Segmentation Fault in Footclient

[quantumfate]

I use chafa and footclient to have a neat "alt+tab" window with a preview of the selected window. However, it took me a while to realize that chafa segfaults on footclient specifically. The preview of images works fine in Kitty for example and used to work upon 2 months ago in foot as well.

11:35 quantum ~ chafa --animate false --dither=none $XDG_RUNTIME_DIR/hypr/alttab/preview.png 
[1]    792587 segmentation fault (core dumped)  chafa --animate false --dither=none $XDG_RUNTIME_DIR/hypr/alttab/preview.png

Output of chafa --version:

Chafa version 1.18.2

Loaders:  AVIF GIF HEIF JPEG JXL PNG QOI SVG TIFF WebP XWD
Features: mmx sse4.1 popcnt avx2
Applying: mmx sse4.1 popcnt avx2

Copyright (C) 2018-2025 Hans Petter Jansson et al.
Incl. libnsgif copyright (C) 2004 Richard Wilson, copyright (C) 2008 Sean Fox
Incl. LodePNG copyright (C) 2005-2018 Lode Vandevenne
Incl. QOI decoder copyright (C) 2021 Dominic Szablewski

This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

If you need more info for diagnosis please let me know, thank you!

[hpjansson]

Thanks for reporting this! I do need a bit more information:

• Is this on an AMD CPU? I think it's more sensitive to misaligned AVX addressing.

• Can you install debuginfo for chafa and glib, and reproduce the crash under gdb? It should be as simple as:

gdb chafa
(gdb) run image.png
...crash...
(gdb) t a a bt

The resulting trace should be useful.

If you could attach an image that makes it crash, that would also be useful.

[quantumfate]

Hey, thank you for your effort on this project!

Your guess was right about the AMD CPU and I will give you my output of `lscpu` for my current system:

Architecture:                x86_64
  CPU op-mode(s):            32-bit, 64-bit
  Address sizes:             48 bits physical, 48 bits virtual
  Byte Order:                Little Endian
CPU(s):                      16
  On-line CPU(s) list:       0-15
Vendor ID:                   AuthenticAMD
  Model name:                AMD Ryzen 7 7800X3D 8-Core Processor
    CPU family:              25
    Model:                   97
    Thread(s) per core:      2
    Core(s) per socket:      8
    Socket(s):               1
    Stepping:                2
    Microcode version:       0xa60120c
    Frequency boost:         disabled
    CPU(s) scaling MHz:      77%
    CPU max MHz:             5053,3770
    CPU min MHz:             426,1890
    BogoMIPS:                8399,98
    Flags:                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm con
                             stant_tsc rep_good amd_lbr_v2 nopl xtopology nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe p
                             opcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr
                             _core perfctr_nb bpext perfctr_llc mwaitx cpuid_fault cat_l3 cdp_l3 hw_pstate ssbd mba perfmon_v2 ibrs ibpb stibp ibrs_enhanced vmmcall fsgsbase bmi1
                              avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec 
                             xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local user_shstk avx512_bf16 clzero irperf xsaveerptr rdpru wbnoinvd cppc arat npt lbrv sv
                             m_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic vgif x2avic v_spec_ctrl vnmi avx512vbmi umip pku ospke a
                             vx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg avx512_vpopcntdq rdpid overflow_recov succor smca fsrm flush_l1d amd_lbr_pmc_freeze
Virtualization features:     
  Virtualization:            AMD-V
Caches (sum of all):         
  L1d:                       256 KiB (8 instances)
  L1i:                       256 KiB (8 instances)
  L2:                        8 MiB (8 instances)
  L3:                        96 MiB (1 instance)
NUMA:                        
  NUMA node(s):              1
  NUMA node0 CPU(s):         0-15
Vulnerabilities:             
  Gather data sampling:      Not affected
  Ghostwrite:                Not affected
  Indirect target selection: Not affected
  Itlb multihit:             Not affected
  L1tf:                      Not affected
  Mds:                       Not affected
  Meltdown:                  Not affected
  Mmio stale data:           Not affected
  Old microcode:             Not affected
  Reg file data sampling:    Not affected
  Retbleed:                  Not affected
  Spec rstack overflow:      Mitigation; Safe RET
  Spec store bypass:         Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:                Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Spectre v2:                Mitigation; Enhanced / Automatic IBRS; IBPB conditional; STIBP always-on; PBRSB-eIBRS Not affected; BHI Not affected
  Srbds:                     Not affected
  Tsa:                       Mitigation; Clear CPU buffers
  Tsx async abort:           Not affected
  Vmscape:                   Mitigation; IBPB before exit to userspace

As requested here is the output of GDB with the crash reproduced:

(gdb) run /run/user/1000/hypr/alttab/preview.png 
Starting program: /usr/bin/chafa /run/user/1000/hypr/alttab/preview.png
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7fffef7ff6c0 (LWP 2423837)]
[New Thread 0x7fffeeffe6c0 (LWP 2423838)]
[New Thread 0x7fffee7fd6c0 (LWP 2423839)]
[New Thread 0x7fffedffc6c0 (LWP 2423840)]

Thread 1 "chafa" received signal SIGSEGV, Segmentation fault.
Downloading 133.09 K source file /usr/src/debug/chafa/chafa/chafa/internal/smolscale/smolscale-avx2.c
0x00007ffff6db8b85 in repack_row_1234_64_PREMUL8_COMPRESSED_to_4132_32_PREMUL8_COMPRESSED () at internal/smolscale/smolscale-avx2.c:1010                                          
1010	DEF_REPACK_FROM_1234_64BPP_TO_32BPP (4, 1, 3, 2)
(gdb) t a a bt

Thread 5 (Thread 0x7fffedffc6c0 (LWP 2423840) "pool-0"):
#0  0x00007ffff6947f8d in syscall () from /usr/lib/libc.so.6
#1  0x00007ffff6c6f774 in g_cond_wait_until_impl (cond=<optimized out>, mutex=0x5555555bf580, end_time=<optimized out>) at ../glib/glib/gthread-posix.c:1159
#2  g_cond_wait_until (cond=<optimized out>, mutex=0x5555555bf580, end_time=<optimized out>) at ../glib/glib/gthread.c:1782
#3  0x00007ffff6bee610 in g_async_queue_pop_intern_unlocked (queue=0x5555555bf580, wait=1, end_time=<optimized out>) at ../glib/glib/gasyncqueue.c:379
#4  g_async_queue_timeout_pop_unlocked (queue=0x5555555bf580, timeout=<optimized out>) at ../glib/glib/gasyncqueue.c:531
#5  0x00007ffff6c7800b in g_thread_pool_wait_for_new_task (pool=0x5555555bfdd0) at ../glib/glib/gthreadpool.c:262
#6  g_thread_pool_thread_proxy (data=<optimized out>) at ../glib/glib/gthreadpool.c:325
#7  0x00007ffff6c775e3 in g_thread_proxy (data=0x7fffe0000b80) at ../glib/glib/gthread.c:893
#8  0x00007ffff68ace31 in ?? () from /usr/lib/libc.so.6
#9  0x00007ffff694abdc in ?? () from /usr/lib/libc.so.6

Thread 4 (Thread 0x7fffee7fd6c0 (LWP 2423839) "pool-spawner"):
#0  0x00007ffff6947f8d in syscall () from /usr/lib/libc.so.6
#1  0x00007ffff6c6eae5 in g_cond_wait_impl (cond=0x5555555bf618, mutex=0x5555555bf610) at ../glib/glib/gthread-posix.c:1026
#2  g_cond_wait (cond=0x5555555bf618, mutex=0x5555555bf610) at ../glib/glib/gthread.c:1686
#3  0x00007ffff6bee40d in g_async_queue_pop_intern_unlocked (end_time=-1, queue=0x5555555bf610, wait=1) at ../glib/glib/gasyncqueue.c:376
#4  g_async_queue_pop_unlocked (queue=0x5555555bf610) at ../glib/glib/gasyncqueue.c:432
#5  0x00007ffff6c77b29 in g_thread_pool_spawn_thread (data=<optimized out>) at ../glib/glib/gthreadpool.c:297
#6  0x00007ffff6c775e3 in g_thread_proxy (data=0x5555555bf6a0) at ../glib/glib/gthread.c:893
#7  0x00007ffff68ace31 in ?? () from /usr/lib/libc.so.6
#8  0x00007ffff694abdc in ?? () from /usr/lib/libc.so.6

Thread 3 (Thread 0x7fffeeffe6c0 (LWP 2423838) "stream-reader"):
#0  0x00007ffff68b6072 in ?? () from /usr/lib/libc.so.6
#1  0x00007ffff68a90cf in ?? () from /usr/lib/libc.so.6
#2  0x00007ffff693b9ea in poll () from /usr/lib/libc.so.6
#3  0x000055555555d652 in read_from_stream () at /usr/src/debug/chafa/chafa/tools/chafa/chafa-stream-reader.c:148
#4  thread_main () at /usr/src/debug/chafa/chafa/tools/chafa/chafa-stream-reader.c:251
#5  0x00007ffff6c775e3 in g_thread_proxy (data=0x555555602810) at ../glib/glib/gthread.c:893
#6  0x00007ffff68ace31 in ?? () from /usr/lib/libc.so.6
#7  0x00007ffff694abdc in ?? () from /usr/lib/libc.so.6

Thread 2 (Thread 0x7fffef7ff6c0 (LWP 2423837) "stream-writer"):
#0  0x00007ffff6947f8d in syscall () from /usr/lib/libc.so.6
#1  0x00007ffff6c6eae5 in g_cond_wait_impl (cond=0x555555601800, mutex=0x5555556017f8) at ../glib/glib/gthread-posix.c:1026
#2  g_cond_wait (cond=0x555555601800, mutex=0x5555556017f8) at ../glib/glib/gthread.c:1686
#3  0x000055555555d8b7 in thread_main () at /usr/src/debug/chafa/chafa/tools/chafa/chafa-stream-writer.c:319
#4  0x00007ffff6c775e3 in g_thread_proxy (data=0x555555601990) at ../glib/glib/gthread.c:893
#5  0x00007ffff68ace31 in ?? () from /usr/lib/libc.so.6
#6  0x00007ffff694abdc in ?? () from /usr/lib/libc.so.6

Thread 1 (Thread 0x7ffff3fb7d40 (LWP 2423727) "chafa"):
#0  0x00007ffff6db8b85 in repack_row_1234_64_PREMUL8_COMPRESSED_to_4132_32_PREMUL8_COMPRESSED () at internal/smolscale/smolscale-avx2.c:1010
#1  0x00007ffff6dccc11 in populate_clear_batch () at internal/smolscale/smolscale.c:885
#2  get_implementations () at internal/smolscale/smolscale.c:1037
#3  smol_scale_init () at internal/smolscale/smolscale.c:1229
#4  smol_scale_new_full.constprop.0 () at internal/smolscale/smolscale.c:1358
#5  0x00007ffff6d7ff17 in chafa_indexed_image_draw_pixels () at internal/chafa-indexed-image.c:502
#6  0x00007ffff6d61005 in chafa_sixel_canvas_draw_all_pixels () at internal/chafa-sixel-canvas.c:103
#7  chafa_sixel_canvas_draw_all_pixels () at internal/chafa-sixel-canvas.c:87
#8  draw_all_pixels () at /usr/src/debug/chafa/chafa/chafa/chafa-canvas.c:1356
#9  0x0000555555563f37 in build_canvas () at /usr/src/debug/chafa/chafa/tools/chafa/chafa.c:597
#10 run_generic () at /usr/src/debug/chafa/chafa/tools/chafa/chafa.c:792
--Type <RET> for more, q to quit, c to continue without paging--c
#11 0x000055555555be8c in run_vertical () at /usr/src/debug/chafa/chafa/tools/chafa/chafa.c:953
#12 main () at /usr/src/debug/chafa/chafa/tools/chafa/chafa.c:1074

Please don't hesitate to reach out in the future for testing purposes, I use chafa very frequently :)

[hpjansson]

Great! I've committed a changeset to the master branch that I think will fix this. Want to build a checkout and test?

[quantumfate]

Hey thank you for the fix! I've just built on master and tested it - seems to be working now!

➜ 11:31 quantum chafa (master) ✔ ./chafa --version
Chafa version 1.19.0

Loaders:  AVIF GIF HEIF JPEG JXL PNG QOI SVG TIFF WebP XWD
Features: mmx sse4.1 popcnt avx2
Applying: mmx sse4.1 popcnt avx2

Copyright (C) 2018-2025 Hans Petter Jansson et al.
Incl. libnsgif copyright (C) 2004 Richard Wilson, copyright (C) 2008 Sean Fox
Incl. LodePNG copyright (C) 2005-2018 Lode Vandevenne
Incl. QOI decoder copyright (C) 2021 Dominic Szablewski

This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.