:[diStorm}: problem decoding fnstsw

[Gil Dabah]

There are a few decoding for this instruction.
The constant 0xdf, 0xe0 which results in fnstsw ax (according to the AMD
specs it's AX, 16 bits operation).
And 0xdd, <modrm byte /7> which results in FNSTSW rm16.
But the modrm byte value must be lower than 0xC0, because that instruction
supports only memory indirection operand.

Maybe I should indeed put the AX in the operands string rather than the
mnemonic string itself.
I have never considered this before. If that might help you, I am willing to
do so.

On 2/13/07, Sanjay Patel <sanjay3000 at yahoo.com> wrote:
>
> I think this 2 byte sequence should be "fnstsw eax":
>
> 0xdf, 0xe0
>
> But diStorm seems to be returning "fnstsw ax" all in the mnemonic string
> rather than putting 'ax' into the operand string. My reading of the
> manuals
> is not very good - the modrm byte is specified as /7 - so does that mean
> that
> 0xe0 is invalid in this case?
>
> --Sanjay
>
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