prevent multiple calls to LoadELF (#201)

* fixed state check in the LoadELF (avoid multiple loading)

* added a UT

* fixed UT

manager.go

@@ -430,7 +430,7 @@ func (m *Manager) GetProbe(id ProbeIdentificationPair) (*Probe, bool) {
 func (m *Manager) LoadELF(elf io.ReaderAt) error {
 	m.stateLock.Lock()
 	defer m.stateLock.Unlock()
-	if m.state > elfLoaded {
+	if m.state >= elfLoaded {
 		return ErrManagerELFLoaded
 	}
 	return m.loadELF(elf)

manager_test.go

@@ -261,3 +261,21 @@ func TestInstructionPatching(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestLoadELF(t *testing.T) {
+	f, err := os.Open("testdata/patching.elf")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = f.Close() })
+
+	m := &Manager{
+		state: reset,
+	}
+	if err = m.LoadELF(f); err != nil {
+		t.Errorf("LoadELF() error = %v, expected: %v", err, nil)
+	}
+	if err = m.LoadELF(f); !errors.Is(err, ErrManagerELFLoaded) {
+		t.Errorf("LoadELF() error = %v, expected: %v", err, ErrManagerELFLoaded)
+	}
+}