Invocations of qdbus from the widget (window move, shortcut getting) causes qdbus to SIGSEGV

[ArtyIF]

Since yesterday, I've been getting qdbus crashes when I'm dragging windows with this widget. At first I wasn't sure what was causing it (I figured out while writing the report, so sorry for being so stream-of-consciousness-y), but it began when I was testing some DVDs I had lying around, and I thought it was related to that. But I unplugged the drive, rebooted my computer several times, and narrowed it down to this widget. The crash happens both in 0.8.7 (KDE Store version) and 0.9.0 (GitHub version). Opening the widget settings also causes a crash, but it also says this: Unable to update KWin shortcuts: ''

The crash notification:

Crash details:

           PID: 7059 (qdbus)
           UID: 1000 (artyif)
           GID: 1000 (artyif)
        Signal: 11 (SEGV)
     Timestamp: Sat 2026-03-28 15:34:58 MSK (10s ago)
  Command Line: /usr/lib/qt6/bin/qdbus org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component.invokeShortcut $'Window Move'
    Executable: /usr/lib/qt6/bin/qdbus
 Control Group: /user.slice/user-1000.slice/user@1000.service/session.slice/plasma-plasmashell.service
          Unit: user@1000.service
     User Unit: plasma-plasmashell.service
         Slice: user-1000.slice
     Owner UID: 1000 (artyif)
       Boot ID: 00197f5b7edc438fa7694d3717c9f79a
    Machine ID: a9590a6afc4d4e40a757f61e3095c8b7
      Hostname: artyif-desktop
       Storage: /var/lib/systemd/coredump/core.qdbus.1000.00197f5b7edc438fa7694d3717c9f79a.7059.1774701298000000.zst (present)
  Size on Disk: 192.5K
       Message: Process 7059 (qdbus) of user 1000 dumped core.
                
                Stack trace of thread 7059:
                #0  0x00007fea844a74d1 n/a (libQt6Core.so.6 + 0xa74d1)
                #1  0x00007fea84c739eb n/a (libQt6DBus.so.6 + 0x5e9eb)
                #2  0x00007fea83e4fa61 n/a (libc.so.6 + 0x40a61)
                #3  0x00007fea83e4fb3e exit (libc.so.6 + 0x40b3e)
                #4  0x00007fea83e366c8 n/a (libc.so.6 + 0x276c8)
                #5  0x00007fea83e367f9 __libc_start_main (libc.so.6 + 0x277f9)
                #6  0x00005594472f1745 n/a (/usr/lib/qt6/bin/qdbus + 0x6745)
                
                Stack trace of thread 7060:
                #0  0x00007fea83eadf32 n/a (libc.so.6 + 0x9ef32)
                #1  0x00007fea83ea239c n/a (libc.so.6 + 0x9339c)
                #2  0x00007fea83ea23e4 n/a (libc.so.6 + 0x933e4)
                #3  0x00007fea83f1c2f6 ppoll (libc.so.6 + 0x10d2f6)
                #4  0x00007fea84308744 n/a (libglib-2.0.so.0 + 0x60744)
                #5  0x00007fea84308825 g_main_context_iteration (libglib-2.0.so.0 + 0x60825)
                #6  0x00007fea84872222 _ZN20QEventDispatcherGlib13processEventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE (libQt6Core.so.6 + 0x472222)
                #7  0x00007fea845845d6 _ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE (libQt6Core.so.6 + 0x1845d6)
                #8  0x00007fea8469efa2 _ZN7QThread4execEv (libQt6Core.so.6 + 0x29efa2)
                #9  0x00007fea84c4c50e n/a (libQt6DBus.so.6 + 0x3750e)
                #10 0x00007fea8474d483 n/a (libQt6Core.so.6 + 0x34d483)
                #11 0x00007fea83ea597a n/a (libc.so.6 + 0x9697a)
                #12 0x00007fea83f292bc n/a (libc.so.6 + 0x11a2bc)
                ELF object binary architecture: AMD x86-64

Running the command shown in the Command Line: section also causes the SEGV, but running just qdbus instead (which links to /usr/bin/qdbus) avoids any crashes. The command line for the error from opening the settings is /usr/lib/qt6/bin/qdbus org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component.shortcutNames. I think, at least for Arch, whatever path for qdbus is used needs to be replaced with /usr/bin/qdbus.

System details:

Operating System: Arch Linux 
KDE Plasma Version: 6.6.3
KDE Frameworks Version: 6.24.0
Qt Version: 6.11.0
Kernel Version: 6.19.9-zen1-1-zen (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5700X 8-Core Processor
Memory: 32 GiB of RAM (31.2 GiB usable)
Graphics Processor: AMD Radeon RX 570 Series

[ArtyIF]

Looking into it further, it seems like some sort of a mismatch between KDE and Qt's versions. It works fine on my Fedora KDE install, which still uses Qt 6.10.x. I replicated the SIGSEGV on a brand new Arch install with Qt 6.11, maybe I should report this to the packagers too somehow, but I don't know where.

[luisbocanegra]

Someone already reported it https://gitlab.archlinux.org/archlinux/packaging/packages/qt6-tools/-/work_items/4 and also to Qt https://qt-project.atlassian.net/browse/QTBUG-145333

[antroids]

Hi, could you check the 0.9.1.
Update instructions: https://github.com/antroids/application-title-bar?tab=readme-ov-file#installing
I've lowered priority for "/usr/lib/qt6/bin/qdbus", so "qdbus" should be selected.

[zierf]

Unfortunately, the workaround for application-title-bar does not work on all systems, because it's still selecting /run/current-system/sw/bin/qdbus on NixOS, which is the QT6 one. The error itself ultimately lies in qtbase.

On NixOS, the problem can be solved with an overlay if you don't want to wait for upstream and are willing to recompile many packages over a longer period of time.
NixOS/nixpkgs#517705 (comment)

---

Judging by the Arch ticket, it seems they have to wait for the official fix with QT v6.12.

At least the status there was marked as waiting-upstream and the tickets were subsequently closed.

[antroids]

Does it crash on NixOS even when the qdbus command is used?
Is there a qdbus utility compatible with the OS somewhere?

[zierf]

The answer is yes, it crashes reproducibly with some affected commands, but it does not crash with all available commands. Since the system continued to run smoothly apart from this one crash notification, most dbus commands appear to be ok.

Unfortunately, the error message only shows the problematic DBus call and not which application caused it, so it was difficult to find the right one until I came across the information in the issues.

It's not a bug in this widget, just bad luck that it uses a DBus call which is falls under this QT bug.
And it's not on NixOS only, it should occur on all KDE desktops using QT v6.11.

---

I don't know exactly what all falls under QDBusMetaObject: ensure custom types are normalized, but this happens with all commands to qdbus that actually require this normalization mentioned here.

I was able to reliably reproduce the crash in two variations. Once shortly after loading the desktop, with the exact error from the original post above asking for shortcuts at org.kde.kglobalaccel.

The second command was the one from qdbus6 segfaults in version 6.11.0-1.

# crashed before patch
$> qdbus org.freedesktop.portal.Desktop /org/freedesktop/portal/desktop org.freedesktop.portal.Settings.Read "org.freedesktop.appearance" "color-scheme"

1
zsh: segmentation fault (core dumped)  qdbus org.freedesktop.portal.Desktop /org/freedesktop/portal/desktop

As far as I can see, the only qdbus that can be found via $PATH in NixOS is the one from qttools.

# fine after patch
$> qdbus org.freedesktop.portal.Desktop /org/freedesktop/portal/desktop org.freedesktop.portal.Settings.Read "org.freedesktop.appearance" "color-scheme"

1

I only found qdbus command crashes on exit in QMetaType::unregisterMetaType later and hadn't tried it before installing the patch on my system. Since QT v6.12 has not yet been released and Arch probably won't patch it out beforehand, the command should also generate a dbus error and @ArtyIF should be able to confirm this on his Arch system, unless your widget can find an alternative DBus name/location you listed in 7a1f0ef.

# fine after patch
$> qdbus --system org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager.CanPowerOff

yes

---

As far as I can see, the only qdbus that can be found via $PATH in NixOS is the one from qttools and autocompletion doesn't show qdbus6 or qdbus-qt6.

Because NixOS is not FHS compliant, other potentially common extra paths like /usr/lib/qt6/bin/qdbus are also missing, which should be the case for other non-FHS systems as well. However, it is well suited for injecting specific changes using overlays (apart from the long wait time due to the necessary recompilation of qtbase and its dependent packages).

[luisbocanegra]

Since QT v6.12 has not yet been released and Arch probably won't patch it out beforehand

I think they did? Trying qdbus6 org.freedesktop.portal.Desktop /org/freedesktop/portal/desktop org.freedesktop.portal.Settings.Read "org.freedesktop.appearance" "color-scheme" no longer crashes. According to this it was fixed in 6.11.1 too https://qt-project.atlassian.net/browse/QTBUG-145359

Also, at least on Arch qdbus (/usr/bin/qdbus) is the Qt5 version, and qdbus6 (/usr/bin/qdbus6 -> ../lib/qt6/bin/qdbus) is the Qt6 counterpart, it can be confirmed by checking which package owns the file or using ldd.

---

The whole qdbus name variations and not being in PATH was the reason I moved my projects to gdbus which is provided by glib2 and AFAIK is available on every KDE install

[zierf]

Then a new version with the patch for Arch with v6.11.1 was released slightly earlier than expected; I had overlooked it on the site (only stumbled across it late) and it simply wasn't obvious in the other listings. Nevertheless, it wasn't patched early by Arch, but they waited for an upstream QT update, luckily a fast one.

---

gdbus is not necessarily found in every KDE installation. Programs that require a specific dbus (such as gdbus or that of KDE5) may link directly to the specific library, but only the KDE6 one is discoverable in PATH.

The QT update was the right and important solution to the problem (which was also caused there), but that should not diminish the attempt to solve it in advance on the widget side.

[acomagu]

Maybe busctl command can be used as alternative for qdbus?

I didn't know this command, but busctl seems to be installed as part of systemd.

In my NixOS env, this crashes:

qdbus org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component.shortcutNames

But this doesn't crash:

busctl --user call org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component shortcutNames

To match the output format of the original command:

busctl --user -j call org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component shortcutNames | jq -r .data[0][]

[NovaViper]

@acomagu This could work, maybe can have this as a fallback? At least for the time being.

[acomagu]

@NovaViper I've attached my nix module including the patch. It's working well so far in my environment.

My nix module:

{ pkgs, ... }:
{
  nixpkgs.overlays = [
    (final: prev: {
      application-title-bar = prev.application-title-bar.overrideAttrs (old: {
        # Replace qdbus calls with busctl to avoid qdbus crashes on Qt 6.11.
        # https://github.com/antroids/application-title-bar/issues/91
        postPatch = (old.postPatch or "") + ''
          qml=package/contents/ui/KWinConfig.qml

          substituteInPlace "$qml" \
            --replace-fail 'property string reconfigureCommand: qdbusCommandName !== "" ? qdbusCommandName + " org.kde.KWin /KWin reconfigure" : ""' \
                           'property string reconfigureCommand: "${final.systemd}/bin/busctl --user call org.kde.KWin /KWin org.kde.KWin reconfigure"' \
            --replace-fail 'property string getAllKWinShortcutNamesCommand: qdbusCommandName !== "" ? qdbusCommandName + " org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component.shortcutNames" : ""' \
                           'property string getAllKWinShortcutNamesCommand: "${final.systemd}/bin/busctl --user --json=short call org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component shortcutNames | ${final.jq}/bin/jq -r \".data[0][]\""' \
            --replace-fail 'property string invokeKWinShortcutCommand: qdbusCommandName !== "" ? qdbusCommandName + " org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component.invokeShortcut " : ""' \
                           'property string invokeKWinShortcutCommand: "${final.systemd}/bin/busctl --user call org.kde.kglobalaccel /component/kwin org.kde.kglobalaccel.Component invokeShortcut s "' \
            --replace-fail 'property string qdbusCommandName: "qdbus"' \
                           'property string qdbusCommandName: "${final.systemd}/bin/busctl"'

          sed -i '/function updateQdbusCommandName()/,/^    }$/c\
              function updateQdbusCommandName() {\
                  qdbusCommandNameChanged();\
              }' "$qml"
        '';
      });
    })
  ];

  environment.systemPackages = [
    pkgs.application-title-bar
  ];
}

(This patch is somewhat messy. I think at least removing jq dependency are needed to rewrite this patch to the upstream level)

[antroids]

Hi,
What about https://github.com/antroids/application-title-bar/releases/tag/v0.10.0 ?
Could you please test it in your environments.
I've removed qdbus* utilities usages.