Re: [Xen-devel] [PATCH 1/3] x86: add support for computing the instruction length

[Mihai DonÈu <mdontu@xxxxxxxxxxxxxxx>]

On Tue, 9 Sep 2014 11:47:05 +0300 Mihai DonÈu wrote:
> On Tuesday 09 September 2014 05:28:02 Mihai DonÈu wrote:
> > This patch adds support for computing the length of an instruction. The 
> > entire
> > logic relies on a set of opcode tables generated by gen-insn-attr-x86.awk 
> > from
> > x86-opcode-map.txt and a number of small helper functions. It originated in
> > Linux, where it was added by Masami Hiramatsu. Since it's an almost 
> > identical
> > copy, it's separated from the x86 emulator, simplifying future updates.
> > 
> > ---
> > Changed since v1:
> >   * adjusted the coding style to match the rest of xen
> >   * moved the source files into x86/x86_emulate
> >   * replaced inat-tables.c with x86-opcode-map.txt and gen-insn-attr-x86.awk
> >     that are used to generate it
> > 
> > Signed-off-by: Mihai DonÈu <mdontu@xxxxxxxxxxxxxxx>
> 
> There are a couple of design issues with this code which Jan pointed
> out and which I overlooked. I'm sorry, it was not intentional. I'll do
> my best to address them in a following email.

I'd like to give it a try at saving some time by asking the author
behind the Linux code what is his opinion on this.

Masami, I'm trying to bring to xen the code you wrote for Linux a while
back and which uses an opcode map, a script and some helper functions
(insn.c, inat.c) to compute an instruction's length. Jan has made some
observations which I believe would be of interest to the kernel
developers as well. Please see:

http://lists.xenproject.org/archives/html/xen-devel/2014-07/msg00375.html

While valid, would they affect the overall goal of insn_get_length() or
is that function tuned for a specific use case? I can't yet tell for
sure if we can get away with it.

Thanks,

-- 
Mihai DonÈu

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