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Date: Wed, 29 Jan 2014 19:13:59 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] pxe boot problems
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To: Laszlo Ersek <lersek@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Dietmar Maurer <dietmar@proxmox.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Il 29/01/2014 19:09, Laszlo Ersek ha scritto:
> Yes, but as far I can see, the commit (which is not in RHEL-6) changes
> *how* the operand of ljmp is decoded.
>
> From "opcode_table" in RHEL-6's "arch/x86/kvm/emulate.c":
>
>
>         /* 0xE8 - 0xEF */
>         SrcImm | Stack, SrcImm | ImplicitOps,
>         SrcImmU | Src2Imm16 | No64, SrcImmByte | ImplicitOps,
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> and the patch changes that to
>
>         SrcImmFAddr | No64
>
> and adds new logic to fetch this source operand type.
>
> ... Which then seems to have an effect on what goes into
> load_segment_descriptor() as segment selector, in the emulation of 0xea.
>
> Of course I'm insufficiently equipped to debate this with you in earnest
> :), but it seemed relevant to me.

Yeah, it seems relevant to me too.

But before it was decoding two immediates, one after another, the first 
c->op_bytes long in c->src, and the second 2 bytes long in c->src2.  Now 
it's doing the same, but putting all c->op_bytes+2 bytes in c->src...

Though I guess the backport should be relatively easy if you want to try.

Paolo