KVM: x86 emulator: add CBW/CWDE/CDQE instruction emulation

index 46b7da8..1d36c38 100644
@@ -2290,7 +2290,7 @@ static struct opcode opcode_table[256] = {
 	/* 0x90 - 0x97 */
 	X8(D(SrcAcc | DstReg)),
 	/* 0x98 - 0x9F */
-	N, N, D(SrcImmFAddr | No64), N,
+	D(DstAcc | SrcNone), N, D(SrcImmFAddr | No64), N,
 	D(ImplicitOps | Stack), D(ImplicitOps | Stack), N, N,
 	/* 0xA0 - 0xA7 */
 	D(ByteOp | DstAcc | SrcMem | Mov | MemAbs), D(DstAcc | SrcMem | Mov | MemAbs),

@@ -3011,6 +3011,13 @@ special_insn:
 		if (c->dst.addr.reg == &c->regs[VCPU_REGS_RAX])
 			break;
 		goto xchg;
+	case 0x98: /* cbw/cwde/cdqe */
+		switch (c->op_bytes) {
+		case 2: c->dst.val = (s8)c->dst.val; break;
+		case 4: c->dst.val = (s16)c->dst.val; break;
+		case 8: c->dst.val = (s32)c->dst.val; break;
+		}
+		break;
 	case 0x9c: /* pushf */
 		c->src.val =  (unsigned long) ctxt->eflags;
 		emulate_push(ctxt, ops);

index bedd175..ce8fb18 100644
@@ -1236,6 +1236,32 @@ void test_loopcc(void)
 		print_serial("LOOPcc short Test 3: PASS\n");
 }
 
+void test_cbw(void)
+{
+	struct regs inregs = { 0 }, outregs;
+
+	MK_INSN(cbw, "mov $0xFE, %eax \n\t"
+		     "cbw\n\t");
+	MK_INSN(cwde, "mov $0xFFFE, %eax \n\t"
+		      "cwde\n\t");
+
+	exec_in_big_real_mode(&inregs, &outregs,
+			      insn_cbw,
+			      insn_cbw_end - insn_cbw);
+	if (outregs.eax != 0xFFFE)
+		print_serial("cbw test1: FAIL\n");
+	else
+		print_serial("cbw test 1: PASS\n");
+
+	exec_in_big_real_mode(&inregs, &outregs,
+			      insn_cwde,
+			      insn_cwde_end - insn_cwde);
+	if (outregs.eax != 0xFFFFFFFE)
+		print_serial("cwde test1: FAIL\n");
+	else
+		print_serial("cwde test 1: PASS\n");
+}
+
 void realmode_start(void)
 {
 	test_null();

@@ -1264,6 +1290,7 @@ void realmode_start(void)
 	test_div();
 	test_idiv();
 	test_loopcc();
+	test_cbw();
 
 	exit(0);
 }