Use uint64 for block header timestamp

core/vm/environment.go

@@ -17,7 +17,7 @@ type Environment interface {
 	BlockNumber() *big.Int
 	GetHash(n uint64) common.Hash
 	Coinbase() common.Address
-	Time() int64
+	Time() uint64
 	Difficulty() *big.Int
 	GasLimit() *big.Int
 	Transfer(from, to Account, amount *big.Int) error

core/vm/vm.go

@@ -444,7 +444,7 @@ func (self *Vm) Run(context *Context, input []byte) (ret []byte, err error) {
 		case TIMESTAMP:
 			time := self.env.Time()
 
-			stack.push(big.NewInt(time))
+			stack.push(new(big.Int).SetUint64(time))
 
 		case NUMBER:
 			number := self.env.BlockNumber()