Hi Hartmut!
You have changed the w32 callback to save the FPU state, this is wrong I think! I was wondering too wether it should be saved so GvG suggested to check myself and I modified our winhello app... It prints out the FPU control word, calls CreateWindow and printf the FPU control word again. In the callback for the WM_CREATE message (produced by CreateWindow) it also prints the control word, then modifies it (and prints the modified one)
This is the output on windows2000: Original FPU control word: 0x8001f WM_CREATE: Original FPU control word: 0x8001f WM_CREATE: Modified FPU control word: 0xa001f FPU control word after CreateWindow: 0xa001f
Of course I have attached the program.
I am not sure but I think in the KiClearFloatingPointState which you have added you have to set KPCR->NpxThread to NULL if it's CurrentThread before you do the fn/xsave because it could raise a delayed FPU exception (which will be ignored when KPCR->CurrentThread is NULL and be delivered when the saved FPU state is restored for the thread)
I think I have made the same mistake in tskswitch.S - I am pretty sure it has to be fixed there because we don't want a FPU exception to be raised while we are in a cli/sti block and switching to another task.
- blight