Xen devel - Jul 2007 - [PATCH] add mov instruction decoder in protected to real mode in vmxassist

decode mov instruction in protected to real mode in vmxassist.
Also some clean up.

Signed-off-by: Xin Li <xin.b.li@intel.com>


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>>> "Li, Xin B" <xin.b.li@intel.com> 02.07.07 18:03
>>>
>decode mov instruction in protected to real mode in vmxassist.
>Also some clean up.
>
>Signed-off-by: Xin Li <xin.b.li@intel.com>
This is what I really don''t like about decoder adjustments: Even when
changes
for a certain instruction type are found necessary, no care is taken that
similar
instructions are also updated/added. In this case, for instance, you add the
register destination/source case for opcode 0x89/0x8B, but the same adjustments
aren''t made for opcode 0x88/0x8A. This is calling for future problems,
as much
as e.g. the absence of emulation of opcode 0xC7 despite present emulation
of 0xC6. I''m not going to continue, but I suppose you get my point.

Also, how come that the mode/address size conditions are different for
0x88/0x8A versus 0x89/0x8B (they were identical so far for 0x88, 0x8A, and
0x8B, with some extra code for 0x89)?

Jan


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>This is what I really don''t like about decoder adjustments: 
>Even when changes for a certain instruction type are found necessary,
no care is 
>taken that similar instructions are also updated/added. In this case,
for 
>instance, you add the register destination/source case for opcode
0x89/0x8B, but the 
>same adjustments aren''t made for opcode 0x88/0x8A. This is calling
for
future 
>problems, as much as e.g. the absence of emulation of opcode 0xC7
despite 
>present emulation of 0xC6. I''m not going to continue, but I suppose
you
get my point.

A complete, maybe perfect, decoder, that''s also my ultimate goal :-).
>
>Also, how come that the mode/address size conditions are different for
>0x88/0x8A versus 0x89/0x8B (they were identical so far for 0x88, 0x8A,
and
>0x8B, with some extra code for 0x89)?
I don''t expect 0x89/0x8B (movb) will be used in switching from
protected
mode to real mode.

Intel SDM says, once software changes CR0.PE, it should *immediately*
use a long jump instruction to finish the mode switching between
real-address mode and protected mode. But this is not strictly obeyed,
and this is why I added the mov decoder here.

I will prefer to keep the VMXAssist decoder relatively small.

-Xin

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