Log-based anomaly detection has been widely studied and achieves a satisfying performance on stable log data. But, the existing approaches still fall short meeting these challenges: 1) Log formats are changing continually in practice in those software systems under active development and maintenance. 2) Performance issues are latent causes that may not be detected by trivial monitoring tools. We thus propose SwissLog, namely a robust and unified deep learning based anomaly detection model for detecting diverse faults. SwissLog targets at those faults resulting in log sequence order changes and log time interval changes. To achieve that, an advanced log parser is introduced. Moreover, the semantic embedding and the time embedding approaches are combined to train a unified attention based BiLSTM model to detect anomalies. The experiments on real-world datasets and synthetic datasets show that SwissLog is robust to the changing log data and effective for diverse faults.