Open nihathrael opened 5 years ago
CatxFish
commented
5 years ago I have some hardware problem on my Linux machine , I'll check it later. The previous output seems not stop properly, there might be some issue there.
update: Can't reproduce on Ubuntu , try to do more digging.
darkmattercoder
commented
4 years ago Same for me here on arch linux.
However I have no debugging symbols atm.
info: Output 'V4l2sink': stopping
info: Output 'V4l2sink': Total frames output: 56
info: Output 'V4l2sink': Total drawn frames: 57
[New Thread 0x7fff870a1700 (LWP 43932)]
[Thread 0x7fff870a1700 (LWP 43932) exited]
Thread 1 "obs" received signal SIGSEGV, Segmentation fault.
0x00007ffff4db9460 in free () from /usr/lib/libc.so.6
kautsig
commented
4 years ago I was also affected by this, it occurred when using the AUR package. At the time of writing it is marked as outdated, see [1]
To rule out an issue with the AUR package, I built obs-v4l2sink manually from source and installed it in my home directory (OBS and obs-v4l2sink on master). This made the issue go away.
Because I assumed that building against an older version of OBS might be the issue, I built the AUR package [2] based on obs-v4l2sink 0.1.0 against OBS 25.0.3 - same issue again.
This means to me, that whatever made it work on the master branches should be within this diff:
git diff 25.0.3..b9f7702378e1606a95bab4c4d62293a65039ac86git diff 0.1.0..1ec3c8ada0e1040d867ce567f177be55cd278378Looking at the diff, I don't spot anything obvious. Now I'm pretty much out of ideas.
[1] https://aur.archlinux.org/packages/obs-v4l2sink/ [2] https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=obs-v4l2sink
fenugrec
commented
4 years ago Hi, I might have some information to add . I've compiled debugging versions of obs-studio @ gdbb453d00 (current master), and obs-v4l2sink @ 1ec3c8ada0e1040d867ce567f177be55cd278378 (current master).
It seems the following happens:
libobs/obs-output.c:390 :
390 output->info.stop(output->context.data, ts);
that is resolved as v4l2sink_stop();
calls v4l2device_close();
segfaults on the close(out_data->v4l2_fd); line
When I debug, that fd is non-null; I can't tell if it was previously close'd somewhere just before ?
Or is it related to v4l2sink_videotick() using the fd after it being closed ? [EDIT] I tried to replace v4l2sink_videotick() with an empty function : still segfaults in v4l2device_close()
I also tried adding a close(out_data->v4l2_fd) at the end of v4l2device_open() to see if there was a problem with the V4L2 device itself but that didn't segfault.
fenugrec
commented
4 years ago Ok, my previous thoughts were wrong. Turns out the problem is the missing return in v4l2device_close() : that warning (fixed in PR #21 ) is actually undefined behavior. Compare the disassembly below. In both cases v4l2device_close() is inlined within v4l2sink_stop(), but when that return is removed it breaks the function completely.
************ WITHOUT a return statement *********
.text:0000000000005450 ; void __fastcall v4l2sink_stop(void *data, uint64_t ts)
.text:0000000000005450 _ZL13v4l2sink_stopPvm proc near
.text:0000000000005450 ts = rsi ; uint64_t
.text:0000000000005450 out_data = rdi ; v4l2sink_data *
......... obs_output_end_data_capture(out_data->output);
.text:0000000000005457 53 push rbx
.text:0000000000005458 48 89 FB mov rbx, out_data
.text:000000000000545B C6 47 08 00 mov byte ptr [out_data+8], 0
.text:000000000000545F 48 8B 3F mov out_data, [out_data]
.text:0000000000005462 out_data = rbx ; v4l2sink_data *
.text:0000000000005462 FF 15 D8 58+ call cs:obs_output_end_data_capture_ptr
.......... printf("stop pdata=%p, fd=%p\n", data, out_data->v4l2_fd); // temp debugging
.text:0000000000005462 00 00
.text:0000000000005468 48 8D 3D C7+ lea rdi, format ; "stop pdata=%p, fd=%p\n"
.text:0000000000005468 2C 00 00
.text:000000000000546F 48 89 DE mov rsi, out_data
.text:0000000000005472 31 C0 xor eax, eax
.text:0000000000005474 8B 53 0C mov edx, [out_data+0Ch]
.text:0000000000005477 FF 15 1B 59+ call cs:printf_ptr
...........v4l2device_close(data);
.text:0000000000005477 00 00
.text:000000000000547D 8B 7B 0C mov edi, [out_data+0Ch] ; fd
.text:0000000000005480 FF 15 6A 59+ call cs:close_ptr
.text:0000000000005480 00 00 ; } // starts at 5450
.......... undefined behavior. No idea what this is even supposed to be, but it doesn't work.
.text:0000000000005480 _ZL13v4l2sink_stopPvm endp
.text:0000000000005480
.text:0000000000005486 db 2Eh
.text:0000000000005486 66 2E 0F 1F+ nop word ptr [rax+rax+00000000h]
.text:0000000000005486 84 00 00 00+
.text:0000000000005486 00 00
************ WITH a return statement ************
text:0000000000005EF0 ; void __fastcall v4l2sink_stop(void *data, uint64_t ts)
.text:0000000000005EF0 _ZL13v4l2sink_stopPvm proc near
.text:0000000000005EF0 ts = rsi ; uint64_t
.text:0000000000005EF0 out_data = rdi ; v4l2sink_data *
......... obs_output_end_data_capture(out_data->output);
.text:0000000000005F00 53 push rbx
.text:0000000000005F01 48 89 FB mov rbx, out_data
.text:0000000000005F04 C6 47 08 00 mov byte ptr [out_data+8], 0
.text:0000000000005F08 48 8B 3F mov out_data, [out_data]
.text:0000000000005F0B out_data = rbx ; v4l2sink_data *
.text:0000000000005F0B FF 15 2F 4E+ call cs:obs_output_end_data_capture_ptr
.......... printf("stop pdata=%p, fd=%p\n", data, out_data->v4l2_fd); // temp debugging
.text:0000000000005F0B 00 00
.text:0000000000005F11 48 89 DE mov rsi, out_data
.text:0000000000005F14 48 8D 3D 01+ lea rdi, format ; "stop pdata=%p, fd=%p\n"
.text:0000000000005F14 23 00 00
.text:0000000000005F1B 31 C0 xor eax, eax
.text:0000000000005F1D 8B 53 0C mov edx, [out_data+0Ch]
.text:0000000000005F20 FF 15 72 4E+ call cs:printf_ptr
...........v4l2device_close(data);
.text:0000000000005F20 00 00
.text:0000000000005F26 8B 7B 0C mov edi, [out_data+0Ch] ; fd
.text:0000000000005F29 FF 15 C1 4E+ call cs:close_ptr
.text:0000000000005F29 00 00
...........v4l2sink_signal_stop("stop", false);
.text:0000000000005F2F 31 F6 xor esi, esi ; opening
.text:0000000000005F31 48 8D 3D A0+ lea rdi, msg ; "stop"
.text:0000000000005F31 23 00 00
.text:0000000000005F38 5B pop out_data
.text:0000000000005F39 FF 25 39 4E+ jmp cs:_Z20v4l2sink_signal_stopPKcb_ptr ; v4l2sink_signal_stop(char const*,bool)
.text:0000000000005F39 00 00 ; } // starts at 5EF0
.text:0000000000005F39 _ZL13v4l2sink_stopPvm endpTL;DR summary: just merge PR #21 !
kautsig
commented
4 years ago @fenugrec Awesome!
But this means my debugging above was wrong. It could be that I fixed the warning along the way, not knowing this could cause the issue. I should definitely stay away from C code. 😅
Hi, first of all, thanks for the great plugin. Currently the V4l2 Sink will crash my
OBS Studio 23.0.1-1on Arch Linux (Linux laptop 5.0.0-arch1-1-ARCH #1 SMP PREEMPT Mon Mar 4 14:11:43 UTC 2019 x86_64 GNU/Linux), when I press thestopbutton (reproducable every time). Because of this I can not change any video settings as OBS will always think a output is currently active (I guess?).This is the backtrace from running it in gdb:
Let me know if I can provide any additional data.