[1/3] KVM: x86 emulator: fix negative bit offset BitOp instruction emulation

Commit Message

Wei Yongjun Aug. 6, 2010, 7:17 a.m. UTC

None

Patch

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0e360c6..470c7eb 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -724,6 +724,30 @@  done:
 	return rc;
 }
 
+static void fetch_bit_operand(struct decode_cache *c)
+{
+	unsigned long mask, byte_offset;
+
+	if (c->dst.type == OP_MEM) {
+		if (c->src.bytes == 2)
+			c->src.val = (s16)c->src.val;
+		else if (c->src.bytes == 4)
+			c->src.val = (s32)c->src.val;
+
+		mask = ~(c->dst.bytes * 8 - 1);
+
+		if ((long)c->src.val < 0) {
+			/* negative bit offset */
+			byte_offset = c->dst.bytes +
+				      ((-c->src.val - 1) & mask) / 8;
+			c->dst.addr.mem -= byte_offset;
+		} else {
+			/* positive bit offset */
+			c->dst.addr.mem += (c->src.val & mask) / 8;
+		}
+	}
+}
+
 static int read_emulated(struct x86_emulate_ctxt *ctxt,
 			 struct x86_emulate_ops *ops,
 			 unsigned long addr, void *dest, unsigned size)
@@ -2646,12 +2670,8 @@  done_prefixes:
 			c->dst.bytes = 8;
 		else
 			c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
-		if (c->dst.type == OP_MEM && (c->d & BitOp)) {
-			unsigned long mask = ~(c->dst.bytes * 8 - 1);
-
-			c->dst.addr.mem = c->dst.addr.mem +
-						   (c->src.val & mask) / 8;
-		}
+		if (c->d & BitOp)
+			fetch_bit_operand(c);
 		c->dst.orig_val = c->dst.val;
 		break;
 	case DstAcc: