I enabled vlc-9999 in order to use Qt6, and it loads/plays videos just fine. However, when trying to play .mkv files with opus audio, I get an error about an "unsupported media format." So I compile vlc with USE="opus", and now vlc segfaults on startup with the following error reported to dmesg: --------------- vlc-qt[8044]: segfault at 8 ip 00007f8033dde2a8 sp 00007f804095b340 error 4 in libQt6Quick.so.6.8.1[4e62a8,7f8033a0b000+423000] likely on CPU 5 (core 5, socket 0) [11219.359122] Code: 00 00 48 83 c4 10 5b 5d 41 5c c3 90 66 0f 1f 44 00 00 f3 0f 1e fa 55 48 89 e5 41 55 41 54 53 48 83 e4 e0 49 89 fc 48 83 c4 80 <48> 8b 5f 08 64 4c 8b 2c 25 28 00 00 00 4c 89 6c 24 78 49 89 f5 c5 --------------- libQt6Quick belongs to qtdeclarative; remerging that package does not seem to help. --------------- # emerge -pv vlc These are the packages that would be merged, in order: Calculating dependencies... done! Dependency resolution took 3.48 s (backtrack: 0/20). [ebuild R *] media-video/vlc-9999:0/12-9::gentoo USE="X a52 alsa cddb dbus dvbpsi dvd encode ffmpeg flac fontconfig gcrypt gstreamer gui ieee1394 jack jpeg libsamplerate mad matroska mp3 mpeg ncurses ogg opus png speex ssl svg theora truetype udev vdpau x264 xml -aom -archive -aribsub -bidi -bluray -chromaprint -chromecast -dav1d -dc1394 -debug (-directx) -dts -faad -fdk -fluidsynth -gme -kate -keyring -kms -libass -libcaca -libnotify -libplacebo -libtar -libtiger -linsys -lirc -live -loudness -lua -macosx-notifications -modplug -mtp -musepack -nfs -omxil -optimisememory -projectm -pulseaudio -rdp -run-as-root -samba -sdl-image -sftp -shout -sid -skins -soxr -srt -taglib -test -tremor -twolame -upnp -v4l -vaapi -vnc -vpx -wayland -x265 -zeroconf -zvbi" CPU_FLAGS_X86="mmx sse" LUA_SINGLE_TARGET="lua5-1" 0 KiB Reproducible: Always Steps to Reproduce: 1. emerge vlc-9999 with USE="opus" 2. try to start vlc 3. segfault in libQt6Quick # emerge --info Portage 3.0.67 (python 3.13.1-final-0, default/linux/amd64/23.0/split-usr, gcc-14, glibc-2.40-r7, 6.13.0-gentoo x86_64) ================================================================= System uname: Linux-6.13.0-gentoo-x86_64-AMD_Ryzen_7_3800X_8-Core_Processor-with-glibc2.40 KiB Mem: 32777188 total, 18885172 free KiB Swap: 3145716 total, 3145716 free Timestamp of repository gentoo: Sat, 25 Jan 2025 07:05:03 +0000 Head commit of repository gentoo: 158f67e948fa81dc13b6f07245c76739d6031438 Timestamp of repository guru: Thu, 23 Jan 2025 15:48:56 +0000 Head commit of repository guru: 614ad53328d8023035c6415f59e3476fad2d4b7a Timestamp of repository pentoo: Sat, 25 Jan 2025 06:49:49 +0000 Head commit of repository pentoo: ad4264738579e2cc33d0f02eec9b818d9f399cc7 Timestamp of repository ppfeufer-gentoo-overlay: Wed, 22 Jan 2025 13:04:09 +0000 Head commit of repository ppfeufer-gentoo-overlay: eae0c670db5ee338ca3872408fa9097809c74437 Timestamp of repository steam-overlay: Thu, 16 Jan 2025 14:18:14 +0000 Head commit of repository 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UPDATE: it turns out it isn't USE="opus" that's the cause, because emerging vlc without opus support still results in a segfault. I *had* vlc-9999 running just before, and haven't changed anything about the system, so now I'm really not sure what's causing it :(
You'll likely need to take it upstream for something in a live ebuild, but I'm happy to take a quick look in case it's something obvious. Backtrace please? (https://wiki.gentoo.org/wiki/Debugging)
I can do that, but do I want to install debugging systems for and then backtrace vlc, or qtdeclarative?
here's gdb running vlc, giving the message it returned when it segfaulted: ------------------- Thread 8 "vlc-qt" received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7ffff28a86c0 (LWP 12933)] 0x00007ffff5f3a2a8 in QQuickItem::setSize(QSizeF const&) () from /usr/lib64/libQt6Quick.so.6 ------------------- It's possible that there was some commit between when I emerged vlc-9999 earlier this morning and the subsequent emerges that caused this. Should I also post this upstream?
(In reply to N. Andrew Walsh from comment #4) > here's gdb running vlc, giving the message it returned when it segfaulted: > Debug symbols for whatever provides qtquick and also vlc at least, but you may need more. > ------------------- > Thread 8 "vlc-qt" received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7ffff28a86c0 (LWP 12933)] > 0x00007ffff5f3a2a8 in QQuickItem::setSize(QSizeF const&) () from > /usr/lib64/libQt6Quick.so.6 > ------------------- > Please write 'bt' and then hit enter in the gdb prompt to get a full backtrace. > It's possible that there was some commit between when I emerged vlc-9999 > earlier this morning and the subsequent emerges that caused this. Should I > also post this upstream? Yes, but let's try get a full bt first, so we can make it easier for them
OK, here's the backtrace from vlc: -------------------- Thread 8 "vlc-qt" received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7ffff28a86c0 (LWP 3387)] 0x00007ffff5f3a2a8 in QQuickItem::setSize(QSizeF const&) () from /usr/lib64/libQt6Quick.so.6 (gdb) bt #0 0x00007ffff5f3a2a8 in QQuickItem::setSize(QSizeF const&) () from /usr/lib64/libQt6Quick.so.6 #1 0x00007ffff65003de in vlc::CompositorX11UISurface::updateSizes (this=this@entry=0x7fffec0f27a0) at maininterface/compositor_x11_uisurface.cpp:264 #2 0x00007ffff6500d85 in vlc::CompositorX11UISurface::eventFilter (this=0x7fffec0f27a0, event=0x7ffff28a76e0) at maininterface/compositor_x11_uisurface.cpp:325 #3 0x00007ffff3f80d64 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /usr/lib64/libQt6Core.so.6 #4 0x00007ffff57a7b09 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt6Widgets.so.6 #5 0x00007ffff3f81038 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib64/libQt6Core.so.6 #6 0x00007ffff4c3cb3e in QGuiApplicationPrivate::processGeometryChangeEvent(QWindowSystemInterfacePrivate::GeometryChangeEvent*) () from /usr/lib64/libQt6Gui.so.6 #7 0x00007ffff4c96b7f in ?? () from /usr/lib64/libQt6Gui.so.6 #8 0x00007ffff3f646dd in ?? () from /usr/lib64/libQt6Core.so.6 #9 0x00007ffff4c8ef03 in QWindow::screenChanged(QScreen*) () from /usr/lib64/libQt6Gui.so.6 #10 0x00007ffff4c8fc57 in QWindowPrivate::emitScreenChangedRecursion(QScreen*) () from /usr/lib64/libQt6Gui.so.6 #11 0x00007ffff64f8386 in restoreWindowPositionImpl (settings=<optimized out>, window=<optimized out>) at widgets/native/qvlcframe.cpp:116 #12 QVLCTools::restoreWindowPosition (settings=<optimized out>, window=0x7fffec0e7210, defSize=..., defPos=...) at widgets/native/qvlcframe.cpp:146 #13 0x00007ffff63bfe39 in InterfaceWindowHandler::InterfaceWindowHandler (this=0x7fffec4b19e0, _p_intf=<optimized out>, mainCtx=0x7fffec001bd0, window=0x7fffec0e7210, parent=<optimized out>) at maininterface/interface_window_handler.cpp:61 #14 0x00007ffff63bb8e0 in std::make_unique<InterfaceWindowHandler, qt_intf_t*&, MainCtx*&, QWindow*&> () at /usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/bits/unique_ptr.h:1076 #15 vlc::CompositorVideo::commonGUICreateImpl (this=this@entry=0x7fffec0e5b60, window=0x7fffec0e7210, flags=...) at maininterface/compositor.cpp:298 #16 0x00007ffff63bbafb in vlc::CompositorVideo::commonGUICreate (this=0x7fffec0e5b60, window=<optimized out>, qmlSurface=0x7fffec0f27c8, flags=...) at maininterface/compositor.cpp:345 #17 0x00007ffff64fbd75 in vlc::CompositorX11::makeMainInterface (this=0x7fffec0e5b60, mainCtx=<optimized out>) at maininterface/compositor_x11.cpp:209 #18 0x00007ffff62b9078 in Thread (obj=0x5555555d31b0) at qt.cpp:1033 #19 0x00007ffff7d0af38 in ?? () from /lib64/libc.so.6 --Type <RET> for more, q to quit, c to continue without paging-- #20 0x00007ffff7d7d4cc in ?? () from /lib64/libc.so.6 ----------------- I'm emerging qtdeclarative (the owner of qtquick) with debugsym, but I'll only post that output if it's any different from this. Cheers
Thanks for your efforts. Looks like https://code.videolan.org/videolan/vlc/-/issues/28880. I've no idea if they need to check if size() is valid or what in https://code.videolan.org/videolan/vlc/-/blob/master/modules/gui/qt/maininterface/compositor_x11_uisurface.cpp#L253. Per https://doc.qt.io/qt-6/qquickitem.html#setSize, it might need an isValid check? (but that's complete speculation and knowing nothing about Qt APIs really).
UPDATE: and now that I have some backtrace, I can see that there's a report on this issue at the vlc bug tracker: https://code.videolan.org/videolan/vlc/-/issues/28880
So we both came to the same conclusion, that it's an upstream bug. Alas! I'll have to wait on them to fix it, then. But thanks for helping me track down the issue. I guess I'll revert to the non-9999 version for now. Cheers.
Ah, I see on the upstream bug "The GUI fails to start, NULL pointer m_rootItem in vlc::CompositorX11UISurface::updateSizes". You could try add a hacky check in, even if it's not the right place for it. If you want to accelerate the upstream fix, I'd suggest building manually (though not required, see https://wiki.gentoo.org/wiki/Bisecting_with_live_ebuilds) to give a bisect result for what commit broke it and CC the author on the upstream bug.
The upstream report already lists the bisect point (or at least gives the bug as occurring "somewhere between" two commits. As for adding in some hacky check, it's not so important to me that I can't just revert to vlc3 and wait. I'll keep an eye on that bugreport and report back here if/when they fix it upstream. Thanks again!
