Extract isCallTo into its own function

* Check that `len(args)` is greater than 4

core/vm/instructions.go

@@ -35,7 +35,7 @@ var (
 	tt255                    = math.BigPow(2, 255)
 	OvmSLOADMethodId         = crypto.Keccak256([]byte("ovmSLOAD()"))[0:4]
 	OvmSSTOREMethodId        = crypto.Keccak256([]byte("ovmSSTORE()"))[0:4]
-	OvmContractAddress       = common.FromHex(os.Getenv("EXECUTION_MANAGER_ADDRESS"))
+	OvmContractAddress       = common.HexToAddress(os.Getenv("EXECUTION_MANAGER_ADDRESS"))
 	errWriteProtection       = errors.New("evm: write protection")
 	errReturnDataOutOfBounds = errors.New("evm: return data out of bounds")
 	errExecutionReverted     = errors.New("evm: execution reverted")
@@ -762,16 +762,15 @@ func opCall(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory
 	value = math.U256(value)
 	// Get the arguments from the memory.
 	args := memory.GetPtr(inOffset.Int64(), inSize.Int64())
-	methodId := args[0:4]
 
-	if bytes.Equal(toAddr.Bytes(), OvmContractAddress) && bytes.Equal(methodId, OvmSLOADMethodId) {
+	if isCallTo(toAddr, args, OvmContractAddress, OvmSLOADMethodId) {
 		storageSlot := new(big.Int).SetBytes(args[4:36])
 		stack.push(storageSlot)
 		opSload(pc, interpreter, contract, memory, stack)
 		storageValue := stack.peek()
 		memory.Set(retOffset.Uint64(), retSize.Uint64(), storageValue.Bytes())
 		return storageValue.Bytes(), nil
-	} else if bytes.Equal(toAddr.Bytes(), OvmContractAddress) && bytes.Equal(methodId, OvmSSTOREMethodId) {
+	} else if isCallTo(toAddr, args, OvmContractAddress, OvmSSTOREMethodId) {
 		storageSlot := new(big.Int).SetBytes(args[4:36])
 		storageValue := new(big.Int).SetBytes(args[36:68])
 		stack.push(storageValue)
@@ -799,6 +798,14 @@ func opCall(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory
 	}
 }
 
+func isCallTo(addr common.Address, args []byte, testAddr common.Address, testMethodId []byte) bool {
+	if len(args) < 4 {
+		return false
+	}
+	methodId := args[0:4]
+	return addr == testAddr && bytes.Equal(methodId, testMethodId)
+}
+
 func opCallCode(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	// Pop gas. The actual gas is in interpreter.evm.callGasTemp.
 	interpreter.intPool.put(stack.pop())

tests/ovm_test.go

@@ -2,7 +2,6 @@ package tests
 
 import (
 	"bytes"
-	"fmt"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -27,7 +26,7 @@ func mstoreBytes(bytes []byte, offset int) []byte {
 	return output
 }
 
-func call(addr []byte, value uint, inOffset uint, inSize uint, retOffset uint, retSize uint) []byte {
+func call(addr common.Address, value uint, inOffset uint, inSize uint, retOffset uint, retSize uint) []byte {
 	output := []byte{
 		byte(vm.PUSH1), 0,
 		byte(vm.PUSH1), 0,
@@ -39,7 +38,7 @@ func call(addr []byte, value uint, inOffset uint, inSize uint, retOffset uint, r
 	}
 	output = append(output, []byte{
 		byte(vm.PUSH20)}...)
-	output = append(output, addr...)
+	output = append(output, addr.Bytes()...)
 	output = append(output, []byte{
 		byte(vm.GAS),
 		byte(vm.CALL),
@@ -48,7 +47,6 @@ func call(addr []byte, value uint, inOffset uint, inSize uint, retOffset uint, r
 }
 
 func TestOvm(t *testing.T) {
-	fmt.Printf("%x", vm.OvmSSTOREMethodId)
 	db := state.NewDatabase(rawdb.NewMemoryDatabase())
 	state, _ := state.New(common.Hash{}, db)
 	address := common.HexToAddress("0x0a")