Bug 509386

Summary: Unable to compile functioning Qt application
Product: [Developer tools] Qt/KDE Flatpak Runtime Reporter: Rosalie <rosalie>
Component: generalAssignee: Aleix Pol <aleixpol>
Status: RESOLVED DOWNSTREAM    
Severity: normal CC: aacid, fella
Priority: NOR    
Version First Reported In: unspecified   
Target Milestone: ---   
Platform: Other   
OS: Other   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description Rosalie 2025-09-11 16:59:20 UTC 
SUMMARY
Hello, I've recently updated the com.github.Rosalie241.RMG flatpak's version to the latest released version, however it fails to launch and crashes deep within Qt:

https://github.com/flathub/com.github.Rosalie241.RMG/pull/98

```
(gdb) bt 
#0  0x00007ffff6011baf in QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::get (this=<optimized out>)
    at /run/build-runtime/qt6-qtbase/src/corelib/tools/qscopedpointer.h:112
#1  qGetPtrHelper<QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> > > (ptr=...)
    at /run/build-runtime/qt6-qtbase/src/corelib/global/qtclasshelpermacros.h:137
#2  QObject::d_func (this=<optimized out>) at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qobject.h:110
#3  QObjectPrivate::get (o=<optimized out>) at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qobject_p.h:151
#4  doActivate<false> (sender=0x0, signal_index=9, argv=0x7fffffffc170)
    at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qobject.cpp:4037
#5  0x00007ffff60085b7 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7ffff73dd760, 
    local_signal_index=local_signal_index@entry=1, argv=argv@entry=0x7fffffffc170)
    at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qobject.cpp:4217
#6  0x00007ffff6bf1584 in QMetaObject::activate<void, QScreen*> (sender=<optimized out>, mo=0x7ffff73dd760, 
    local_signal_index=1, ret=0x0) at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qobjectdefs.h:306
#7  QGuiApplication::screenAdded (this=<optimized out>, _t1=<optimized out>, _t1@entry=0x55555574cc20)
    at /run/build-runtime/qt6-qtbase/src/gui/Gui_autogen/include/moc_qguiapplication.cpp:300
#8  0x00007ffff6c753bd in QWindowSystemInterface::handleScreenAdded (platformScreen=platformScreen@entry=0x55555570e310, 
    isPrimary=<optimized out>) at /run/build-runtime/qt6-qtbase/src/gui/kernel/qwindowsysteminterface.cpp:730
#9  0x00007ffff45e3fc1 in QXcbConnection::initializeScreens (this=this@entry=0x55555571ffd0, 
    initialized=initialized@entry=false)
    at /run/build-runtime/qt6-qtbase/src/plugins/platforms/xcb/qxcbconnection_screens.cpp:313
#10 0x00007ffff45d9401 in QXcbConnection::QXcbConnection (this=0x55555571ffd0, nativeInterface=<optimized out>, 
    canGrabServer=false, defaultVisualId=<optimized out>, displayName=<optimized out>)
    at /run/build-runtime/qt6-qtbase/src/plugins/platforms/xcb/qxcbconnection.cpp:71
#11 0x00007ffff4601c60 in QXcbIntegration::QXcbIntegration (this=this@entry=0x555555718e20, parameters=..., 
    argc=@0x7fffffffccac: 1, argv=argv@entry=0x7fffffffd608)
    at /run/build-runtime/qt6-qtbase/src/corelib/tools/qscopedpointer.h:105
#12 0x00007ffff7faa519 in QXcbIntegrationPlugin::create (this=<optimized out>, system=..., parameters=..., 
    argc=@0x7fffffffccac: 1, argv=0x7fffffffd608)
    at /run/build-runtime/qt6-qtbase/src/plugins/platforms/xcb/qxcbmain.cpp:22
#13 0x00007ffff6bf7b11 in init_platform (pluginNamesWithArguments=..., platformPluginPath=..., platformThemeName=..., 
    argc=@0x7fffffffccac: 1, argv=argv@entry=0x7fffffffd608)
    at /run/build-runtime/qt6-qtbase/src/gui/kernel/qguiapplication.cpp:1309
#14 0x00007ffff6bfb368 in QGuiApplicationPrivate::createPlatformIntegration (this=0x555555707f50)
    at /run/build-runtime/qt6-qtbase/src/gui/kernel/qguiapplication.cpp:1591
#15 0x00007ffff6bfbf00 in QGuiApplicationPrivate::createEventDispatcher (this=<optimized out>)
    at /run/build-runtime/qt6-qtbase/src/gui/kernel/qguiapplication.cpp:1610
--Type <RET> for more, q to quit, c to continue without paging--
#16 0x00007ffff5faf875 in QCoreApplicationPrivate::init (this=this@entry=0x555555707f50)
    at /run/build-runtime/qt6-qtbase/src/corelib/kernel/qcoreapplication.cpp:866
#17 0x00007ffff6bff29d in QGuiApplicationPrivate::init (this=0x555555707f50)
    at /run/build-runtime/qt6-qtbase/src/gui/kernel/qguiapplication.cpp:1638
#18 0x00007ffff77a7925 in QApplicationPrivate::init (this=0x555555707f50)
    at /run/build-runtime/qt6-qtbase/src/widgets/kernel/qapplication.cpp:476
#19 0x00007ffff77a7a0d in QApplication::QApplication (this=<optimized out>, argc=<optimized out>, argv=<optimized out>)
    at /run/build-runtime/qt6-qtbase/src/widgets/kernel/qapplication.cpp:464
#20 0x000055555559f04d in main (argc=<optimized out>, argv=0x7fffffffd608) at /run/build/RMG/Source/RMG/main.cpp:182
```

I've tried reverting the version change but that crashes in the same way:
https://github.com/flathub/com.github.Rosalie241.RMG/pull/99

I've also tried downgrading the runtime version to 6.8 but that *also* has the same issue:
https://github.com/flathub/com.github.Rosalie241.RMG/pull/100


STEPS TO REPRODUCE
1. Try to compile a Qt app
2. it fails to launch
Comment 1 Albert Astals Cid 2025-09-11 18:35:11 UTC 
interestingly changing to -DCMAKE_BUILD_TYPE=Debug in your app seems to make it work, which potentially means the problem is in your app and not the runtime?
Comment 2 Rosalie 2025-09-11 19:14:53 UTC 
(In reply to Albert Astals Cid from comment #1)
> interestingly changing to -DCMAKE_BUILD_TYPE=Debug in your app seems to make
> it work, which potentially means the problem is in your app and not the
> runtime?

Thank you for looking into it, that pointed me in the right direction, disabling LTO fixes the crash.

I apologize for the noise and greatly appreciate your help, I had no idea LTO could cause such a strange crash seemingly in the Qt libraries but TIL!