Re: [PATCH] [RFC] More fp instructions for realmode emulation (Enables booting OS/2 as a HVM guest on Intel/VT hardware)

[Keir Fraser <keir.fraser@eu.citrix.com>]

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Annoying fact #2 about the FPU instructions is that the GNU assembler
reverses the operand order of many two-operand FPU instructions. So, for
example, FDIVP becomes DIVRP, and vice versa. Super annoying. So I¹m going
to change our emulated opcodes for most FPU instructions to be ³.byte
xx,yy². Personally I think this is as clear as using the mnemonic opcode, or
perhaps clearer since it is now obvious that we are executing the exact
instruction that we have just decoded.

 -- Keir

On 29/2/08 22:14, "Trolle Selander" <trolle.selander@gmail.com> wrote:

> This patch adds a number of fp instructions needed for OS/2 to boot as a HVM
> guest on Intel/VT hardware. It appears to work fine, and OS/2 is now finally
> working on Intel/VT as well as AMD/SVM.
> 
> I'm a little concerned about the "correctness" of the FSTSW emulation and the
> use of inline assembly directly using the corresponding ops for emulation. Wrt
> FSTSW, it is really two ops FNSTSW immediately preceeded by an FWAIT. I've
> left FWAIT defined, but a no-op because after looking at realmode.c it seems
> in the emulation, exceptions are always processed if a call to x86_emulate
> returns an exception, so there should be no way for there to be "pending"
> exceptions for FWAIT to wait for. I may have missed something, though, hence
> the RFC.
> 
> Secondly, about the inline assembly - i saw that this was how many of the
> other FP instructions were done, so I did it that way as well. However, none
> of the previous instructions done that way referenced the fp registers. Does
> this make a difference, or is it ok the way i've done it here?
> 
> Signed-off-by: Trolle Selander <trolle.selander@gmail.com>
> 
> 
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