This is certainly WinDbg 101 stuff, but the things I read in the Help file aren't sufficient.
1. Fired up WinDbg. Opened a window to local Kernel (File->Kernel Debug...->Local tab->OK).
2. ed Kd_IHVDRIVER_Mask, value is already 0xffffffff.
3. In the DriverEntry function, I call DbgPrintEx (DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, fmt, args...);
4. Start the driver using the SC START command.
5. Nothing in the WinDbg session window.
6. !dbgprint says the DbgPrint buffer is empty.
By the way, if I close the session window, File->Kernel Debug... remains grayed out, and I have to quit WinDbg and start it again if I want to repeat the above. What am I doing wrong here, and is this a clue regarding the missing debug output?
I have WinDbg 10.0.17763.1 AMD64, and Windows 10 OS 1803.