FvwmIconMan segfault in FlocaleEncodeString from setup_icon_title_size

[OsmiumBalloon]

SUMMARY

FVWM 3 1.1.4 segfaulted upon clicking in FvwmIconMan to switch windows. Faulted in FlocaleEncodeString called from setup_icon_title_size.

ENVIRONMENT

• FVWM 3 version 1.1.4-15-g3abfb28 (built from git checkout)
• Debian 12.14 "bookworm"
• Kernel 6.12.9+bpo-amd64 / 6.12.9-1~bpo12+1 (2025-01-19)
• GCC 12.2.0 (12.2.0-14+deb12u1)
• X.Org 1.21.1.7 (2:21.1.7-3+deb12u12)
• Lenovo ThinkPad T16 Gen3
• Intel Core Ultra 7 155U CPU
• Intel "Meteor Lake-P" graphics, HWID 8086:7D45

BACKGROUND

I normally boot to text console, login, and do "startx". My .xinitrc starts FVWM and uses that as the session controller for X. When FVWM exits, so does X.

This X+FVWM session had been started about 2 weeks ago.

I have FvwmIconMan set-up to show windows on the current desktop, sort-of like the Microsoft Windows task bar, except in a stack along the left (not a strip along the bottom). FvwmIconMan is swallowed by FvwmDock, which is also set-up to be along the left edge of the screen (vaguely like a NeXTstep Dock).

PROBLEM

I was working in some window, likely a Firefox window. I needed to switch to another window, that one definitely a Firefox window. I am pretty sure (but not 100%) the desired window was not iconified, merely obscured behind other windows. I clicked the button for the desired window in FvwmIconMan. FVWM crashed. X exited, and I found myself sitting at the text console shell prompt.

Logs immediately revealed FVWM crashed with a segmentation fault. I restarted my X session and it has been working OK for a few hours now. I collected debugging assets.

I suspect I have hit this crash before, but this is the first time it has happened on recent code and with a successful core capture.

EXTRACTS

Exit detail from my .xinitrc:

2026-06-02 16:34:04 FVWM exit status=139

Log entry from minicoredumper:

fvwm3[2610]: segfault at 58 ip 0000561680641820 sp 00007fffc6b55b10 error 4 in fvwm3[cc820,561680585000+e3000] likely on CPU 7 (core 3, socket 0)
Code: 00 00 48 83 7d 10 00 74 0a 48 8b 45 10 c7 00 00 00 00 00 48 8b 45 a0 c7 00 00 00 00 00 48 8b 45 90 8b 55 9c 89 10 48 8b 45 b0 <48> 8b 40 58 48 85 c0 74 22 48 8b 45 b0 48 8b 40 50 48 85 c0 74 15

Backtrace from GDB:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000561680641820 in FlocaleEncodeString (dpy=0x561682ca4230, flf=0x0, str=0x561682e156c0 "", do_free=0x7fffc6b55be0, len=50, nl=0x7fffc6b55be4, is_rtl=0x0, comb_chars=0x7fffc6b55bd8, l_to_v=0x0) at ../libs/Flocale.c:446
446		if (flf->str_fc == NULL || flf->fc == NULL ||

Thread 1 (Thread 0x7f749be95340 (LWP 2610)):
#0  0x0000561680641820 in FlocaleEncodeString (dpy=0x561682ca4230, flf=0x0, str=0x561682e156c0 "", do_free=0x7fffc6b55be0, len=50, nl=0x7fffc6b55be4, is_rtl=0x0, comb_chars=0x7fffc6b55bd8, l_to_v=0x0) at ../libs/Flocale.c:446
#1  0x0000561680645f57 in FlocaleTextWidth (flf=0x0, str=0x561682e156c0 "", sl=50) at ../libs/Flocale.c:2186
#2  0x00005616805db879 in setup_icon_title_size (fw=0x561682cd3d50) at ../fvwm/icons.c:143
#3  0x00005616805dc88c in CreateIconWindow (fw=0x561682cd3d50, def_x=3920, def_y=1548) at ../fvwm/icons.c:592
#4  0x00005616805e1df0 in Iconify (fw=0x561682cd3d50, win_opts=0x7fffc6b55e60) at ../fvwm/icons.c:2550
#5  0x00005616805e232a in CMD_Iconify (cond_rc=0x7fffc6b55f28, exc=0x561682ce52c0, action=0x561682e2c947 "", pc=0x7fffc6b55f30) at ../fvwm/icons.c:2695
#6  0x00005616805d0995 in _execute_command_line (cond_rc=0x0, exc=0x561682ee9ea0, xaction=0x561682ed3988 "", caller_pc=0x0, exec_flags=256, all_pos_args_string=0x0, pos_arg_tokens=0x0, has_ref_window_moved=0) at ../fvwm/functions.c:673
#7  0x00005616805d19ca in execute_function (cond_rc=0x0, exc=0x561682ee9ea0, action=0x561682ed3988 "", pc=0x0, exec_flags=256) at ../fvwm/functions.c:1241
#8  0x00005616805fd3b3 in module_input_execute (input=0x561682ed3970) at ../fvwm/module_interface.c:768
#9  0x00005616805fd446 in ExecuteCommandQueue () at ../fvwm/module_interface.c:807
#10 0x00005616805bb4ef in My_XNextEvent (disp=0x561682ca4230, event=0x7fffc6b56350) at ../fvwm/events.c:4397
#11 0x00005616805bb00d in HandleEvents () at ../fvwm/events.c:4225
#12 0x00005616805d7dbc in main (argc=2, argv=0x7fffc6b56808) at ../fvwm/fvwm3.c:2391

AVAILABLE ARTIFACTS

• Partial core dump (produced by minicoredumper)
• Log files from the crash
  • fvwm3-output.log
  • Xorg.0.log
  • xclients.out
  • log from minicoredumper
• Output of various commands
  • fvwm -V
  • gdb -c fvwm.core fvmw3
    • info registers
    • info threads
    • thread apply all bt
    • thread apply all bt full
    • x/16i $pc
• Copy of my FVWM config files
• Copy of installed FVWM binaries
• Copy of source tree used to build said binaries

Core, logs, output, and config attached. Binaries and/or build tree available upon request.

• fvwm3-V.out.txt
• fvwm.core.gz
• logs.tar.gz
• gdb.tar.gz
• fvwmconf.tar.gz

Please let me know if there is anything more I can do or provide.