Garbage Collection (GC) in the Java Virtual Machine (JVM) serves as an automatic memory management mechanism, efficiently reclaiming unused memory space in different production scenarios. To optimize JVM performance, developers typically fine-tune the garbage collector by identifying an optimal set of GC configurations for specific scenarios. Despite the sophisticated design of garbage collectors, they still have the potential for bugs in different settings, and these bugs can result in more severe consequences. Hence, comprehensive testing of these garbage collectors is imperative before their release. Code coverage criteria are typically employed to assess the comprehensiveness of a test suite. However, traditional code coverage metrics, such as branch coverage, are hardly applicable for GC testing due to their inherent concurrency. Additionally, existing JVM testing techniques do not adequately consider the characteristics of garbage collectors, making it difficult to test these garbage collectors sufficiently. In this article, we make the first effort to design coverage criteria against garbage collectors based on the events of GC called Event-Coverage . Its key insight is to measure the diversity of GC executions for testing purposes by assessing the range of GC events these executions cover. Furthermore, we design a new testing method for maximizing Event-Coverage called GCFuzz . GCFuzz conducts an exhaustive investigation of the memory state space of GC and thoroughly explores the memory state under various GC configurations. To enhance GCFuzz’s efficiency in achieving higher Event-Coverage, we have further designed a coverage-driven strategy for preserving candidate seed programs and selecting GC configurations. Extensive evaluations demonstrate a positive correlation between Event-Coverage and the bug-revealing efficiency. Moreover, GCFuzz outperforms state-of-the-art techniques in detecting unique GC-related inconsistencies and achieving higher Event-Coverage. Remarkably, GCFuzz has identified 20 previously undetected GC bugs, with 15 of them already confirmed or fixed by developers.

JVM fuzzing techniques serve as a cornerstone for guaranteeing the quality of implementations. In typical fuzzing workflows, initial seeds are crucial as they form the basis of the process. Literature in traditional program fuzzing has confirmed that effectiveness is largely impacted by redundancy among initial seeds, thereby proposing a series of seed selection methods. JVM fuzzing, compared to traditional ones, presents unique characteristics, including large-scale and intricate code, and programs with both syntactic and semantic features. However, it remains unclear whether the existing initial seed selection methods are suitable for JVM fuzzing and whether utilizing program features can enhance effectiveness. To address this, we devise a total of 10 initial seed selection methods, comprising coverage-based, prefuzz-based, and program-feature-based methods. We then conduct an empirical study on three JVM implementations to extensively evaluate the performance of the initial seed selection methods within two state-of-the-art fuzzing techniques (JavaTailor and VECT). Specifically, we examine performance from three aspects: (i) effectiveness and efficiency using widely studied initial seeds, (ii) effectiveness using the programs in the wild, and (iii) the ability to detect new bugs. Evaluation results first show that the program-feature-based method that utilizes the control flow graph not only has a significantly lower time overhead (i.e., 30s), but also outperforms other methods, achieving 142% to 269% improvement compared to the full set of initial seeds. Second, results reveal that the initial seed selection greatly improves the quality of wild programs and exhibits complementary effectiveness by detecting new behaviors. Third, results demonstrate that given the same testing period, initial seed selection improves the JVM fuzzing techniques by detecting more unknown bugs. Particularly, 21 out of the 25 detected bugs have been confirmed or fixed by developers. This work takes the first look at initial seed selection in JVM fuzzing, confirming its importance in fuzzing effectiveness and efficiency.

Java Virtual Machine (JVM) holds a crucial position in executing various Java programs, thereby necessitating rigorous testing to ensure software reliability and security. Regarding existing JVM testing techniques, synthesis-based techniques have proven to be state-of-the-art, which construct a test program by synthesizing various program ingredients extracted from historical bug-revealing test programs into a seed program. However, existing synthesis-based techniques directly use the program ingredients specific to historical bugs, which limits the test scope without the ability of covering more JVM features and negatively affects the diversity of synthesized test programs.

JVM testing is one of the most widely-used methodologies for guaranteeing the quality of JVMs. Among various JVM testing techniques, synthesis-based JVM testing, which constructs a test program by synthesizing various code snippets (also called program ingredients), has been demonstrated state-of-the-art. The existing synthesis-based JVM testing work puts more efforts in ensuring the validity of synthesized test programs, but ignores the influence of huge ingredient space, which largely limits the ingredient exploration efficiency as well as JVM testing performance. In this work, we propose Vectorized JVM Testing (called VECT) to further promote the performance of synthesis-based JVM testing. Its key insight is to reduce the huge ingredient space by clustering semantically similar ingredients via vectorizing ingredients using state-of-the-art code representation. To make VECT complete and more effective, based on vectorized ingredients, VECT further designs a feedback-driven ingredient selection strategy and an enhanced test oracle. We conducted an extensive study to evaluate VECT on three popular JVMs (i.e., HotSpot, OpenJ9, and Bisheng JDK) involving five OpenJDK versions. The results demonstrate VECT detects 115.03% ~ 776.92% more unique inconsistencies than the state-of-the-art JVM testing technique during the same testing time. In particular, VECT detects 26 previously unknown bugs for them, 15 of which have already been confirmed/fixed by developers.

Copy-move forgery is the most predominant forgery technique in the field of digital image forgery. Block-based and interest-based are currently the two mainstream categories for copy-move forgery detection methods. However, block-based algorithm lacks the ability to resist affine transformation attacks, and interest point-based algorithm is limited to accurately locate the tampered region. To tackle these challenges, a coarse-to-fine model (CFM) is proposed. By extracting features, affine transformation matrix and detecting forgery regions, the localization of tampered areas from sparse to precise is realized. Specifically, in order to further exactly extract the forged regions and improve performance of the model, a two-level local search algorithm is designed in the refinement stage. In the first level, the image blocks are used as search units for feature matching, and the second level is to refine the edge of the region at pixel level. The method maintains a good balance between the complexity and effectiveness of forgery detection, and the experimental results show that it has a better detection effect than the traditional interest-based copy and move forgery detection method. In addition, CFM method has high robustness on postprocessing operations, such as scaling, rotation, noise, and JPEG compression.