Determining the cause of AccessViolationException DragDrop.DoDragDrop

Question

I have a WPF application that is crashing on some computers with an AccessViolationException when a drag operation is started.

The difficulty is it is only occurring on builds from our build server, and never crashes when I build locally in Visual Studio 2010. So I cannot step through the code.

I have the following information:

• We're using .net 4.0
• Only crashes when the application is run as a 64bit process, 32bit is fine.
• Only crashes for builds from the build server.
• Doesn't crash on every computer, just on a small subset of laptops we have here. Which incidentally are all the same model and hardware configuration. All have Windows 7, and some have sp1, some don't.

What is the next step I should take to diagnose this issue?

Here's the stack trace from the crash, it seems to be occurring in unmanaged code:

at MS.Win32.UnsafeNativeMethods.DoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
at System.Windows.OleServicesContext.OleDoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
at System.Windows.DragDrop.OleDoDragDrop(DependencyObject dragSource, DataObject dataObject, DragDropEffects allowedEffects)
at Acquire.Common.UI.Behaviours.DragDropBehaviour.StartDrag(RoutedEventArgs e)
at Acquire.Common.UI.Behaviours.DragDropBehaviour.AttachedElementMouseMove(Object sender, MouseEventArgs e)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
at System.Windows.Application.RunInternal(Window window)
at System.Windows.Application.Run()
at Acquire.Mica.Application.App.Main()

Update: Through trial and error I was able to determine the exact line of code that was causing this crash, and it appears to be perfectly valid. As an experiment I disabled code optimization for the method containing the offending line of code, and the application no longer crashes.

Answer 1

AV exception are the worst, you should be aware that the problem may originate from completely different part in the system.

What normally happens is that you accidently access a memory location that you don't have access to, the program continues to execute as usual, however later on another method tries to access that memory location and causes an error by reading incorrect data place there by mistake.

To debug I suggest that you take advantage of gflags, a tool offered by Microsoft to detect deap corruptions. I used it several times and it saved me hours if not days of debugging effort.