Code based adversarial attacks play a crucial role in revealing vulnerabilities of software system. Recently, pre-trained programming language models (PLMs) have demonstrated remarkable success in various significant software engineering tasks, progressively transforming the paradigm of software development. Despite their impressive capabilities, these powerful models are vulnerable to adversarial attacks. Therefore, it is necessary to carefully investigate the robustness and vulnerabilities of the PLMs by means of adversarial attacks. Adversarial attacks entail imperceptible input modifications that cause target models to make incorrect predictions. Existing approaches for attacking PLMs often employ either identifier renaming or the greedy algorithm, which may yield sub-optimal performance or lead to high inference times. In response to these limitations, we propose CARL, an unsupervised black-box attack model that leverages reinforcement learning to generate imperceptible adversarial examples. Specifically, CARL comprises a programming language encoder and a perturbation prediction layer. In order to achieve more effective and efficient attack, we cast the task as a sequence decision-making process, optimizing through policy gradient with a suite of reward functions. We conduct extensive experiments to validate the effectiveness of CARL on code summarization, code translation, and code refinement tasks, covering various programming languages and PLMs. The experimental results demonstrate that CARL surpasses state-of-the-art code attack models, achieving the highest attack success rate across multiple tasks and PLMs while maintaining high attack efficiency, imperceptibility, consistency, and fluency.

Vanilla image completion approaches exhibit sensitivity to large missing regions, attributed to the limited availability of reference information for plausible generation. To mitigate this, existing methods incorporate the extra cue as guidance for image completion. Despite improvements, these approaches are often restricted to employing a *single modality* (e.g., *segmentation* or *sketch* maps), which lacks scalability in leveraging multi-modality for more plausible completion. In this paper, we propose a novel, simple yet effective method for **M**ulti-mod**a**l **G**uided **I**mage **C**ompletion, dubbed **MaGIC**, which not only supports a wide range of single modality as the guidance (e.g., *text*, *canny edge*, *sketch*, *segmentation*, *depth*, and *pose*), but also adapts to arbitrarily customized combinations of these modalities (i.e., *arbitrary multi-modality*) for image completion. For building MaGIC, we first introduce a modality-specific conditional U-Net (MCU-Net) that injects single-modal signal into a U-Net denoiser for single-modal guided image completion. Then, we devise a consistent modality blending (CMB) method to leverage modality signals encoded in multiple learned MCU-Nets through gradient guidance in latent space. Our CMB is *training-free*, thereby avoiding the cumbersome joint re-training of different modalities, which is the secret of MaGIC to achieve exceptional flexibility in accommodating new modalities for completion. Experiments show the superiority of MaGIC over state-of-the-art methods and its generalization to various completion tasks.