Package: emacs;
Reported by: Yifan Zhu <fanzhuyifan <at> gmail.com>
Date: Mon, 17 Mar 2025 07:54:03 UTC
Severity: normal
Found in version 31.0.50
Done: Eli Zaretskii <eliz <at> gnu.org>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Yifan Zhu <fanzhuyifan <at> gmail.com> To: Eli Zaretskii <eliz <at> gnu.org> Cc: 77065 <at> debbugs.gnu.org Subject: bug#77065: 31.0.50; Infinite loop in move_it_to Date: Mon, 17 Mar 2025 19:36:15 -0700
On 3/17/25 7:27 AM, Eli Zaretskii wrote:
> Thanks, but I don't have access to a system where these prerequisites
> can be met. So either someone can reproduce this, debug the problem,
> and describe the reason for the loop, or I'd need to ask you to do it,
> if possible. Or, if you can show a recipe for reproducing the problem
> without installing LaTeX and xenops, I could try reproducing this on
> the systems to which I have access.
Right now I have a conjecture about what might be causing the infinite
loop -- when line number are produced, we can no longer use it->hpos ==
0 to test if the glyph is the first glyph. Perhaps this is best
explained by the following diff:
diff --git a/src/xdisp.c b/src/xdisp.c
index d7e0691c44d..0f4210ab814 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9972,6 +9972,7 @@ move_it_in_display_line_to (struct it *it,
ptrdiff_t prev_pos = IT_CHARPOS (*it);
bool saw_smaller_pos = prev_pos < to_charpos;
bool line_number_pending = false;
+ int initial_hpos = 0;
int this_line_subject_to_line_prefix = 0;
#ifdef GLYPH_DEBUG
@@ -10037,7 +10038,10 @@ #define BUFFER_POS_REACHED_P() \
&& should_produce_line_number (it))
{
if (it->current_x == it->first_visible_x)
- maybe_produce_line_number (it);
+ {
+ maybe_produce_line_number (it);
+ initial_hpos = it->hpos;
+ }
else
line_number_pending = true;
}
@@ -10298,7 +10302,7 @@ #define IT_RESET_X_ASCENT_DESCENT(IT) \
if (/* IT->hpos == 0 means the very first glyph
doesn't fit on the line, e.g. a wide
image. */
- it->hpos == 0
+ it->hpos == initial_hpos
|| (new_x == it->last_visible_x
&& FRAME_WINDOW_P (it->f)))
{
@@ -10474,6 +10478,7 @@ #define IT_RESET_X_ASCENT_DESCENT(IT) \
line_number_pending = false;
it->current_x = it->first_visible_x;
maybe_produce_line_number (it);
+ initial_hpos = it->hpos;
it->current_x += new_x - it->first_visible_x;
}
/* Glyph is visible. Increment number of glyphs that
Some other evidence includes the following gdb session:
(TLDR: in `move_it_in_display_line_to`, maybe_produce_line_number
increases it->hpos from 0 to 4. Thus afterwards the test for the glyph
being the first one fails)
(gdb) r ~/Downloads/main.tex
+r ~/Downloads/main.tex
Starting program: /home/yifan/packages/emacs-git/build/bin/emacs
~/Downloads/main.tex
^Z
Thread 1 "emacs" received signal SIGTSTP, Stopped (user).
(gdb) bt
#0 0x00005555556f54c5 in EQ (x=0x5555570825c4, y=0x5555570825c4) at
/home/yifan/packages/emacs-git/src/lisp.h:1327
#1 0x00005555557002e8 in face_attr_equal_p (v1=0x5555570825c4,
v2=0x5555570825c4) at xfaces.c:4417
#2 0x0000555555700416 in lface_equal_p (v1=0x5555588380d0,
v2=0x7ffffffecc80) at xfaces.c:4450
#3 0x000055555570157d in lookup_face (f=0x555555ecda90,
attr=0x7ffffffecc80) at xfaces.c:5012
#4 0x00005555557018c0 in lookup_named_face (w=0x555555ecdce8,
f=0x555555ecda90, symbol=0x67e0, signal_p=false) at xfaces.c:5099
#5 0x0000555555701bd4 in lookup_basic_face (w=0x555555ecdce8,
f=0x555555ecda90, face_id=0) at xfaces.c:5163
#6 0x0000555555664ed2 in produce_special_glyphs (it=0x7ffffffee420,
what=IT_CONTINUATION) at xdisp.c:32433
#7 0x000055555560d7e8 in init_iterator (it=0x7ffffffee420,
w=0x555555ecdce8, charpos=-1, bytepos=-1, row=0x5555559f8ba0
<scratch_glyph_row>, base_face_id=DEFAULT_FACE_ID) at xdisp.c:3365
#8 0x000055555564ce8d in maybe_produce_line_number (it=0x7fffffff6e20)
at xdisp.c:25201
#9 0x000055555561f53e in move_it_in_display_line_to (it=0x7fffffff6e20,
to_charpos=307, to_x=-1, op=MOVE_TO_POS) at xdisp.c:10040
#10 0x0000555555622e6c in move_it_to (it=0x7fffffff6e20, to_charpos=307,
to_x=-1, to_y=-1, to_vpos=-1, op=8) at xdisp.c:10945
#11 0x0000555555623a79 in move_it_vertically_backward
(it=0x7fffffff9700, dy=448) at xdisp.c:11159
#12 0x000055555563e600 in redisplay_window (window=0x555555ecdced,
just_this_one_p=false) at xdisp.c:20925
#13 0x00005555556349fd in redisplay_window_0 (window=0x555555ecdced) at
xdisp.c:18230
#14 0x00005555557f1e3e in internal_condition_case_1 (bfun=0x5555556349bb
<redisplay_window_0>, arg=0x555555ecdced, handlers=0x7fffef32b4b3,
hfun=0x555555634899 <redisplay_window_error>) at eval.c:1644
#15 0x000055555563486f in redisplay_windows (window=0x555555ecdced) at
xdisp.c:18199
#16 0x000055555563481e in redisplay_windows (window=0x5555587c5bcd) at
xdisp.c:18193
#17 0x0000555555633616 in redisplay_internal () at xdisp.c:17616
#18 0x00005555556315c3 in redisplay () at xdisp.c:16772
#19 0x000055555572b711 in read_char (commandflag=1, map=0x55555851b4e3,
prev_event=0x0, used_mouse_menu=0x7fffffffd73a, end_time=0x0) at
keyboard.c:2672
#20 0x000055555573e443 in read_key_sequence (keybuf=0x7fffffffd9b0,
prompt=0x0, dont_downcase_last=false, can_return_switch_frame=true,
fix_current_buffer=true, prevent_redisplay=false,
disable_text_conversion_p=false) at keyboard.c:10757
#21 0x0000555555727d97 in command_loop_1 () at keyboard.c:1424
#22 0x00005555557f1d97 in internal_condition_case (bfun=0x555555727989
<command_loop_1>, handlers=0x90, hfun=0x555555726eba <cmd_error>) at
eval.c:1620
#23 0x00005555557275d6 in command_loop_2 (handlers=0x90) at keyboard.c:1163
#24 0x00005555557f12ec in internal_catch (tag=0x11f10,
func=0x5555557275ac <command_loop_2>, arg=0x90) at eval.c:1300
#25 0x0000555555727568 in command_loop () at keyboard.c:1141
#26 0x0000555555726a5c in recursive_edit_1 () at keyboard.c:749
#27 0x0000555555726c08 in Frecursive_edit () at keyboard.c:832
#28 0x0000555555722cc5 in main (argc=2, argv=0x7fffffffde98) at emacs.c:2560
(gdb) break move_it_in_display_line_to
+break move_it_in_display_line_to
Breakpoint 2 at 0x55555561f329: file xdisp.c, line 9963.
(gdb) c
+c
Continuing.
Thread 1 "emacs" hit Breakpoint 2, move_it_in_display_line_to
(it=0x7fffffff6e20, to_charpos=307, to_x=-1, op=MOVE_TO_POS) at xdisp.c:9963
9963 {
(gdb) watch it->hpos
+watch it->hpos
Hardware watchpoint 3: it->hpos
(gdb) p it->hpos
+p it->hpos
$1 = 0
(gdb) c
+c
Continuing.
Thread 1 "emacs" hit Hardware watchpoint 3: it->hpos
Old value = 0
New value = 1
maybe_produce_line_number (it=0x7fffffff6e20) at xdisp.c:25292
25292 if (p)
(gdb)
+c
Continuing.
Thread 1 "emacs" hit Hardware watchpoint 3: it->hpos
Old value = 1
New value = 2
maybe_produce_line_number (it=0x7fffffff6e20) at xdisp.c:25292
25292 if (p)
(gdb)
+c
Continuing.
Thread 1 "emacs" hit Hardware watchpoint 3: it->hpos
Old value = 2
New value = 3
maybe_produce_line_number (it=0x7fffffff6e20) at xdisp.c:25292
25292 if (p)
(gdb)
+c
Continuing.
Thread 1 "emacs" hit Hardware watchpoint 3: it->hpos
Old value = 3
New value = 4
maybe_produce_line_number (it=0x7fffffff6e20) at xdisp.c:25292
25292 if (p)
(gdb) fini
+fini
Run till exit from #0 maybe_produce_line_number (it=0x7fffffff6e20) at
xdisp.c:25292
0x000055555561f53e in move_it_in_display_line_to (it=0x7fffffff6e20,
to_charpos=307, to_x=-1, op=MOVE_TO_POS) at xdisp.c:10040
10040 maybe_produce_line_number (it);
(gdb) next
+next
10045 if (it->area == TEXT_AREA && !it->string_from_prefix_prop_p)
(gdb)
+next
10046 handle_line_prefix (it);
(gdb)
+next
10051 this_line_subject_to_line_prefix =
it->string_from_prefix_prop_p;
(gdb)
+next
10054 if (IT_CHARPOS (*it) < CHARPOS (this_line_min_pos))
(gdb)
+next
10059 int x, i, ascent = 0, descent = 0;
(gdb)
+next
10068 if ((op & MOVE_TO_POS) != 0
(gdb)
+next
10069 && BUFFERP (it->object)
(gdb)
+next
10070 && it->method == GET_FROM_BUFFER
(gdb)
+next
10110 if (!get_next_display_element (it))
(gdb)
+next
10116 if (it->line_wrap == TRUNCATE)
(gdb)
+next
10135 if (it->line_wrap == WORD_WRAP && it->area == TEXT_AREA)
(gdb)
+next
10137 bool next_may_wrap = may_wrap;
(gdb)
+next
10139 if (char_can_wrap_after (it))
(gdb)
+next
10140 next_may_wrap = true;
(gdb)
+next
10144 if (may_wrap && char_can_wrap_before (it))
(gdb)
+next
10170 may_wrap = next_may_wrap;
(gdb)
+next
10176 ascent = it->max_ascent;
(gdb)
+next
10177 descent = it->max_descent;
(gdb)
+next
10183 x = it->current_x;
(gdb)
+next
10185 PRODUCE_GLYPHS (it);
(gdb)
+next
10187 if (it->area != TEXT_AREA)
(gdb)
+next
10222 if (it->nglyphs)
(gdb)
+next
10226 int single_glyph_width = it->pixel_width / it->nglyphs;
(gdb)
+next
10228 int x_before_this_char = x;
(gdb)
+next
10229 int hpos_before_this_char = it->hpos;
(gdb)
+next
10231 for (i = 0; i < it->nglyphs; ++i, x = new_x)
(gdb)
+next
10233 new_x = x + single_glyph_width;
(gdb)
+next
10236 if ((op & MOVE_TO_X) && new_x > to_x)
(gdb)
+next
10271 it->line_wrap != TRUNCATE
(gdb)
+next
10270 if (/* Lines are continued. */
(gdb)
+next
10273 new_x > it->last_visible_x
(gdb)
+next
10272 && (/* And glyph doesn't fit on the line. */
(gdb)
+next
10284 && (!this_line_subject_to_line_prefix
(gdb)
+next
10296 bool moved_forward = false;
(gdb)
+next
10301 it->hpos == 0
(gdb)
+next
10298 if (/* IT->hpos == 0 means the very first glyph
(gdb)
+next
10302 || (new_x == it->last_visible_x
(gdb)
+next
10414 IT_RESET_X_ASCENT_DESCENT (it);
(gdb) quit
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