Re: MPS: face-cache

[Eli Zaretskii <eliz@gnu.org>]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: Helmut Eller <eller.helmut@gmail.com>,  emacs-devel missing value
>  <emacs-devel@gnu.org>
> Date: Sun, 28 Apr 2024 07:06:45 +0200
> 
> Did that now, but it's still crashing. My impression, which might of
> course be completely wrong, is that we are losing faces somehow, i.e.
> something is wrong with the cache.

Could be.

But there's also FRAME_FONTSET, e.g. for w32:

  #define FRAME_FONTSET(f) ((f)->output_data.w32->fontset)

Are we handling it correctly vis-a-vis GC?  fix_frame doesn't do
anything with it, AFAICT.  Should it?

When Emacs is looking for a font, it consults the fontset.  In one
case, I got a crash with Helmut's recipe, like this:

  Thread 1 received signal SIGSEGV, Segmentation fault.
  parse_str_as_multibyte (
      str=0xc045000 <error: Cannot access memory at address 0xc045000>,
      str@entry=0xaa1a880 "", len=len@entry=211856320,
      nchars=nchars@entry=0x6df89cc, nbytes=nbytes@entry=0x6df89c8)
      at character.c:555
  555               int n = multibyte_length (str, NULL, false, false);
  (gdb) bt
  #0  parse_str_as_multibyte (
      str=0xc045000 <error: Cannot access memory at address 0xc045000>,
      str@entry=0xaa1a880 "", len=len@entry=211856320,
      nchars=nchars@entry=0x6df89cc, nbytes=nbytes@entry=0x6df89c8)
      at character.c:555
  #1  0x003141a1 in font_intern_prop (str=0xaa1a880 "", len=211856320,
      force_symbol=force_symbol@entry=true) at font.c:326
  #2  0x0031d387 in font_find_for_lface (f=f@entry=0xaa1c478,
      attrs=attrs@entry=0x1dc263b0, spec=0xcb8ebed, c=c@entry=21457)
      at lisp.h:751
  #3  0x003e7c01 in fontset_find_font (fontset=0xb41812d, c=c@entry=21457,
      face=face@entry=0x1dc263b0, charset_id=charset_id@entry=42,
      fallback=fallback@entry=false) at lisp.h:751
  #4  0x003e8475 in fontset_font (fontset=fontset@entry=0xb3fc765,
      c=c@entry=21457, face=face@entry=0x1dc263b0, id=42) at lisp.h:751
  #5  0x003e9232 in face_for_char (f=0xaa1c478, face=face@entry=0x1dc263b0,
      c=21457, pos=pos@entry=788, object=0x0) at fontset.c:1031
  #6  0x001a79d4 in FACE_FOR_CHAR (object=<optimized out>, pos=788,
      character=<optimized out>, face=0x1dc263b0, f=<optimized out>)
      at dispextern.h:1959
  #7  get_next_display_element (it=it@entry=0x6dfa6b0) at xdisp.c:8499
  #8  0x001b0d96 in display_line (it=it@entry=0x6dfa6b0,
      cursor_vpos=cursor_vpos@entry=1) at xdisp.c:25298
  #9  0x001b7611 in try_window (window=<optimized out>, window@entry=0xc8007b5,
      pos=..., flags=<optimized out>, flags@entry=1) at xdisp.c:21139
  #10 0x001d9947 in redisplay_window (window=window@entry=0xc8007b5,
      just_this_one_p=just_this_one_p@entry=false) at xdisp.c:20533
  #11 0x001dcb44 in redisplay_window_0 (window=0xc8007b5) at xdisp.c:18018
  #12 0x002f29db in internal_condition_case_1 (
      bfun=bfun@entry=0x1dcb0f <redisplay_window_0>, arg=arg@entry=0xc8007b5,
      handlers=0x1a3a10c3, hfun=hfun@entry=0x186297 <redisplay_window_error>)
      at eval.c:1568
  #13 0x00181eed in redisplay_windows (window=0xc8007b5) at xdisp.c:17987
  #14 0x001c0f5f in redisplay_internal () at xdisp.c:17387
  #15 0x001c24b3 in redisplay () at xdisp.c:16565
  #16 0x002661c8 in read_char (commandflag=<optimized out>, commandflag@entry=1,
      map=<optimized out>, map@entry=0xa820f7b, prev_event=<optimized out>,
      used_mouse_menu=<optimized out>, used_mouse_menu@entry=0x6dff7fb,
      end_time=<optimized out>, end_time@entry=0x0) at keyboard.c:2678
  #17 0x002697fd in read_key_sequence (keybuf=keybuf@entry=0x6dff8d8,
      prompt=prompt@entry=0x0,
      dont_downcase_last=dont_downcase_last@entry=false,
      can_return_switch_frame=<optimized out>,
      can_return_switch_frame@entry=true, fix_current_buffer=<optimized out>,
      fix_current_buffer@entry=true, prevent_redisplay=<optimized out>,
      prevent_redisplay@entry=false, disable_text_conversion_p=false)
      at keyboard.c:10727
  #18 0x0026b38b in command_loop_1 () at lisp.h:1179
  #19 0x002f293d in internal_condition_case (
      bfun=bfun@entry=0x26b1d0 <command_loop_1>, handlers=handlers@entry=0x48,
      hfun=hfun@entry=0x25e516 <cmd_error>) at eval.c:1544
  #20 0x0025482b in command_loop_2 (handlers=0x48) at keyboard.c:1168
  #21 0x002f2857 in internal_catch (tag=tag@entry=0x87a8,
      func=func@entry=0x25480b <command_loop_2>, arg=arg@entry=0x48)
      at eval.c:1224
  #22 0x002547cb in command_loop () at lisp.h:1179
  #23 0x0025e0d1 in recursive_edit_1 () at keyboard.c:754
  #24 0x0025e3c1 in Frecursive_edit () at keyboard.c:837
  #25 0x00497d5f in main (argc=<optimized out>, argv=<optimized out>)
      at emacs.c:2626

Note that the string length in parse_str_as_multibyte is completely
bogus, which led me look into what we do with fontsets, because frame
#4 calls fontset_font.  The default fontset, Vdefault_fontset, is
staticpro'd, but that's all I found.