[Interest] Crashes related to QAccessibleWidget on OSX

Adam Light aclight at gmail.com
Sun Jan 3 17:13:34 CET 2016


We've had a few crash reports from users of our application that seem to be
caused by QAccessibleWidget. I've experienced it myself once or twice as
well. In all cases it's happened on OSX, but some reports are on 10.10 and
some on 10.11.

We've seen the crash with both Qt 5.5.1 and 5.6 beta.

Here are a few examples of the call stack of the crashed thread.

0 org.qt-project.QtWidgets 0x06714dd0 QAccessibleWidget::state() const + 48
1 libqcocoa.dylib 0x09518baa 0x94dd000 + 244650
2 libqcocoa.dylib 0x095151e5 0x94dd000 + 229861
3 com.apple.AppKit 0x95a3d9bb
 _NSAccessibilityEntryPointIsAttributeSupported + 292
4 com.apple.AppKit 0x95a3d88f
 NSAccessibilityEntryPointIsAttributeSupported + 24
5 com.apple.AppKit 0x95a3d85b ValueOfAttributeWithDefault + 64

0 org.qt-project.QtWidgets     0x000000011428fc21 QAccessibleWidget::rect()
const + 33
1 org.qt-project.QtGui     0x0000000114685bf9
QAccessibleObject::childAt(int, int) const + 73
2 libqcocoa.dylib     0x0000000116d6a70d 0x116d33000 + 227085
3 com.apple.AppKit     0x00007fff9182f658 -[NSWindow(NSWindowAccessibility)
accessibilityHitTest:] + 508
4 com.apple.AppKit     0x00007fff91445219
-[NSApplication(NSApplicationAccessibility) accessibilityHitTest:] + 254
5 com.apple.AppKit     0x00007fff9142b223 CopyElementAtPosition + 313

0 org.qt-project.QtWidgets     0x066a2600 QAccessibleWidget::rect() const +
48
1 org.qt-project.QtGui     0x069e853f QAccessibleObject::childAt(int, int)
const + 63
2 libqcocoa.dylib     0x094d7ac0 0x949d000 + 240320
3 libqcocoa.dylib     0x094bd819 0x949d000 + 133145
4 com.apple.AppKit     0x9c86241a -[NSWindow(NSWindowAccessibility)
accessibilityHitTest:] + 572
5 com.apple.AppKit     0x9c45c297
-[NSApplication(NSApplicationAccessibility) accessibilityHitTest:] + 340
6 com.apple.AppKit     0x9c43d95e CopyElementAtPosition + 475

The rest of the call stack is mostly calls to system routines. Sometimes
there is some of our application's code much earlier in the call stack, and
sometimes there is nothing from our application other than the call to
main().

I haven't been able to figure out a way to reproduce this. I have tried
enabling voice over and the screen reader functionality provided by the
system in an attempt to provoke the crash, but I wasn't able to get the
crash by turning on those features. As far as I know, none of the users who
have run into this crash have any accessibility features turned on. I know
I don't (except in the case mentioned above when I turned them on to try to
provoke the crash).

I don't understand why there are no symbols given for the calls within
libqcocoa.dylib.

Does anyone have any suggestions for what I can do to figure out what is
causing the crash?

Thanks
Adam
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