[PATCH] x86_emulate: Emulate nop and xchg reg,rax (0x90 - 0x97) instructions

[PATCH] x86_emulate: Emulate nop and xchg reg,rax (0x90 - 0x97) instructions

[Mohammed Gamal]

This patch fixes the previous nop patch and adds the xchg reg,rax
instruction opcodes.

Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
---
 arch/x86/kvm/x86_emulate.c |   21 ++++++++++++++++++---
 1 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index b90857c..490417a 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -140,9 +140,12 @@ static u16 opcode_table[256] = {
 	ByteOp | DstReg | SrcMem | ModRM | Mov, DstReg | SrcMem | ModRM | Mov,
 	DstMem | SrcReg | ModRM | Mov, ModRM | DstReg,
 	DstReg | SrcMem | ModRM | Mov, Group | Group1A,
-	/* 0x90 - 0x9F */
-	0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 0, 0, ImplicitOps | Stack, ImplicitOps | Stack, 0, 0,
+	/* 0x90 - 0x97 */
+	ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+	ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+	/* 0x98 - 0x9F */
+	0, 0, 0, 0,
+	ImplicitOps | Stack, ImplicitOps | Stack, 0, 0,
 	/* 0xA0 - 0xA7 */
 	ByteOp | DstReg | SrcMem | Mov | MemAbs, DstReg | SrcMem | Mov | MemAbs,
 	ByteOp | DstMem | SrcReg | Mov | MemAbs, DstMem | SrcReg | Mov | MemAbs,
@@ -1493,6 +1496,7 @@ special_insn:
 		emulate_2op_SrcV("test", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0x86 ... 0x87:	/* xchg */
+	xchg:
 		/* Write back the register source. */
 		switch (c->dst.bytes) {
 		case 1:
@@ -1560,6 +1564,17 @@ special_insn:
 		if (rc != 0)
 			goto done;
 		break;
+	case 0x90: /* nop / xchg r8,rax */
+		if(! (c->rex_prefix & 1) )
+			break;
+	case 0x91 ... 0x97: /* xchg reg,rax */
+		c->src.type = c->dst.type = OP_REG;
+		c->src.bytes = c->dst.bytes = c->op_bytes;
+		c->src.ptr = (unsigned long *) &c->regs[VCPU_REGS_RAX];
+		c->src.val = *(c->src.ptr);
+		c->dst.ptr = decode_register( (c->b & 7) | ((c->rex_prefix & 1) <<
3), c->regs, 0);
+		c->dst.val = *(c->dst.ptr);
+		goto xchg;		
 	case 0x9c: /* pushf */
 		c->src.val =  (unsigned long) ctxt->eflags;
 		emulate_push(ctxt);

Re: [PATCH] x86_emulate: Emulate nop and xchg reg,rax (0x90 - 0x97) instructions

[Avi Kivity]

Mohammed Gamal wrote:
> This patch fixes the previous nop patch and adds the xchg reg,rax
> instruction opcodes.
>
>   
> +	case 0x90: /* nop / xchg r8,rax */
> +		if(! (c->rex_prefix & 1) )
> +			break;

space after if.

> +		c->dst.ptr = decode_register( (c->b & 7) | ((c->rex_prefix & 1) <<
> 3), c->regs, 0);
> +		c->dst.val = *(c->dst.ptr);
> +		goto xchg;		
>   

You can have the destination autodecoded by using DstReg instead of 
ImplicitOps.  Otherwise, looks fine.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.