Segmentation fault on Archlinux Arm

[tinytempmouse]

When ever I try to launch anything to do with Kvantum eg kvantummanager I get a segmentation fault (core dumped) error. I'm stumped what to do to fix this. I'm running arch Linux arm 6.6.42.

Aug 13 15:52:19 tinymouse sudo[8506]: pam_systemd_home(sudo:auth): New sd-bus connection (system-bus-pam-systemd-home-8506) opened.
Aug 13 15:52:23 tinymouse sudo[8506]: tinymouse : TTY=pts/0 ; PWD=/home/tinymouse ; USER=root ; COMMAND=/usr/bin/pacman --sync -- g>
Aug 13 15:52:23 tinymouse sudo[8506]: pam_unix(sudo:session): session opened for user root(uid=0) by tinymouse(uid=1000)
Aug 13 15:53:07 tinymouse sudo[8506]: pam_unix(sudo:session): session closed for user root
Aug 13 15:53:18 tinymouse systemd-coredump[8693]: Process 8689 (kvantummanager) of user 1000 terminated abnormally with signal 11/S>
Aug 13 15:53:18 tinymouse systemd[1]: Started Process Core Dump (PID 8693/UID 0).
Aug 13 15:53:19 tinymouse systemd-coredump[8694]: [🡕] Process 8689 (kvantummanager) of user 1000 dumped core.
 
                                                  Stack trace of thread 8689:
                                                  #0  0x0000007f819bd920 n/a (libQt6Core.so.6 + 0x2ad920)
                                                  #1  0x0000007f819bdb34 _ZN7QString14toLower_helperERKS_ (libQt6Core.so.6 + 0x2adb>
                                                  #2  0x0000007f818c3604 n/a (libQt6Core.so.6 + 0x1b3604)
                                                  #3  0x0000007f818c73b8 _ZN9QMetaType7convertES_PKvS_Pv (libQt6Core.so.6 + 0x1b73b>
                                                  #4  0x0000007f819220c0 _ZNK8QVariant6toBoolEv (libQt6Core.so.6 + 0x2120c0)
                                                  #5  0x0000007f7c4876b8 _ZN7Kvantum11ThemeConfig12getFrameSpecERK7QString (libkvan>
                                                  #6  0x0000007f7c3f5ee0 _ZNK7Kvantum5Style11pixelMetricEN6QStyle11PixelMetricEPK12>
                                                  #7  0x0000007f82b506f8 n/a (libQt6Widgets.so.6 + 0x3406f8)
                                                  #8  0x0000007f82b5a624 n/a (libQt6Widgets.so.6 + 0x34a624)
                                                  #9  0x0000007f82b5244c _ZN9QLineEditC1EP7QWidget (libQt6Widgets.so.6 + 0x34244c)
                                                  #10 0x0000005582a1e810 n/a (kvantummanager + 0x4e810)
                                                  #11 0x00000055829fc184 n/a (kvantummanager + 0x2c184)
                                                  #12 0x00000055829de2bc n/a (kvantummanager + 0xe2bc)
                                                  #13 0x0000007f81288294 n/a (libc.so.6 + 0x28294)
                                                  #14 0x0000007f81288378 __libc_start_main (libc.so.6 + 0x28378)
                                                  #15 0x00000055829df1b0 n/a (kvantummanager + 0xf1b0)
 
                                                  Stack trace of thread 8691:
                                                  #0  0x0000007f812e6b9c n/a (libc.so.6 + 0x86b9c)
                                                  #1  0x0000007f812e9828 pthread_cond_wait (libc.so.6 + 0x89828)
                                                  #2  0x0000007f81a898c8 _ZN14QWaitCondition4waitEP6QMutex14QDeadlineTimer (libQt6C>
                                                  #3  0x0000007f7d9004b4 n/a (libQt6WaylandClient.so.6 + 0x804b4)
                                                  #4  0x0000007f81a7a674 n/a (libQt6Core.so.6 + 0x36a674)
                                                  #5  0x0000007f812ea624 n/a (libc.so.6 + 0x8a624)
                                                  #6  0x0000007f8135064c n/a (libc.so.6 + 0xf064c)
 
                                                  Stack trace of thread 8690:
                                                  #0  0x0000007f81345ccc __poll (libc.so.6 + 0xe5ccc)
                                                  #1  0x0000007f80e5bfd4 n/a (libglib-2.0.so.0 + 0x6bfd4)
                                                  #2  0x0000007f80e5c924 g_main_context_iteration (libglib-2.0.so.0 + 0x6c924)
                                                  #3  0x0000007f81bcd24c _ZN20QEventDispatcherGlib13processEventsE6QFlagsIN10QEvent>
                                                  #4  0x0000007f8189a670 _ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE (lib>
                                                  #5  0x0000007f819d6770 _ZN7QThread4execEv (libQt6Core.so.6 + 0x2c6770)
                                                  #6  0x0000007f80d2f984 n/a (libQt6DBus.so.6 + 0x3f984)
                                                  #7  0x0000007f81a7a674 n/a (libQt6Core.so.6 + 0x36a674)
                                                  #8  0x0000007f812ea624 n/a (libc.so.6 + 0x8a624)
                                                  #9  0x0000007f8135064c n/a (libc.so.6 + 0xf064c)
 
                                                  Stack trace of thread 8692:
                                                  #0  0x0000007f81345ccc __poll (libc.so.6 + 0xe5ccc)
                                                  #1  0x0000007f7d900518 n/a (libQt6WaylandClient.so.6 + 0x80518)
                                                  #2  0x0000007f81a7a674 n/a (libQt6Core.so.6 + 0x36a674)
                                                  #3  0x0000007f812ea624 n/a (libc.so.6 + 0x8a624)
                                                  #4  0x0000007f8135064c n/a (libc.so.6 + 0xf064c)
                                                  ELF object binary architecture: AARCH64
Aug 13 15:53:19 tinymouse systemd[1]: [email protected]: Deactivated successfully.
Aug 13 15:53:19 tinymouse systemd[1]: [email protected]: Consumed 1.387s CPU time.

[tsujan]

Not reproducible, of course.

You need to be more specific. Which version of Kvanrum? How did you install Kvantum? Did you compile it? Against which version of Qt? What's the "platform theme" you use to activate Kvantum (inside /usr/lib/qt6/plugins/platformthemes)? etc.

[tinytempmouse]

Kvantum 1.1.2-1 (tried both compiled and from package manager)
Qt6 6.7.2-1

[tsujan]

I wonder if this can be related to arm and its packages. There's nothing in Kvantum that makes a distinction.

More info is needed.

[tsujan]

Closing because there's nothing in Kvantum that can cause this crash, especially in an elementary method like QVariant::toBool(). The cause should be deeper.

The report might be reopened if more info is provided, such that the issue can be reproduced.

[xiaohuirong]

I also encountered this issue on Archlinux Arm aarch64.

#0  0x0000ffff8f05d920 in ??? () at /usr/lib/libQt6Core.so.6
#1  0x0000ffff8f05db34 in QString::toLower_helper(QString const&) () at /usr/lib/libQt6Core.so.6
#2  0x0000ffff8ef63604 in ??? () at /usr/lib/libQt6Core.so.6
#3  0x0000ffff8ef673b8 in QMetaType::convert(QMetaType, void const*, QMetaType, void*) () at /usr/lib/libQt6Core.so.6
#4  0x0000ffff8efc20c0 in QVariant::toBool() const () at /usr/lib/libQt6Core.so.6
#5  0x0000ffff844f76b8 in Kvantum::ThemeConfig::getFrameSpec(QString const&) ()
    at /usr/lib/qt6/plugins/styles/libkvantum.so
#6  0x0000ffff84449420 in Kvantum::Style::Style(bool) () at /usr/lib/qt6/plugins/styles/libkvantum.so
#7  0x0000ffff844e664c in Kvantum::KvantumPlugin::create(QString const&) ()
    at /usr/lib/qt6/plugins/styles/libkvantum.so
#8  0x0000ffff9019e190 in QStyleFactory::create(QString const&) () at /usr/lib/libQt6Widgets.so.6
#9  0x0000ffff84553abc in ??? () at /usr/lib/qt6/plugins/styles/libqt6ct-style.so
#10 0x0000ffff84553e38 in ??? () at /usr/lib/qt6/plugins/styles/libqt6ct-style.so
#11 0x0000ffff84553300 in ??? () at /usr/lib/qt6/plugins/styles/libqt6ct-style.so
#12 0x0000ffff9019e190 in QStyleFactory::create(QString const&) () at /usr/lib/libQt6Widgets.so.6
#13 0x0000ffff900f279c in QApplication::style() () at /usr/lib/libQt6Widgets.so.6
#14 0x0000ffff900f2fd8 in QApplicationPrivate::initialize() () at /usr/lib/libQt6Widgets.so.6
#15 0x0000ffff900f339c in QApplicationPrivate::init() () at /usr/lib/libQt6Widgets.so.6
#16 0x0000aaaab74e4070 in ??? ()
#17 0x0000ffff8e968294 in ??? () at /usr/lib/libc.so.6
#18 0x0000ffff8e968378 in __libc_start_main () at /usr/lib/libc.so.6
#19 0x0000aaaab74e4a70 in ??? ()

Raspberry Pi 4 Model B Rev 1.2
Qt6: 6.7.2-1
Kvantum: 1.1.2-1

[tsujan]

@xiaohuirong, thanks for your clean backtrace!

Since you also use Arm, this confirms my suspicion about a problem in it (but doesn't prove it).

Everything will change if someone with x86_64 packages encounters the same issue — although I don't know how that might be possible because, first, I have it and see no problem, and second, the crash happens in a very basic Qt method.

[xiaohuirong]

After downgrading Kvantum to 1.1.0-1, it no longer crashes.

[tsujan]

Because nothing has changed regarding the backtrace from 1.1.0 to 1.1.2 (see V1.1.0...V1.1.2), the problem may be in the kvantum aarch64 package for 1.1.2.

[xiaohuirong]

This is likely an issue with Qt6. The 1.1.0-1 version I recompiled doesn't work, but the 1.1.0-1 version downloaded from the archive works.

[tsujan]

This is likely an issue with Qt6

That's possible. But there's also another possibility: the compiler itself.

[tsujan]

I changed the report to a Q&A discussion for more visibility.

[chiyuki0325]

I added a line of qDebug() before ThemeConfig.cpp#164 to print the contents of QVariant v, and then Kvantum miraculously worked... so this is likely an undefined behavior inside Qt.
However, if I build clean Kvantum sources with Undefined Behavior Sanitizer enabled, it works very normally without any errors printed.

I don't understand those underlying things and don't know how to continue debugging this issue 🤔

[chiyuki0325]

Judging from the output of gdb, this error seems to be caused by a toBool operation on an uninitialized QVariant (QVariant(Invalid)). However I cannot reproduce this crash outside of Kvantum...

The following code will print false normally:

QVariant v;
qDebug() << v.toBool();

[tsujan]

Judging from the output of gdb, this error seems to be caused by a toBool operation on an uninitialized QVariant

The constructor of QVariant makes a variant with the storage type QMetaType::UnknownType (the so-called "invalid" variant). And QVariant::toBool() is false for this storage type (→ https://doc.qt.io/qt-6/qvariant.html#toBool). So, there's nothing undefined.

[chiyuki0325]

I tried to rebuild the Kvantum package with Clang and then it worked. This issue is most likely caused by GCC itself.

[tsujan]

@chiyuki0325, you also use Arm; don't you?

[chiyuki0325]

@chiyuki0325, you also use Arm; don't you?

Yes, clang on arm64 works