segmentation fault triggered in QKeyMapper::changeKeyboard()

Marc_Van_Daele

From time to time, we get a segfault with a stacktrace similar to the one at the end of this message.
All stacktraces seem to originate in QKeyMapper::changeKeyboard().
The lower stack frames and the actual widget (QLineEdit in the example) differ between crashes.

We are using PyQt (Qt4.8.2 and sip 4.13.3).
We noted that, from Qt5.0.0 onwards, a large part of this QKeyMapper::changeKeyboard() function was commented out: an extra #if 0 was added as can be seen in the code snippet below

void QKeyMapper::changeKeyboard()
{
    instance()->d_func()->clearMappings();

    // ## TODO: Support KeyboardLayoutChange on QPA
#if 0
    // inform all toplevel widgets of the change
    QEvent e(QEvent::KeyboardLayoutChange);
    QWidgetList list = QApplication::topLevelWidgets();
    for (int i = 0; i < list.size(); ++i) {
	        QWidget *w = list.at(i);
	        qt_sendSpontaneousEvent(w, &e);
    }
#endif
}

Any ideas

why this extra #if 0 was added in Qt5
whether it is safe to also add this in (a local build of) Qt4.8
what this code was supposed to do in the first place?

Thanks in advance,

Marc
PS: Below is an example of the stacktraces we get

#0  0x00007fe60a5d8f6b in raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:42
#1  <signal handler called>
#2  sip_api_is_py_method (gil=0x7fff73c87d1c, pymc=0xfff3d8e "", sipSelf=0xfd54200, cname=0x0, mname=0x7fe5f1222ce4 "changeEvent")
    at /build/buildd-sip4_4.13.3-2-amd64-4XEr_m/sip4-4.13.3/siplib/siplib.c:7573
#3  0x00007fe5f10300a9 in sipQLineEdit::changeEvent (this=0xfff3d50, a0=0x7fff73c88490) at sipQtGuipart5.cpp:43517
#4  0x00007fe5f02211dc in QWidget::event (this=0xfff3d50, event=0x7fff73c88490) at kernel/qwidget.cpp:8752
#5  0x00007fe5f05d9ac7 in QLineEdit::event (this=0xfff3d50, e=0x7fff73c88490) at widgets/qlineedit.cpp:1524
#6  0x00007fe5f107466b in event (a0=0x7fff73c88490, this=0xfff3d50) at sipQtGuipart5.cpp:43589
#7  sipQLineEdit::event (this=0xfff3d50, a0=0x7fff73c88490) at sipQtGuipart5.cpp:43581
#8  0x00007fe5f01d170c in QApplicationPrivate::notify_helper (this=this@entry=0x7ddafe0, receiver=receiver@entry=0xfff3d50, e=e@entry=0x7fff73c88490) at kernel/qapplication.cpp:4556
#9  0x00007fe5f01d5b8a in QApplication::notify (this=0x7ffedb0, receiver=0xfff3d50, e=0x7fff73c88490) at kernel/qapplication.cpp:4417
#10 0x00007fe5f11fdc66 in notify (a1=0x7fff73c88490, a0=0xfff3d50, this=0x7ffedb0) at sipQtGuipart9.cpp:35916
#11 sipQApplication::notify (this=0x7ffedb0, a0=0xfff3d50, a1=0x7fff73c88490) at sipQtGuipart9.cpp:35908
#12 0x00007fe608dc5b5e in QCoreApplication::notifyInternal (this=0x7ffedb0, receiver=0xfff3d50, event=0x7fff73c88490) at kernel/qcoreapplication.cpp:915
#13 0x00007fe5f02271c4 in QKeyMapper::changeKeyboard () at kernel/qkeymapper.cpp:99
#14 0x00007fe5f024c3cd in QApplication::x11ProcessEvent (this=0x7ffedb0, event=0x7fff73c88a00) at kernel/qapplication_x11.cpp:3365

VRonin

can you show the content of sipQLineEdit::changeEvent?

Marc_Van_Daele

In the PyQt 4.9.4 code downoaded from https://sourceforge.net/projects/pyqt/files/PyQt4/ I find
(Note that we are using 4.9.3 but I couldn't find the sources of that version)

void sipQLineEdit::changeEvent(QEvent *a0)
{
    sip_gilstate_t sipGILState;
    PyObject *sipMeth;

    sipMeth = sipIsPyMethod(&sipGILState,&sipPyMethods[14],sipPySelf,NULL,sipName_changeEvent);

    if (!sipMeth)
    {
        QLineEdit::changeEvent(a0);
        return;
    }

    typedef void (*sipVH_QtCore_17)(sip_gilstate_t,PyObject *,QEvent *);

    ((sipVH_QtCore_17)(sipModuleAPI_QtGui_QtCore->em_virthandlers[17]))(sipGILState,sipMeth,a0);
}