QT 5.7与Bluez 5.47连接设备时出现Segmentation Fault求助

Let's break down your issue and walk through targeted fixes based on the crash trace and your setup details:

Background #

You've worked past the initial gcc 7 compilation bug, but now hit a segmentation fault when running build/ankicar. The crash occurs inside QLowEnergyController::connectToDevice(), pointing to a compatibility or configuration issue between Qt Bluetooth and your BlueZ setup.

Crash Trace #

#0 0x00007ffff7931ccb in QLowEnergyController::connectToDevice() () from /usr/lib/x86_64-linux-gnu/libQt5Bluetooth.so.5 No symbol table info available. 
#1 0x00005555555718cc in AnkiCar::reconnect (this=0x5555557a82d0) at src/ankicar.cpp:444 No locals. 
#2 0x00005555555654b3 in DriveMode::requestBatteryUpdate (this=0x5555557a6400) at src/drivemode.cpp:102 
racecar = 0x5555557a82d0 
_container_ = {c = {<QListSpecialMethods<Racecar*>> = {<No data fields>}, {p = {static shared_null = {ref = {atomic = {_q_value = {<std::__atomic_base<int>> = {static _S_alignment = 4, _M_i = -1}, <No data fields>}}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, d = 0x5555557a85a0}, d = 0x5555557a85a0}}, i = {i = 0x5555557a85b8}, e = {i = 0x5555557a85d0}, control = 1} 
#3 0x00005555555768df in DriveMode::qt_static_metacall (_o=0x5555557a6400, _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0x7fffffffdf20) at moc_drivemode.cpp:156 
_t = 0x5555557a6400 
#4 0x00007ffff745f5b5 in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#5 0x00007ffff746c027 in QTimer::timeout(QTimer::QPrivateSignal) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#6 0x00007ffff746c388 in QTimer::timerEvent(QTimerEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#7 0x00007ffff74600db in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#8 0x00007ffff7430991 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#9 0x00007ffff7488d8e in QTimerInfoList::activateTimers() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#10 0x00007ffff7489551 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#11 0x00007ffff5002287 in g_main_context_dispatch () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 No symbol table info available. 
#12 0x00007ffff50024c0 in ?? () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 No symbol table info available. 
#13 0x00007ffff500254c in g_main_context_iteration () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 No symbol table info available. 
#14 0x00007ffff74898ef in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#15 0x00007ffff742e9ea in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#16 0x00007ffff7437a84 in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 No symbol table info available. 
#17 0x000055555555b42e in main (argc=1, argv=0x7fffffffe468) at src/main.cpp:29 
a = <incomplete type>

Potential Fixes #

1. Ensure BlueZ Experimental Mode is Fully Activated #

You compiled BlueZ with --enable-experimental, but the service might not be using these features yet:

• Edit /lib/systemd/system/bluetooth.service and update the ExecStart line to:

  ExecStart=/usr/lib/bluetooth/bluetoothd --experimental
  

• Reload the daemon and restart Bluetooth:

  sudo systemctl daemon-reload
  sudo systemctl restart bluetooth
  

• Verify experimental mode is active:

  bluetoothctl show | grep Features
  

  You should see ExperimentalFeatures listed in the output.

2. Downgrade BlueZ to the Project-Specified 5.42 Version #

The project documentation explicitly references BlueZ 5.42. Newer versions like 5.47 may have API changes that break compatibility with Kubuntu 18.04's default Qt 5.9.x Bluetooth bindings. To downgrade:

• Uninstall your current BlueZ version:

  sudo apt remove --purge bluez
  

• Download, compile, and install BlueZ 5.42 with your required flags:

  wget https://www.kernel.org/pub/linux/bluetooth/bluez-5.42.tar.xz
  tar xf bluez-5.42.tar.xz
  cd bluez-5.42
  ./configure --prefix=/usr --mandir=/usr/share/man --sysconfdir=/etc --localstatedir=/var --enable-experimental --enable-maintainer-mode
  make
  sudo make install
  

• Restart the Bluetooth service after installation.

3. Enable Qt Bluetooth Debug Logs #

Get more context about what's failing before the crash by enabling debug logging:

• Run your application with this environment variable set:

  QT_LOGGING_RULES="qt.bluetooth*=true" ./build/ankicar
  

  The logs may reveal issues like failed device discovery, invalid controller handles, or permission errors.

4. Check User Bluetooth Permissions #

Ensure your user has the necessary access to Bluetooth devices:

• Add your user to the bluetooth group:

  sudo usermod -aG bluetooth $USER
  

• Log out and back in for the changes to take effect.

5. Inspect the AnkiCar::reconnect Implementation #

The crash happens in AnkiCar::reconnect at line 444 of src/ankicar.cpp. Double-check that the QLowEnergyController instance being used is valid (not a dangling pointer) before calling connectToDevice(). It's possible the controller was deleted or not properly initialized prior to this call.

内容的提问来源于stack exchange，提问作者Renji