linux-kernel - Re: AMD Geode i686

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Message-ID: <73c1f2161003011543q41197be9vbc79e0c86753f0d4@mail.gmail.com>
Date:	Mon, 1 Mar 2010 18:43:48 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Matteo Croce <technoboy85@...il.com>
Cc:	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: AMD Geode i686

On Mon, Mar 1, 2010 at 5:03 PM, Matteo Croce <technoboy85@...il.com> wrote:
> Hi,
> I have refreshed my AMD Geode i686 patch with NOPL and I have added a
> new nice feature.
> When a NOPL is found the parser looks for any NOPL after the current
> one, so they are emulated in bulk.
> Tested ok on a Pcengines Alix.
>
> Signed-off-by: Matteo Croce <technoboy85@...il.com>

1. Since this can possibly touch userspace, you must use get_user() to
read the instruction bytes.

2. This parser is too simple to cover all the possible encodings, not
just the recommended ones from the Intel manual.  You really should be
decoding:
- all prefixes (like segment overrides), which can be repeated.
- the 0f 1f opcode.
- the Mod R/M byte.
- the SIB byte (if present).
- the displacement.

This should probably be part of a more general instruction emulator.

--
Brian Gerst
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