[ros-dev] Re: [ros-diffs] [CVS reactos] - Saved the state of the fpu at a win32 call and restored the state

Gregor Anich blight at blight.eu.org
Sat Nov 27 22:57:25 CET 2004

Hi Hartmut!

You have changed the w32 callback to save the FPU state, this is wrong I 
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
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