core/vm: implement RETURNDATA metropolis opcodes

core/vm/interpreter.go

@@ -60,6 +60,8 @@ type Interpreter struct {
 	intPool  *intPool
 
 	readonly bool
+	// returnData contains the last call's return data
+	returnData []byte
 }
 
 // NewInterpreter returns a new instance of the Interpreter.
@@ -113,6 +115,10 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret
 	in.evm.depth++
 	defer func() { in.evm.depth-- }()
 
+	// Reset the previous call's return data. It's unimportant to preserve the old buffer
+	// as every returning call will return new data anyway.
+	in.returnData = nil
+
 	// Don't bother with the execution if there's no code.
 	if len(contract.Code) == 0 {
 		return nil, nil
@@ -213,10 +219,10 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret
 		case !operation.jumps:
 			pc++
 		}
-		// if the operation returned a value make sure that is also set
-		// the last return data.
-		if res != nil {
-			mem.lastReturn = ret
+		// if the operation clears the return data (e.g. it has returning data)
+		// set the last return to the result of the operation.
+		if operation.clearsReturndata {
+			in.returnData = res
 		}
 	}
 	return nil, nil