KVM: x86 emulator: Add DstAcc operand type

Add DstAcc operand type. That means that there are 4 bits now for
DstMask.

"In the good old days cpus would have only one register that was able to
 fully participate in arithmetic operations, typically called A for
 Accumulator.  The x86 retains this tradition by having special, shorter
 encodings for the A register (like the cmp opcode), and even some
 instructions that only operate on A (like mul).

 SrcAcc and DstAcc would accommodate these instructions by decoding A
 into the corresponding 'struct operand'."
  -- Avi Kivity
Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@ext.bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/x86_emulate.c

@@ -47,25 +47,26 @@
 #define ImplicitOps (1<<1)	/* Implicit in opcode. No generic decode. */
 #define DstReg      (2<<1)	/* Register operand. */
 #define DstMem      (3<<1)	/* Memory operand. */
-#define DstMask     (3<<1)
+#define DstAcc      (4<<1)      /* Destination Accumulator */
+#define DstMask     (7<<1)
 /* Source operand type. */
-#define SrcNone     (0<<3)	/* No source operand. */
-#define SrcImplicit (0<<3)	/* Source operand is implicit in the opcode. */
-#define SrcReg      (1<<3)	/* Register operand. */
-#define SrcMem      (2<<3)	/* Memory operand. */
-#define SrcMem16    (3<<3)	/* Memory operand (16-bit). */
-#define SrcMem32    (4<<3)	/* Memory operand (32-bit). */
-#define SrcImm      (5<<3)	/* Immediate operand. */
-#define SrcImmByte  (6<<3)	/* 8-bit sign-extended immediate operand. */
-#define SrcMask     (7<<3)
+#define SrcNone     (0<<4)	/* No source operand. */
+#define SrcImplicit (0<<4)	/* Source operand is implicit in the opcode. */
+#define SrcReg      (1<<4)	/* Register operand. */
+#define SrcMem      (2<<4)	/* Memory operand. */
+#define SrcMem16    (3<<4)	/* Memory operand (16-bit). */
+#define SrcMem32    (4<<4)	/* Memory operand (32-bit). */
+#define SrcImm      (5<<4)	/* Immediate operand. */
+#define SrcImmByte  (6<<4)	/* 8-bit sign-extended immediate operand. */
+#define SrcMask     (7<<4)
 /* Generic ModRM decode. */
-#define ModRM       (1<<6)
+#define ModRM       (1<<7)
 /* Destination is only written; never read. */
-#define Mov         (1<<7)
-#define BitOp       (1<<8)
-#define MemAbs      (1<<9)      /* Memory operand is absolute displacement */
-#define String      (1<<10)     /* String instruction (rep capable) */
-#define Stack       (1<<11)     /* Stack instruction (push/pop) */
+#define Mov         (1<<8)
+#define BitOp       (1<<9)
+#define MemAbs      (1<<10)      /* Memory operand is absolute displacement */
+#define String      (1<<12)     /* String instruction (rep capable) */
+#define Stack       (1<<13)     /* Stack instruction (push/pop) */
 #define Group       (1<<14)     /* Bits 3:5 of modrm byte extend opcode */
 #define GroupDual   (1<<15)     /* Alternate decoding of mod == 3 */
 #define GroupMask   0xff        /* Group number stored in bits 0:7 */
@@ -1060,6 +1061,23 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 		}
 		c->dst.type = OP_MEM;
 		break;
+	case DstAcc:
+		c->dst.type = OP_REG;
+		c->dst.bytes = c->op_bytes;
+		c->dst.ptr = &c->regs[VCPU_REGS_RAX];
+		switch (c->op_bytes) {
+			case 1:
+				c->dst.val = *(u8 *)c->dst.ptr;
+				break;
+			case 2:
+				c->dst.val = *(u16 *)c->dst.ptr;
+				break;
+			case 4:
+				c->dst.val = *(u32 *)c->dst.ptr;
+				break;
+		}
+		c->dst.orig_val = c->dst.val;
+		break;
 	}
 
 	if (c->rip_relative)