From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <aliguori@us.ibm.com>
Subject: Re: [Patch 4/7] RealMode: Adds support for jmp far 0xea
Date: Tue, 27 May 2008 13:32:40 -0500
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References: <20080527084115.2b0cfae1@frecb000711.frec.bull.fr> <20080527101908.749cff41@frecb000711.frec.bull.fr>
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Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Avi Kivity <avi@qumranet.com>,
	Anthony Liguori <aliguori@linux.vnet.ibm.com>,
	Mohammed Gamal <m.gamal005@gmail.com>,
	"Kamble, Nitin A" <nitin.a.kamble@intel.com>,
	Marcelo Tosatti <mtosatti@redhat.com>, laurent.vivier@bull.net,
	Alexander Graf <alex@csgraf.de>
To: Guillaume Thouvenin <guillaume.thouvenin@ext.bull.net>
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Guillaume Thouvenin wrote:
>  Adds support for jmp far 0xea instruction
>
>
> Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@ext.bull.net>
> Signed-off-by: Laurent Vivier <laurent.vivier@bull.net>
>
> ---
>  arch/x86/kvm/x86_emulate.c |   31 +++++++++++++++++++++++++++++--
>  1 files changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
> index a928aa6..48b62cc 100644
> --- a/arch/x86/kvm/x86_emulate.c
> +++ b/arch/x86/kvm/x86_emulate.c
> @@ -168,7 +168,8 @@ static u16 opcode_table[256] = {
>  	/* 0xE0 - 0xE7 */
>  	0, 0, 0, 0, 0, 0, 0, 0,
>  	/* 0xE8 - 0xEF */
> -	ImplicitOps | Stack, SrcImm|ImplicitOps, 0, SrcImmByte|ImplicitOps,
> +	ImplicitOps | Stack, SrcImm | ImplicitOps,
> +	ImplicitOps, SrcImmByte | ImplicitOps,
>  	0, 0, 0, 0,
>  	/* 0xF0 - 0xF7 */
>  	0, 0, 0, 0,
> @@ -1661,7 +1662,33 @@ special_insn:
>  		break;
>  	}
>  	case 0xe9: /* jmp rel */
> -	case 0xeb: /* jmp rel short */
> +		goto jmp;
>   

The cases don't have to be in ascending order.  Much better to leave 
0xeb here then have a jmp cross case boundaries.

Regards,

Anthony Liguori

> +	case 0xea: /* jmp far */ {
> +		uint32_t eip;
> +		uint16_t sel;
> +
> +		switch (c->op_bytes) {
> +		case 2:
> +			eip = insn_fetch(u16, 2, c->eip);
> +			break;
> +		case 4:
> +			eip = insn_fetch(u32, 4, c->eip);
> +			break;
> +		default:
> +			DPRINTF("jmp far: Invalid op_bytes\n");
> +			goto cannot_emulate;
> +		}
> +		sel = insn_fetch(u16, 2, c->eip);
> +		if (kvm_load_segment_descriptor(ctxt->vcpu, sel, 9, VCPU_SREG_CS) < 0) {
> +			DPRINTF("jmp far: Failed to load CS descriptor\n");
> +			goto cannot_emulate;
> +		}
> +
> +		c->eip = eip;
> +		break;
> +	}
> +	case 0xeb:
> +	      jmp:		/* jmp rel short */
>  		jmp_rel(c, c->src.val);
>  		c->dst.type = OP_NONE; /* Disable writeback. */
>  		break;
>