diff --git a/core/vm/plugin_hooks.go b/core/vm/plugin_hooks.go
new file mode 100644
index 000000000..728e3c75f
--- /dev/null
+++ b/core/vm/plugin_hooks.go
@@ -0,0 +1,5 @@
+package vm
+
+func (st *Stack) Len() int {
+	return len(st.data)
+}