.com>
>> Date: Sun, 07 Feb 2016 20:58:57 +0000
>>
>> On Sun 07 Feb 2016, Eli Zaretskii wrote:
>> > Hard to tell without a reproducible recipe, or at least some
>> > additional info.  If the session is still running in a debugger, I
>> > might ask some questions about some variables.
>>
>> I don't have that session running any more. Please do make suggestions
>> for things to look at in gdb that I can try if I manage to reproduce the
>> problem.
>
> Thanks.
>
> AFAIU, the crash was here:
>
>   /* Put an anchor.  */
>   *(Z_ADDR) = 0;  <<<<<<<<<<<<<<<<<
>
> So the first question is, of course, what is the value of Z_ADDR?
>
> Next question is what are the values of the variables in the
> expression to which Z_ADDR expands:
>
>   /* Address of end of buffer.  */
>   #define Z_ADDR (current_buffer->text->beg + current_buffer->text->gap_size + current_buffer->text->z_byte - BEG_BYTE)

I've seen a similar crash again with emacs-25 built from changeset 456c0a31.

Lisp Backtrace:
"internal-default-process-filter" (0xbf2248)
"accept-process-output" (0xbf3940)
"nnheader-accept-process-output" (0xbf41e0)
"nntp-accept-process-output" (0xbf4a70)
"nntp-send-command-nodelete" (0xbf5320)
"nntp-send-xover-command" (0xbf5bb0)
"nntp-retrieve-headers-with-xover" (0xbf6470)
0x9dab1b8 PVEC_COMPILED
"nntp-with-open-group-function" (0xbf75b0)
"nntp-retrieve-headers" (0xbf7e40)
"gnus-retrieve-headers" (0xbf86d0)
"gnus-cache-retrieve-headers" (0xbf8f70)
"gnus-retrieve-headers" (0xbf9800)
"gnus-fetch-headers" (0xbfa0a0)
"gnus-select-newsgroup" (0xbfa950)
"gnus-summary-read-group-1" (0xbfb1f0)
"gnus-summary-read-group" (0xbfbaa0)
"gnus-summary-next-group" (0xbfc350)
"gnus-summary-walk-group-buffer" (0xbfcc10)
"gnus-summary-next-article" (0xbfd4b0)
"gnus-summary-next-unread-article" (0xbfdd50)
"gnus-summary-next-page" (0xbfe740)
"funcall-interactively" (0xbfe738)
"call-interactively" (0xbfebf0)
"command-execute" (0xbff488)

The C backtrace from "bt full" starts with the frames below (details of
current_buffer follow):

#1  0x000000040028fbc4 in emacs_abort () at ../../src/w32fns.c:9794
        button = 0x6
#2  0x000000040012f72b in terminate_due_to_signal (sig=0xb, backtrace_limit=0x28) at ../../src/emacs.c:380
No locals.
#3  0x000000040015da9d in handle_fatal_signal (sig=0xb) at ../../src/sysdep.c:1601
No locals.
#4  0x000000040015da6d in deliver_thread_signal (sig=0xb, handler=0x40015da85 <handle_fatal_signal>) at ../../src/sysdep.c:1575
        old_errno = 0xc
#5  0x000000040015dad9 in deliver_fatal_thread_signal (sig=0xb) at ../../src/sysdep.c:1613
No locals.
#6  0x0000000400301540 in _gnu_exception_handler (exception_data=0xbf1040) at C:/repo/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crt_handler.c:223
        old_handler = <optimized out>
        action = 0x0
        reset_fpu = 0x0
#7  0x00007ff901ae5ac6 in ntdll!__C_specific_handler () from C:\WINDOWS\SYSTEM32\ntdll.dll
No symbol table info available.
#8  0x00007ff901af9a9d in ntdll!.chkstk () from C:\WINDOWS\SYSTEM32\ntdll.dll
No symbol table info available.
#9  0x00007ff901a84f29 in ntdll!RtlImageNtHeaderEx () from C:\WINDOWS\SYSTEM32\ntdll.dll
No symbol table info available.
#10 0x00007ff901af8baa in ntdll!KiUserExceptionDispatcher () from C:\WINDOWS\SYSTEM32\ntdll.dll
No symbol table info available.
#11 0x000000040017202c in make_gap_larger (nbytes_added=0x1000) at ../../src/insdel.c:411
        tem = {
          i = 0xd510
        }
        real_gap_loc = 0xf035
        real_gap_loc_byte = 0xf035
        old_gap_size = 0x7d0
        current_size = 0xf804
#12 0x00000004001723e4 in make_gap (nbytes_added=0x830) at ../../src/insdel.c:481
No locals.
#13 0x00000004001733a4 in insert_from_string_1 (string=..., pos=0x0, pos_byte=0x0, nchars=0x1000, nbytes=0x1000, inherit=0x0, before_markers=0x1) at ../../src/insdel.c:916
        outgoing_nbytes = 0x1000
        intervals = 0xbf1fd0
#14 0x00000004001731f3 in insert_from_string_before_markers (string=..., pos=0x0, pos_byte=0x0, length=0x1000, length_byte=0x1000, inherit=0x0) at ../../src/insdel.c:882
        opoint = 0xf035
#15 0x000000040025011d in Finternal_default_process_filter (proc=..., text=...) at ../../src/process.c:5527
        old_read_only = {
          i = 0x0
        }
        old_begv = 0x1
        old_zv = 0xf035
        old_begv_byte = 0x1
        old_zv_byte = 0xf035
        before = 0xf035
        before_byte = 0xf035
        opoint_byte = 0xf035
        b = 0xbf20e0
        p = 0x77feb88
        opoint = 0xf035
#16 0x00000004001eb021 in Ffuncall (nargs=0x3, args=0xbf2240) at ../../src/eval.c:2696
        internal_argbuf = {{
            i = 0xbf21f0
          }, {
            i = 0x400163f98
          }, {
            i = 0x0
          }, {
            i = 0x0
          }, {
            i = 0xbf21b0
          }, {
            i = 0x40012990e
          }, {
            i = 0x401b9b350
          }, {
            i = 0x401ba2dd0
          }}
        fun = {
          i = 0x4006a8df5
        }
        original_fun = {
          i = 0x7ee0
        }
        funcar = {
          i = 0x0
        }
        numargs = 0x2
        lisp_numargs = {
          i = 0x4006a8df0
        }
        val = {
          i = 0xbf21e0
        }
        internal_args = 0xbf2248
        count = 0xa0

In frame #11 make_gap_larger, current_buffer looks like:

(gdb) $1 = (struct buffer *) 0x9434730
(gdb) $2 = {
  header = {
    size = 0x4000000006032047
  },
  name_ = {
    i = 0x6b5d4b4
  },
  filename_ = {
    i = 0x0
  },
  directory_ = {
    i = 0x91406d4
  },
  backed_up_ = {
    i = 0x0
  },
  save_length_ = {
    i = 0x2
  },
  auto_save_file_name_ = {
    i = 0x0
  },
  read_only_ = {
    i = 0x0
  },
  mark_ = {
    i = 0x69ae731
  },
  local_var_alist_ = {
    i = 0x69526c3
  },
  major_mode_ = {
    i = 0x6938
  },
  mode_name_ = {
    i = 0x40032154c
  },
  mode_line_format_ = {
    i = 0x4007ff4a3
  },
  header_line_format_ = {
    i = 0x0
  },
  keymap_ = {
    i = 0x0
  },
  abbrev_table_ = {
    i = 0x4007c1855
  },
  syntax_table_ = {
    i = 0x400789e2d
  },
  category_table_ = {
    i = 0x40078a605
  },
  case_fold_search_ = {
    i = 0x0
  },
  tab_width_ = {
    i = 0x22
  },
  fill_column_ = {
    i = 0x13a
  },
  left_margin_ = {
    i = 0x2
  },
  auto_fill_function_ = {
    i = 0x0
  },
  downcase_table_ = {
    i = 0x40078ab5d
  },
  upcase_table_ = {
    i = 0x40078fbe5
  },
  case_canon_table_ = {
    i = 0x400985f35
  },
  case_eqv_table_ = {
    i = 0x400976965
  },
  truncate_lines_ = {
    i = 0xd510
  },
  word_wrap_ = {
    i = 0x0
  },
  ctl_arrow_ = {
    i = 0xd510
  },
  bidi_display_reordering_ = {
    i = 0xd510
  },
  bidi_paragraph_direction_ = {
    i = 0x0
  },
  selective_display_ = {
    i = 0x0
  },
  selective_display_ellipses_ = {
    i = 0xd510
  },
  minor_modes_ = {
    i = 0x0
  },
  overwrite_mode_ = {
    i = 0x0
  },
  abbrev_mode_ = {
    i = 0x0
  },
  display_table_ = {
    i = 0x0
  },
  mark_active_ = {
    i = 0x0
  },
  enable_multibyte_characters_ = {
    i = 0x0
  },
  buffer_file_coding_system_ = {
    i = 0xfffffffffec61568
  },
  file_format_ = {
    i = 0x0
  },
  auto_save_file_format_ = {
    i = 0xd510
  },
  cache_long_scans_ = {
    i = 0xd510
  },
  width_table_ = {
    i = 0x0
  },
  pt_marker_ = {
    i = 0x0
  },
  begv_marker_ = {
    i = 0x0
  },
  zv_marker_ = {
    i = 0x0
  },
  point_before_scroll_ = {
    i = 0x0
  },
  file_truename_ = {
    i = 0x0
  },
  invisibility_spec_ = {
    i = 0xd510
  },
  last_selected_window_ = {
    i = 0x0
  },
  display_count_ = {
    i = 0x2
  },
  left_margin_cols_ = {
    i = 0x2
  },
  right_margin_cols_ = {
    i = 0x2
  },
  left_fringe_width_ = {
    i = 0x0
  },
  right_fringe_width_ = {
    i = 0x0
  },
  fringes_outside_margins_ = {
    i = 0x0
  },
  scroll_bar_width_ = {
    i = 0x0
  },
  scroll_bar_height_ = {
    i = 0x0
  },
  vertical_scroll_bar_type_ = {
    i = 0xd510
  },
  horizontal_scroll_bar_type_ = {
    i = 0xd510
  },
  indicate_empty_lines_ = {
    i = 0xd510
  },
  indicate_buffer_boundaries_ = {
    i = 0x0
  },
  fringe_indicator_alist_ = {
    i = 0x400c28ab3
  },
  fringe_cursor_alist_ = {
    i = 0x40095d173
  },
  display_time_ = {
    i = 0x0
  },
  scroll_up_aggressively_ = {
    i = 0x0
  },
  scroll_down_aggressively_ = {
    i = 0x0
  },
  cursor_type_ = {
    i = 0xd510
  },
  extra_line_spacing_ = {
    i = 0x0
  },
  cursor_in_non_selected_windows_ = {
    i = 0xd510
  },
  own_text = {
    beg = 0x1f0000 "224 Overview information for 108895-109097 follows\r\n108895\tRe: Problem with whitespaces in search\ttomas@tuxteam.de\tThu, 28 Jan 2016 15:58:13 +0100\t<20160128145813.GB14779@tuxteam.de>\t<20160128101634.G"...,
    gpt = 0xf035,
    z = 0xf035,
    gpt_byte = 0xf035,
    z_byte = 0xf035,
    gap_size = 0x17d0,
    modiff = 0x45c,
    chars_modiff = 0x45c,
    save_modiff = 0x1,
    overlay_modiff = 0x1,
    compact = 0x1,
    beg_unchanged = 0x0,
    end_unchanged = 0x0,
    unchanged_modified = 0x1,
    overlay_unchanged_modified = 0x1,
    intervals = 0x0,
    markers = 0x69ae700,
    inhibit_shrinking = 0x0,
    redisplay = 0x1
  },
  text = 0x9434970,
  next = 0x9434ef0,
  pt = 0xf035,
  pt_byte = 0xf035,
  begv = 0x1,
  begv_byte = 0x1,
  zv = 0xf035,
  zv_byte = 0xf035,
  base_buffer = 0x0,
  indirections = 0x0,
  window_count = 0x0,
  local_flags = '\000' <repeats 49 times>,
  modtime = {
    tv_sec = 0x0,
    tv_nsec = 0xfffffffe
  },
  modtime_size = 0xffffffffffffffff,
  auto_save_modified = 0x0,
  display_error_modiff = 0x0,
  auto_save_failure_time = 0x0,
  last_window_start = 0x1,
  newline_cache = 0x4a222c0,
  width_run_cache = 0x0,
  bidi_paragraph_cache = 0x0,
  prevent_redisplay_optimizations_p = 0x1,
  clip_changed = 0x0,
  overlays_before = 0x0,
  overlays_after = 0x0,
  overlay_center = 0xf035,
  undo_list_ = {
    i = 0xd510
  }
}

...and in the same frame, current_buffer->text looks like this:

(gdb) $3 = (struct buffer_text *) 0x9434970
(gdb) $4 = {
  beg = 0x1f0000 "224 Overview information for 108895-109097 follows\r\n108895\tRe: Problem with whitespaces in search\ttomas@tuxteam.de\tThu, 28 Jan 2016 15:58:13 +0100\t<20160128145813.GB14779@tuxteam.de>\t<20160128101634.G"...,
  gpt = 0xf035,
  z = 0xf035,
  gpt_byte = 0xf035,
  z_byte = 0xf035,
  gap_size = 0x17d0,
  modiff = 0x45c,
  chars_modiff = 0x45c,
  save_modiff = 0x1,
  overlay_modiff = 0x1,
  compact = 0x1,
  beg_unchanged = 0x0,
  end_unchanged = 0x0,
  unchanged_modified = 0x1,
  overlay_unchanged_modified = 0x1,
  intervals = 0x0,
  markers = 0x69ae700,
  inhibit_shrinking = 0x0,
  redisplay = 0x1
}

Hopefully this is of some use.

    AndyM