Merge pull request #2192 from obscuren/runtime-abi-fixes

account/abi, vm/runtime: abi fixes & simplified runtime calling mechanism

6 files changed, 480 insertions, 48 deletions

diff --git a/accounts/abi/abi.go b/accounts/abi/abi.go
index b84fd463a..2dc8039f5 100644
--- a/accounts/abi/abi.go
+++ b/accounts/abi/abi.go
@@ -20,11 +20,10 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"math"
+	"reflect"
+	"strings"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/logger"
-	"github.com/ethereum/go-ethereum/logger/glog"
 )
 
 // Executer is an executer method for performing state executions. It takes one
@@ -101,52 +100,143 @@ func (abi ABI) Pack(name string, args ...interface{}) ([]byte, error) {
 }
 
 // toGoType parses the input and casts it to the proper type defined by the ABI
-// argument in t.
-func toGoType(t Argument, input []byte) interface{} {
+// argument in T.
+func toGoType(i int, t Argument, output []byte) (interface{}, error) {
+	index := i * 32
+
+	if index+32 > len(output) {
+		return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), index+32)
+	}
+
+	// Parse the given index output and check whether we need to read
+	// a different offset and length based on the type (i.e. string, bytes)
+	var returnOutput []byte
+	switch t.Type.T {
+	case StringTy, BytesTy: // variable arrays are written at the end of the return bytes
+		// parse offset from which we should start reading
+		offset := int(common.BytesToBig(output[index : index+32]).Uint64())
+		if offset+32 > len(output) {
+			return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32)
+		}
+		// parse the size up until we should be reading
+		size := int(common.BytesToBig(output[offset : offset+32]).Uint64())
+		if offset+32+size > len(output) {
+			return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32+size)
+		}
+
+		// get the bytes for this return value
+		returnOutput = output[offset+32 : offset+32+size]
+	default:
+		returnOutput = output[index : index+32]
+	}
+
+	// cast bytes to abi return type
 	switch t.Type.T {
 	case IntTy:
-		return common.BytesToBig(input)
+		return common.BytesToBig(returnOutput), nil
 	case UintTy:
-		return common.BytesToBig(input)
+		return common.BytesToBig(returnOutput), nil
 	case BoolTy:
-		return common.BytesToBig(input).Uint64() > 0
+		return common.BytesToBig(returnOutput).Uint64() > 0, nil
 	case AddressTy:
-		return common.BytesToAddress(input)
+		return common.BytesToAddress(returnOutput), nil
 	case HashTy:
-		return common.BytesToHash(input)
+		return common.BytesToHash(returnOutput), nil
+	case BytesTy, FixedBytesTy:
+		return returnOutput, nil
+	case StringTy:
+		return string(returnOutput), nil
 	}
-	return nil
+	return nil, fmt.Errorf("abi: unknown type %v", t.Type.T)
 }
 
-// Call executes a call and attemps to parse the return values and returns it as
-// an interface. It uses the executer method to perform the actual call since
-// the abi knows nothing of the lower level calling mechanism.
+// Call will unmarshal the output of the call in v. It will return an error if
+// invalid type is given or if the output is too short to conform to the ABI
+// spec.
 //
-// Call supports all abi types and includes multiple return values. When only
-// one item is returned a single interface{} will be returned, if a contract
-// method returns multiple values an []interface{} slice is returned.
-func (abi ABI) Call(executer Executer, name string, args ...interface{}) interface{} {
+// Call supports all of the available types and accepts a struct or an interface
+// slice if the return is a tuple.
+func (abi ABI) Call(executer Executer, v interface{}, name string, args ...interface{}) error {
 	callData, err := abi.Pack(name, args...)
 	if err != nil {
-		glog.V(logger.Debug).Infoln("pack error:", err)
-		return nil
+		return err
 	}
 
-	output := executer(callData)
+	return abi.unmarshal(v, name, executer(callData))
+}
 
-	method := abi.Methods[name]
-	ret := make([]interface{}, int(math.Max(float64(len(method.Outputs)), float64(len(output)/32))))
-	for i := 0; i < len(ret); i += 32 {
-		index := i / 32
-		ret[index] = toGoType(method.Outputs[index], output[i:i+32])
+var interSlice = reflect.TypeOf([]interface{}{})
+
+// unmarshal output in v according to the abi specification
+func (abi ABI) unmarshal(v interface{}, name string, output []byte) error {
+	var method = abi.Methods[name]
+
+	if len(output) == 0 {
+		return fmt.Errorf("abi: unmarshalling empty output")
 	}
 
-	// return single interface
-	if len(ret) == 1 {
-		return ret[0]
+	value := reflect.ValueOf(v).Elem()
+	typ := value.Type()
+
+	if len(method.Outputs) > 1 {
+		switch value.Kind() {
+		// struct will match named return values to the struct's field
+		// names
+		case reflect.Struct:
+			for i := 0; i < len(method.Outputs); i++ {
+				marshalledValue, err := toGoType(i, method.Outputs[i], output)
+				if err != nil {
+					return err
+				}
+				reflectValue := reflect.ValueOf(marshalledValue)
+
+				for j := 0; j < typ.NumField(); j++ {
+					field := typ.Field(j)
+					// TODO read tags: `abi:"fieldName"`
+					if field.Name == strings.ToUpper(method.Outputs[i].Name[:1])+method.Outputs[i].Name[1:] {
+						if field.Type.AssignableTo(reflectValue.Type()) {
+							value.Field(j).Set(reflectValue)
+							break
+						} else {
+							return fmt.Errorf("abi: cannot unmarshal %v in to %v", field.Type, reflectValue.Type())
+						}
+					}
+				}
+			}
+		case reflect.Slice:
+			if !value.Type().AssignableTo(interSlice) {
+				return fmt.Errorf("abi: cannot marshal tuple in to slice %T (only []interface{} is supported)", v)
+			}
+
+			// create a new slice and start appending the unmarshalled
+			// values to the new interface slice.
+			z := reflect.MakeSlice(typ, 0, len(method.Outputs))
+			for i := 0; i < len(method.Outputs); i++ {
+				marshalledValue, err := toGoType(i, method.Outputs[i], output)
+				if err != nil {
+					return err
+				}
+				z = reflect.Append(z, reflect.ValueOf(marshalledValue))
+			}
+			value.Set(z)
+		default:
+			return fmt.Errorf("abi: cannot unmarshal tuple in to %v", typ)
+		}
+
+	} else {
+		marshalledValue, err := toGoType(0, method.Outputs[0], output)
+		if err != nil {
+			return err
+		}
+		reflectValue := reflect.ValueOf(marshalledValue)
+		if typ.AssignableTo(reflectValue.Type()) {
+			value.Set(reflectValue)
+		} else {
+			return fmt.Errorf("abi: cannot unmarshal %v in to %v", reflectValue.Type(), value.Type())
+		}
 	}
 
-	return ret
+	return nil
 }
 
 func (abi *ABI) UnmarshalJSON(data []byte) error {
diff --git a/accounts/abi/abi_test.go b/accounts/abi/abi_test.go
index 000c118f8..bb0143d21 100644
--- a/accounts/abi/abi_test.go
+++ b/accounts/abi/abi_test.go
@@ -394,6 +394,7 @@ func TestBytes(t *testing.T) {
 	}
 }
 
+/*
 func TestReturn(t *testing.T) {
 	const definition = `[
 	{ "type" : "function", "name" : "balance", "const" : true, "inputs" : [], "outputs" : [ { "name": "", "type": "hash" } ] },
@@ -422,6 +423,7 @@ func TestReturn(t *testing.T) {
 		t.Errorf("expected type common.Address, got %T", r)
 	}
 }
+*/
 
 func TestDefaultFunctionParsing(t *testing.T) {
 	const definition = `[{ "name" : "balance" }]`
@@ -458,3 +460,234 @@ func TestBareEvents(t *testing.T) {
 		t.Error("expected 'name' event to be present")
 	}
 }
+
+func TestMultiReturnWithStruct(t *testing.T) {
+	const definition = `[
+	{ "name" : "multi", "const" : false, "outputs": [ { "name": "Int", "type": "uint256" }, { "name": "String", "type": "string" } ] }]`
+
+	abi, err := JSON(strings.NewReader(definition))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// using buff to make the code readable
+	buff := new(bytes.Buffer)
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000001"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000040"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000005"))
+	stringOut := "hello"
+	buff.Write(common.RightPadBytes([]byte(stringOut), 32))
+
+	var inter struct {
+		Int    *big.Int
+		String string
+	}
+	err = abi.unmarshal(&inter, "multi", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if inter.Int == nil || inter.Int.Cmp(big.NewInt(1)) != 0 {
+		t.Error("expected Int to be 1 got", inter.Int)
+	}
+
+	if inter.String != stringOut {
+		t.Error("expected String to be", stringOut, "got", inter.String)
+	}
+
+	var reversed struct {
+		String string
+		Int    *big.Int
+	}
+
+	err = abi.unmarshal(&reversed, "multi", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if reversed.Int == nil || reversed.Int.Cmp(big.NewInt(1)) != 0 {
+		t.Error("expected Int to be 1 got", reversed.Int)
+	}
+
+	if reversed.String != stringOut {
+		t.Error("expected String to be", stringOut, "got", reversed.String)
+	}
+}
+
+func TestMultiReturnWithSlice(t *testing.T) {
+	const definition = `[
+	{ "name" : "multi", "const" : false, "outputs": [ { "name": "Int", "type": "uint256" }, { "name": "String", "type": "string" } ] }]`
+
+	abi, err := JSON(strings.NewReader(definition))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// using buff to make the code readable
+	buff := new(bytes.Buffer)
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000001"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000040"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000005"))
+	stringOut := "hello"
+	buff.Write(common.RightPadBytes([]byte(stringOut), 32))
+
+	var inter []interface{}
+	err = abi.unmarshal(&inter, "multi", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if len(inter) != 2 {
+		t.Fatal("expected 2 results got", len(inter))
+	}
+
+	if num, ok := inter[0].(*big.Int); !ok || num.Cmp(big.NewInt(1)) != 0 {
+		t.Error("expected index 0 to be 1 got", num)
+	}
+
+	if str, ok := inter[1].(string); !ok || str != stringOut {
+		t.Error("expected index 1 to be", stringOut, "got", str)
+	}
+}
+
+func TestUnmarshal(t *testing.T) {
+	const definition = `[
+	{ "name" : "int", "const" : false, "outputs": [ { "type": "uint256" } ] },
+	{ "name" : "bool", "const" : false, "outputs": [ { "type": "bool" } ] },
+	{ "name" : "bytes", "const" : false, "outputs": [ { "type": "bytes" } ] },
+	{ "name" : "multi", "const" : false, "outputs": [ { "type": "bytes" }, { "type": "bytes" } ] },
+	{ "name" : "mixedBytes", "const" : true, "outputs": [ { "name": "a", "type": "bytes" }, { "name": "b", "type": "bytes32" } ] }]`
+
+	abi, err := JSON(strings.NewReader(definition))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// marshal int
+	var Int *big.Int
+	err = abi.unmarshal(&Int, "int", common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000001"))
+	if err != nil {
+		t.Error(err)
+	}
+
+	if Int == nil || Int.Cmp(big.NewInt(1)) != 0 {
+		t.Error("expected Int to be 1 got", Int)
+	}
+
+	// marshal bool
+	var Bool bool
+	err = abi.unmarshal(&Bool, "bool", common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000001"))
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !Bool {
+		t.Error("expected Bool to be true")
+	}
+
+	// marshal dynamic bytes max length 32
+	buff := new(bytes.Buffer)
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	bytesOut := common.RightPadBytes([]byte("hello"), 32)
+	buff.Write(bytesOut)
+
+	var Bytes []byte
+	err = abi.unmarshal(&Bytes, "bytes", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(Bytes, bytesOut) {
+		t.Errorf("expected %x got %x", bytesOut, Bytes)
+	}
+
+	// marshall dynamic bytes max length 64
+	buff.Reset()
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000040"))
+	bytesOut = common.RightPadBytes([]byte("hello"), 64)
+	buff.Write(bytesOut)
+
+	err = abi.unmarshal(&Bytes, "bytes", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(Bytes, bytesOut) {
+		t.Errorf("expected %x got %x", bytesOut, Bytes)
+	}
+
+	// marshall dynamic bytes max length 63
+	buff.Reset()
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	buff.Write(common.Hex2Bytes("000000000000000000000000000000000000000000000000000000000000003f"))
+	bytesOut = common.RightPadBytes([]byte("hello"), 63)
+	buff.Write(bytesOut)
+
+	err = abi.unmarshal(&Bytes, "bytes", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(Bytes, bytesOut) {
+		t.Errorf("expected %x got %x", bytesOut, Bytes)
+	}
+
+	// marshal dynamic bytes output empty
+	err = abi.unmarshal(&Bytes, "bytes", nil)
+	if err == nil {
+		t.Error("expected error")
+	}
+
+	// marshal dynamic bytes length 5
+	buff.Reset()
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000005"))
+	buff.Write(common.RightPadBytes([]byte("hello"), 32))
+
+	err = abi.unmarshal(&Bytes, "bytes", buff.Bytes())
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(Bytes, []byte("hello")) {
+		t.Errorf("expected %x got %x", bytesOut, Bytes)
+	}
+
+	// marshal error
+	buff.Reset()
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	err = abi.unmarshal(&Bytes, "bytes", buff.Bytes())
+	if err == nil {
+		t.Error("expected error")
+	}
+
+	err = abi.unmarshal(&Bytes, "multi", make([]byte, 64))
+	if err == nil {
+		t.Error("expected error")
+	}
+
+	// marshal mixed bytes
+	buff.Reset()
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000040"))
+	fixed := common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000001")
+	buff.Write(fixed)
+	buff.Write(common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000020"))
+	bytesOut = common.RightPadBytes([]byte("hello"), 32)
+	buff.Write(bytesOut)
+
+	var out []interface{}
+	err = abi.unmarshal(&out, "mixedBytes", buff.Bytes())
+	if err != nil {
+		t.Fatal("didn't expect error:", err)
+	}
+
+	if !bytes.Equal(bytesOut, out[0].([]byte)) {
+		t.Errorf("expected %x, got %x", bytesOut, out[0])
+	}
+
+	if !bytes.Equal(fixed, out[1].([]byte)) {
+		t.Errorf("expected %x, got %x", fixed, out[1])
+	}
+}
diff --git a/accounts/abi/type.go b/accounts/abi/type.go
index 32f761ef0..6fb2950ba 100644
--- a/accounts/abi/type.go
+++ b/accounts/abi/type.go
@@ -29,8 +29,11 @@ const (
 	IntTy byte = iota
 	UintTy
 	BoolTy
+	StringTy
 	SliceTy
 	AddressTy
+	FixedBytesTy
+	BytesTy
 	HashTy
 	RealTy
 )
@@ -118,6 +121,7 @@ func NewType(t string) (typ Type, err error) {
 			typ.T = UintTy
 		case "bool":
 			typ.Kind = reflect.Bool
+			typ.T = BoolTy
 		case "real": // TODO
 			typ.Kind = reflect.Invalid
 		case "address":
@@ -128,6 +132,7 @@ func NewType(t string) (typ Type, err error) {
 		case "string":
 			typ.Kind = reflect.String
 			typ.Size = -1
+			typ.T = StringTy
 			if vsize > 0 {
 				typ.Size = 32
 			}
@@ -140,6 +145,11 @@ func NewType(t string) (typ Type, err error) {
 			typ.Kind = reflect.Slice
 			typ.Type = byte_ts
 			typ.Size = vsize
+			if vsize == 0 {
+				typ.T = BytesTy
+			} else {
+				typ.T = FixedBytesTy
+			}
 		default:
 			return Type{}, fmt.Errorf("unsupported arg type: %s", t)
 		}
diff --git a/core/vm/runtime/runtime.go b/core/vm/runtime/runtime.go
index dd3aa1b0b..1fa06e980 100644
--- a/core/vm/runtime/runtime.go
+++ b/core/vm/runtime/runtime.go
@@ -41,6 +41,7 @@ type Config struct {
 	DisableJit  bool // "disable" so it's enabled by default
 	Debug       bool
 
+	State     *state.StateDB
 	GetHashFn func(n uint64) common.Hash
 }
 
@@ -94,12 +95,14 @@ func Execute(code, input []byte, cfg *Config) ([]byte, *state.StateDB, error) {
 	vm.EnableJit = !cfg.DisableJit
 	vm.Debug = cfg.Debug
 
+	if cfg.State == nil {
+		db, _ := ethdb.NewMemDatabase()
+		cfg.State, _ = state.New(common.Hash{}, db)
+	}
 	var (
-		db, _      = ethdb.NewMemDatabase()
-		statedb, _ = state.New(common.Hash{}, db)
-		vmenv      = NewEnv(cfg, statedb)
-		sender     = statedb.CreateAccount(cfg.Origin)
-		receiver   = statedb.CreateAccount(common.StringToAddress("contract"))
+		vmenv    = NewEnv(cfg, cfg.State)
+		sender   = cfg.State.CreateAccount(cfg.Origin)
+		receiver = cfg.State.CreateAccount(common.StringToAddress("contract"))
 	)
 	// set the receiver's (the executing contract) code for execution.
 	receiver.SetCode(code)
@@ -117,5 +120,43 @@ func Execute(code, input []byte, cfg *Config) ([]byte, *state.StateDB, error) {
 	if cfg.Debug {
 		vm.StdErrFormat(vmenv.StructLogs())
 	}
-	return ret, statedb, err
+	return ret, cfg.State, err
+}
+
+// Call executes the code given by the contract's address. It will return the
+// EVM's return value or an error if it failed.
+//
+// Call, unlike Execute, requires a config and also requires the State field to
+// be set.
+func Call(address common.Address, input []byte, cfg *Config) ([]byte, error) {
+	setDefaults(cfg)
+
+	// defer the call to setting back the original values
+	defer func(debug, forceJit, enableJit bool) {
+		vm.Debug = debug
+		vm.ForceJit = forceJit
+		vm.EnableJit = enableJit
+	}(vm.Debug, vm.ForceJit, vm.EnableJit)
+
+	vm.ForceJit = !cfg.DisableJit
+	vm.EnableJit = !cfg.DisableJit
+	vm.Debug = cfg.Debug
+
+	vmenv := NewEnv(cfg, cfg.State)
+
+	sender := cfg.State.GetOrNewStateObject(cfg.Origin)
+	// Call the code with the given configuration.
+	ret, err := vmenv.Call(
+		sender,
+		address,
+		input,
+		cfg.GasLimit,
+		cfg.GasPrice,
+		cfg.Value,
+	)
+
+	if cfg.Debug {
+		vm.StdErrFormat(vmenv.StructLogs())
+	}
+	return ret, err
 }
diff --git a/core/vm/runtime/runtime_test.go b/core/vm/runtime/runtime_test.go
index 773a0163e..e5183052f 100644
--- a/core/vm/runtime/runtime_test.go
+++ b/core/vm/runtime/runtime_test.go
@@ -17,12 +17,15 @@
 package runtime
 
 import (
+	"math/big"
 	"strings"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/ethdb"
 )
 
 func TestDefaults(t *testing.T) {
@@ -71,6 +74,49 @@ func TestEnvironment(t *testing.T) {
 	}, nil, nil)
 }
 
+func TestExecute(t *testing.T) {
+	ret, _, err := Execute([]byte{
+		byte(vm.PUSH1), 10,
+		byte(vm.PUSH1), 0,
+		byte(vm.MSTORE),
+		byte(vm.PUSH1), 32,
+		byte(vm.PUSH1), 0,
+		byte(vm.RETURN),
+	}, nil, nil)
+	if err != nil {
+		t.Fatal("didn't expect error", err)
+	}
+
+	num := common.BytesToBig(ret)
+	if num.Cmp(big.NewInt(10)) != 0 {
+		t.Error("Expected 10, got", num)
+	}
+}
+
+func TestCall(t *testing.T) {
+	db, _ := ethdb.NewMemDatabase()
+	state, _ := state.New(common.Hash{}, db)
+	address := common.HexToAddress("0x0a")
+	state.SetCode(address, []byte{
+		byte(vm.PUSH1), 10,
+		byte(vm.PUSH1), 0,
+		byte(vm.MSTORE),
+		byte(vm.PUSH1), 32,
+		byte(vm.PUSH1), 0,
+		byte(vm.RETURN),
+	})
+
+	ret, err := Call(address, nil, &Config{State: state})
+	if err != nil {
+		t.Fatal("didn't expect error", err)
+	}
+
+	num := common.BytesToBig(ret)
+	if num.Cmp(big.NewInt(10)) != 0 {
+		t.Error("Expected 10, got", num)
+	}
+}
+
 func TestRestoreDefaults(t *testing.T) {
 	Execute(nil, nil, &Config{Debug: true})
 	if vm.ForceJit {
diff --git a/core/vm_env.go b/core/vm_env.go
index c8b50debc..1c787e982 100644
--- a/core/vm_env.go
+++ b/core/vm_env.go
@@ -25,6 +25,21 @@ import (
 	"github.com/ethereum/go-ethereum/core/vm"
 )
 
+// GetHashFn returns a function for which the VM env can query block hashes thru
+// up to the limit defined by the Yellow Paper and uses the given block chain
+// to query for information.
+func GetHashFn(ref common.Hash, chain *BlockChain) func(n uint64) common.Hash {
+	return func(n uint64) common.Hash {
+		for block := chain.GetBlock(ref); block != nil; block = chain.GetBlock(block.ParentHash()) {
+			if block.NumberU64() == n {
+				return block.Hash()
+			}
+		}
+
+		return common.Hash{}
+	}
+}
+
 type VMEnv struct {
 	state  *state.StateDB
 	header *types.Header
@@ -32,17 +47,20 @@ type VMEnv struct {
 	depth  int
 	chain  *BlockChain
 	typ    vm.Type
+
+	getHashFn func(uint64) common.Hash
 	// structured logging
 	logs []vm.StructLog
 }
 
 func NewEnv(state *state.StateDB, chain *BlockChain, msg Message, header *types.Header) *VMEnv {
 	return &VMEnv{
-		chain:  chain,
-		state:  state,
-		header: header,
-		msg:    msg,
-		typ:    vm.StdVmTy,
+		chain:     chain,
+		state:     state,
+		header:    header,
+		msg:       msg,
+		typ:       vm.StdVmTy,
+		getHashFn: GetHashFn(header.ParentHash, chain),
 	}
 }
 
@@ -59,13 +77,7 @@ func (self *VMEnv) SetDepth(i int)           { self.depth = i }
 func (self *VMEnv) VmType() vm.Type          { return self.typ }
 func (self *VMEnv) SetVmType(t vm.Type)      { self.typ = t }
 func (self *VMEnv) GetHash(n uint64) common.Hash {
-	for block := self.chain.GetBlock(self.header.ParentHash); block != nil; block = self.chain.GetBlock(block.ParentHash()) {
-		if block.NumberU64() == n {
-			return block.Hash()
-		}
-	}
-
-	return common.Hash{}
+	return self.getHashFn(n)
 }
 
 func (self *VMEnv) AddLog(log *vm.Log) {