Bug in libX11 or something near ?

Philippe philippe.raven@gmail.com
Tue Jun 18 16:08:00 GMT 2019

Hello Cygwin list !

I'm using Cygwin/X and identified a critical bug using some piece of
I don't really know where to begin, but I'm able to crash some applications
via the application's menu, only with Cygwin/X (no crash with Xming, and no
crash under any Linux distributions).

For information, It goes through VirtualGL. I'll give the example on how to
reproduce it with a free software : Paraview (under linux).

So you open Paraview, then clic on "View" > show the "Toolbars" submenu,
then you move your mouse directly on the "Sources" or "Edit" menu, then it
crashes immediately. The only error message in the linux shell (from where
it was launched) is "paraview: Fatal IO error: client killed".

I got those lines in the XWin.0.log file :
SetupSysMenu: GetSystemMenu() failed for HWND 0x130746
winTopLevelWindowProc - WM_DESTROY - WM_WM_KILL

I'm on the last available libX11, libxcb1 etc .

If you have any idea, thanks :)


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