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Re: [Qemu-devel] [PATCH] multi-bytes nop and 64bits

From: malc
Subject: Re: [Qemu-devel] [PATCH] multi-bytes nop and 64bits
Date: Wed, 22 Apr 2009 02:30:35 +0400 (MSD)

On Tue, 21 Apr 2009, Mark Karpeles wrote:

> Le mardi 21 avril 2009 ЪЪ 21:20 +0400, malc a ЪЪcrit :
> > > Patch:
> > > http://ookoo.org/svn/snip/qemu-0.10.1-nopl-fix.patch
> > 
> > I'm not intimately familiar with binutils' disasm but it looks correct
> > save for the fact that hint_nop take M and not Ev as operand, which
> > might be irrelevant for disassembler though...
> To tell you the truth, I had a look at the current (ie. gdb 6.8) gdb
> disassembler, and saw it was "Ev". It also produces correct result when
> I look at the disassembled code (while the operand is irrelevant, it
> gives a hint regarding the whole opcode's size).
> I believe those who knows best how this decompiler works are those who
> have continued to improve it, so I didn't look too deep in this, just
> backported support for multibyte nop to code used in qemu (tried to port
> the whole decompiler, but it changed too much, and I'm too lazy to
> attempt to fix that).

Sandpile also states that hint_nop's take Ev 

That said this particular instance (0f 1f) should be covered by the code
that is currently in HEAD, strangely enough all other hint_nops and
prefetches are not. FWIW your patch seems wrong in prefetch[nta|t0]

> I'm just adding [PATCH] to the subject, just to let everyone here know
> this mail contains a patch. I successfully tested it on 3 machines
> without problems and it already saved my day once by showing me where my
> kernel was stopping (I'm in the process of porting from 32bits to
> 64bits, knowing what happens inside is a great help).
> Anyway the decompiler obviously needs to be either re-made, or
> re-imported from gdb, but this little patch will help until someone with
> better knowledge of qemu and gdb does it.

Licensing issues prevents us from doing so, the disassembler was hand
picked by Blue Swirl to the latest version released under GPL2.


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