Emacs Crashes When Opening Certain Buffers

[ghost]

System: Arch Linux
Emacs Version: 27.0.50

Using the popular Doom-Emacs, opening certain buffers immediately causes emacs to crash. For instance, when in Zoom-Mode and opening neotree Emacs stops responding and is subsequently killed.

[cyrus-and]

I can confirm that, the backtrace looks like this for GNU Emacs 26.0.90 on Debian:

Fatal error 11: Segmentation fault
Backtrace:
emacs[0x50b635]
emacs[0x4f1b54]
emacs[0x509d9e]
emacs[0x50a089]
emacs[0x50a0c0]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x110c0)[0x7faf647780c0]
emacs[0x432487]
emacs[0x455ea4]
emacs[0x4fbd0b]
emacs[0x4fe8e7]
emacs[0x500434]
emacs[0x565bde]
emacs[0x4f1ee4]
emacs[0x565b7c]
emacs[0x4f1ea0]
emacs[0x4f6743]
emacs[0x4f6ab3]
emacs[0x419dd4]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7faf63b412e1]
emacs[0x41ab0a]
Segmentation fault

Anyway even though Zoom is involved in this, this is surely a bug in Emacs itself at this stage, it shouldn't be possible to cause a segmentation fault from an elisp program. I suggest to file an issue to Emacs, M-x report-emacs-bug seems the right tool for the job or use the mailing list.

Feel free to link this issue in the description and to add any further information here.

[cyrus-and]

Using GDB:

[0] from 0x0000000000432487 in reconsider_clip_changes+23 at xdisp.c:13699
[1] from 0x0000000000455ea4 in redisplay_internal+708 at xdisp.c:13909
[2] from 0x0000000000458185 in redisplay+5 at xdisp.c:13488
[3] from 0x00000000004fbd0b in read_char+2155 at keyboard.c:2480
[4] from 0x00000000004fe8e7 in read_key_sequence+951 at keyboard.c:9147
[5] from 0x0000000000500434 in command_loop_1+548 at keyboard.c:1368
[6] from 0x0000000000565bde in internal_condition_case+62 at eval.c:1332
[7] from 0x00000000004f1ee4 in command_loop_2+36 at keyboard.c:1110
[8] from 0x0000000000565b7c in internal_catch+92 at eval.c:1097
[9] from 0x00000000004f1ea0 in command_loop+160 at keyboard.c:1089
[10] from 0x00000000004f6743 in recursive_edit_1+115 at keyboard.c:695
[11] from 0x00000000004f6ab3 in Frecursive_edit+227 at keyboard.c:766
[12] from 0x0000000000419dd4 in main+2740 at emacs.c:1713

The segmentation fault happens here:

static void
reconsider_clip_changes (struct window *w)
{
  struct buffer *b = XBUFFER (w->contents);

  if (b->clip_changed // *** SEGMENTATION FAULT ***
      && w->window_end_valid
      && w->current_matrix->buffer == b
      && w->current_matrix->zv == BUF_ZV (b)
      && w->current_matrix->begv == BUF_BEGV (b))
    b->clip_changed = false;

  /* If display wasn't paused, and W is not a tool bar window, see if
     point has been moved into or out of a composition.  In that case,
     set b->clip_changed to force updating the screen.  If
     b->clip_changed has already been set, skip this check.  */
  if (!b->clip_changed && w->window_end_valid)
    {
      ptrdiff_t pt = (w == XWINDOW (selected_window)
                      ? PT : marker_position (w->pointm));

      if ((w->current_matrix->buffer != b || pt != w->last_point)
          && check_point_in_composition (w->current_matrix->buffer,
                                         w->last_point, b, pt))
        b->clip_changed = true;
    }
}

[cyrus-and]

Steps to reproduce this are:

1. start with a fresh doom-emacs setup;
2. M-x load-file RET /path/to/zoom.el;
3. M-x zoom-mode;
4. M-x neotree-show.

Note: it does not happen with only NeoTree and Zoom.

Someone should narrow it down and submit a proper bug report.

[cyrus-and]

FWIW here is the "bug report".