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SSE instructions in DOS programs? (Developers)

posted by RayeR(R) Homepage, CZ, 03.01.2019, 14:32

I guess that SSE should work without setting those 2 bits in CR4 - if you don't need turn on exceptions (code should work without them too). I'm not sure what exactly bit 9 does. FXSAVE instruction save FPU, MMX, SSE regs. context to given location in memory. But as I told for a single task OS it's not necessary if no other code will use this regs. Here is better description with some sample code
https://wiki.osdev.org/SSE
they even set some bits in CR0.
In order to allow SSE instructions to be executed without generating a #UD, we need to alter the CR0 and CR4 registers.
I don't know what they means by "#UD" but from this description it seems that bits must be enabled to allow SSE instructions even on single task OS. But you told it didn't crash. I'm confused...

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DOS gives me freedom to unlimited HW access.

 

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