core/vm: use methods over direct access to stack internals

core/vm/gas_table.go

@@ -345,7 +345,7 @@ func gasCreate2Eip3860(evm *EVM, contract *Contract, stack *Stack, mem *Memory,
 }
 
 func gasExpFrontier(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
-	expByteLen := uint64((stack.data[stack.len()-2].BitLen() + 7) / 8)
+	expByteLen := uint64((stack.Back(1).BitLen() + 7) / 8)
 
 	var (
 		gas      = expByteLen * params.ExpByteFrontier // no overflow check required. Max is 256 * ExpByte gas
@@ -358,7 +358,7 @@ func gasExpFrontier(evm *EVM, contract *Contract, stack *Stack, mem *Memory, mem
 }
 
 func gasExpEIP158(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
-	expByteLen := uint64((stack.data[stack.len()-2].BitLen() + 7) / 8)
+	expByteLen := uint64((stack.Back(1).BitLen() + 7) / 8)
 
 	var (
 		gas      = expByteLen * params.ExpByteEIP158 // no overflow check required. Max is 256 * ExpByte gas

core/vm/instructions_test.go

@@ -118,8 +118,8 @@ func testTwoOperandOp(t *testing.T, tests []TwoOperandTestcase, opFn executionFu
 		stack.push(x)
 		stack.push(y)
 		opFn(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
-		if len(stack.data) != 1 {
-			t.Errorf("Expected one item on stack after %v, got %d: ", name, len(stack.data))
+		if stack.len() != 1 {
+			t.Errorf("Expected one item on stack after %v, got %d: ", name, stack.len())
 		}
 		actual := stack.pop()
 
@@ -735,8 +735,8 @@ func TestRandom(t *testing.T) {
 			evmInterpreter = env.interpreter
 		)
 		opRandom(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
-		if len(stack.data) != 1 {
-			t.Errorf("Expected one item on stack after %v, got %d: ", tt.name, len(stack.data))
+		if have, want := stack.len(), 1; have != want {
+			t.Errorf("test '%v': want %d item(s) on stack, have %d: ", tt.name, have, want)
 		}
 		actual := stack.pop()
 		expected, overflow := uint256.FromBig(new(big.Int).SetBytes(tt.random.Bytes()))
@@ -777,8 +777,8 @@ func TestBlobHash(t *testing.T) {
 		)
 		stack.push(uint256.NewInt(tt.idx))
 		opBlobHash(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
-		if len(stack.data) != 1 {
-			t.Errorf("Expected one item on stack after %v, got %d: ", tt.name, len(stack.data))
+		if have, want := stack.len(), 1; have != want {
+			t.Errorf("test '%v': want %d item(s) on stack, have %d: ", tt.name, have, want)
 		}
 		actual := stack.pop()
 		expected, overflow := uint256.FromBig(new(big.Int).SetBytes(tt.expect.Bytes()))