Syntax Tree Research Articles

Learning and Fusing Multi-View Code Representations for Function Vulnerability Detection

The explosive growth of vulnerabilities poses a significant threat to the security of software systems. While various deep-learning-based vulnerability detection methods have emerged, they primarily rely on semantic features extracted from a single code representation structure, which limits their ability to detect vulnerabilities hidden deep within the code. To address this limitation, we propose S2FVD, short for Sequence and Structure Fusion-based Vulnerability Detector, which fuses vulnerability-indicative features learned from the multiple views of the code for more accurate vulnerability detection. Specifically, S2FVD employs either well-matched or carefully extended neural network models to extract vulnerability-indicative semantic features from the token sequence, attributed control flow graph (ACFG) and abstract syntax tree (AST) representations of a function, respectively. These features capture different perspectives of the code, which are then fused to enable S2FVD to accurately detect vulnerabilities that are well-hidden within a function. The experiments conducted on two large vulnerability datasets demonstrated the superior performance of S2FVD against state-of-the-art approaches, with its accuracy and F1 scores reaching 98.07% and 98.14% respectively in detecting the presence of vulnerabilities, and 97.93% and 97.94%, respectively, in pinpointing specific vulnerability types. Furthermore, with regard to the real-world dataset D2A, S2FVD achieved average performance gains of 6.86% and 14.84% in terms of accuracy and F1 metrics, respectively, over the state-of-the-art baselines. This ablation study also confirms the superiority of fusing the semantics implied in multiple distinct code views to further enhance vulnerability detection performance.

A quantum-like text representation based on syntax tree for fuzzy semantic analysis

To mine more semantic information between words, it is important to utilize the different semantic correlations between words. Focusing on the different degrees of modifying relations between words, this article provides a quantum-like text representation based on syntax tree for fuzzy semantic analysis. Firstly, a quantum-like text representation based on density matrix of individual words is generalized to represent the relationship of modification between words. Secondly, a fuzzy semantic membership function is constructed to discuss the different degrees of modifying relationships between words based on syntax tree. Thirdly, the tensor dot product is defined as the sentence semantic similarity by combining the operation rules of the tensor to effectively exploit the semantic information of all elements in the quantum-like sentence representation. Finally, extensive experiments on STS’12, STS’14, STS’15, STS’16 and SICK show that the provided model outperforms the baselines, especially for the data set containing multiple long-sentence pairs, which confirms there are fuzzy semantic associations between words.

An Abstract Syntax Tree based static fuzzing mutation for vulnerability evolution analysis

An Abstract Syntax Tree based static fuzzing mutation for vulnerability evolution analysis

Applying Coding Behavior Features to Student Plagiarism Detection on Programming Assignments

In programming education, the result of plagiarism detection is a crucial criterion for assessing whether or not students can pass course exams. Recently, the prevalent methods for detecting student plagiarism have been proposed by analyzing source code. These methods extract features (such as token, abstract syntax tree and control flow graph) from the source code, examine the similarity of codes using various similarity detection methods, and then perform plagiarism detection based on a predefined plagiarism threshold. However, these previous methods for plagiarism detection have some problems. First, they are less effective in detecting code modification related to structure. Second, they require a considerable number of training data, which demand high computing time and space. Third, they cannot determine whether students plagiarize in time. We propose a novel plagiarism detection method by analyzing the behavioral features of students during the coding process. Specifically, we extract five behavioral features based on students’ programming habits. Then, we use a feature ranking-based suspiciousness algorithm to obtain the possibility of student plagiarism. Based on our proposed method, we develop the Online Integrated Programming Platform. To evaluate the accuracy of our method, we conduct a series of experiments. Final experimental results indicate that our method achieves promising results with Accuracy, Precision, Recall and [Formula: see text] values of 0.95, 0.90, 0.95 and 0.92, respectively. Finally, we also analyze the correlation between whether students plagiarized and their regular and final grades, which can further verify the effectiveness of our proposed method.

Smart contract vulnerability detection based on a semantic code structure and a self-designed neural network

Smart contracts are riddled with vulnerabilities due to flaws in programming languages and the inexperience of developers, causing damage. Nonetheless, the current research on smart contract vulnerability detection is insufficient. In this study, we propose a novel approach, namely, Blass, based on a semantic code structure and a self-designed neural network. Blass constructs program slices with complete semantic structure information (CPSs) and uses an abstract syntax tree and a depth-first traversal algorithm to convert CPSs into code chains during the process of CPS vectorization, which increases its ability to express vulnerability features. Blass also uses a self-designed neural network, Bi-LSTM-Att, as the classification model, which introduces an attention mechanism to capture the key features of vulnerabilities and effectively achieve improved smart contract vulnerability detection performance. The CPSs and the Bi-LSTM-Att can improve the vulnerability detection effectiveness of Blass, and Blass can be applied to malicious contract detection with satisfactory precision, recall, and F1 values.

"A Multi-Pass Compiler with Code Optimized Abstract Syntax Tree"

"A Multi-Pass Compiler with Code Optimized Abstract Syntax Tree"

Learning a holistic and comprehensive code representation for code summarization

Code summarization is the task of describing the function of code snippets in natural language, which benefits program comprehension and boosts software productivity. Despite lots of effort made by previous studies, existing models are not comprehensive enough to represent code, and yet the literature does not consider to model source code with API usage from a holistic perspective. To this end, this paper proposes a novel multi-modal code summarization approach called HCCS (Learning a Holistic and Comprehensive code representation for Code Summarization). We first design a neural network based on the graph attention mechanism to encode API Context Graph (ACG), which highlights holistic information of source code. Then, a multi-modal framework with a tree encoder for Abstract Syntax Tree (AST) and a code encoder for code tokens is incorporated to learn a more comprehensive code representation. Afterwards, we propose a fusing layer to integrate the encodings, which are then passed to a joint-decoder to generate summaries. The experimental results show that HCCS achieves better performance than the state of the arts (i.e., HCCS scores 9.5% higher in terms of BLEU metric and 11.46% in terms of BERTScore). As a result, HCCS is an effective approach to generate high-quality summaries.

Storage State Analysis and Extraction of Ethereum Blockchain Smart Contracts

In migrating and upgrading an Ethereum smart contract, it is necessary to transfer both the code as well as the stored data. Various methods attempt to migrate or upgrade a smart contract, but they are mostly manual, error-prone, and applicable only before deployment. Further, they have challenges in extracting the storage state of complex mapping data structures along with their keys. In this work, we present Smartmuv as an automatic source-code-based static analysis tool to analyze and extract the state from the storage-trie of smart contracts. Based on the abstract syntax tree and the control flow graphs of the Solidity source code, the tool analyzes each state variable including mapping types along the inheritance hierarchy. It also provides the upgrade algorithm that initializes the extracted state in the constructor of new smart contract. Smartmuv safely approximates the origin of the keys used in the mapping to extract values and has been able to extract the mapping state of 23,673 smart contracts with 95.7% overall precision. Moreover, we also validate the Smartmuv’s extracted state with the third-party tool Etherscan.

SVScanner: Detecting smart contract vulnerabilities via deep semantic extraction

Blockchain is a significant advancement in technology recently, transforming the traditional centralized system into a decentralized one. Smart contracts, as one of the best applications of blockchain, show great potential in various fields, such as finance, supply chain, and the Internet of Things (IoT). As the world’s first blockchain platform to support turing complete smart contracts, Ethereum has become the most critical infrastructure for the digital world. However, with the vigorous development of smart contracts, malicious attacks against smart contracts have frequently occurred in recent years. The issue of smart contract security has attracted widespread attention due to the huge financial losses caused by smart contract vulnerabilities. Although researchers have made some progress in detecting smart contract vulnerabilities through symbolic execution and fuzzing-based methods, existing methods mainly rely on expert knowledge and hand-crafted features, leading to many detection errors. Even worse, existing methods take tens of seconds or even minutes to detect each smart contract on average, which is extremely time-consuming. In this work, we present SVScanner, the new method combining two features of heterogeneous patterns to detect smart contract vulnerabilities in the blockchain. Specifically, we first extract global semantic features from the sequence of contract code tokens. Then we further use the attention mechanism to capture deep structural semantics from the Abstract Syntax Tree (AST) of smart contracts. Finally, we combine these two features from different patterns and use a text convolutional neural network (TextCNN) to detect contract bugs. Experimental results show that SVScanner has the ability to detect vulnerabilities effectively in real-world smart contract datasets. SVScanner achieves a 7.33% improvement in accuracy compared with other traditional methods. Moreover, our method requires significantly less detection time.

LCVD: Loop-oriented code vulnerability detection via graph neural network

Due to the unique mechanism and complex structure, loops in programs can easily lead to various vulnerabilities such as dead loops, memory leaks, resource depletion, etc. Traditional approaches to loop-oriented program analysis (e.g. loop summarization) are costly with a high rate of false positives in complex software systems. To address the issues above, recent works have applied deep learning (DL) techniques to vulnerability detection. However, existing DL-based approaches mainly focused on the general characteristics of most vulnerabilities without considering the semantic information of specific vulnerabilities. As a typical structure in programs, loops are highly iterative with multi-paths. Currently, there is a lack of available approaches to represent loops, as well as useful methods to extract the implicit vulnerability patterns. Therefore, this paper introduces LCVD, an automated loop-oriented code vulnerability detection approach. LCVD represents the source code as the Loop-flow Abstract Syntax Tree (LFAST), which focuses on interleaving multi-paths around loop structures. Then a novel Loop-flow Graph Neural Network (LFGNN) is proposed to learn both the local and overall structure of loop-oriented vulnerabilities. The experimental results demonstrate that LCVD outperforms the three static analysis-based and four state-of-the-art DL-based vulnerability detection approaches across evaluation settings.

Smart contract vulnerability detection based on semantic graph and residual graph convolutional networks with edge attention

Smart contracts are becoming the forefront of blockchain technology, allowing the performance of credible transactions without third parties. However, smart contracts on blockchain are not immune to vulnerability exploitation and cannot be modified after being deployed on the blockchain. Therefore, it is imperative to assure the security of smart contracts via intelligent vulnerability detection tools with the exponential increase in the number of smart contracts. The remarkably developing deep learning technology provides a promising way to detect potential smart contract vulnerabilities. Nevertheless, existing deep learning-based approaches fail to effectively capture the rich syntax and semantic information embedded in smart contracts for vulnerability detection. In this paper, we tackle the problem of smart contract vulnerability detection at the function level by constructing a novel semantic graph (SG) for each function and learning the SGs using graph convolutional networks (GCNs) with residual blocks and edge attention. Our proposed method consists of three stages. In the first stage, we create the SG which contains rich syntax and semantic information including the data–data, instruction–instruction and instruction–data relationships, variables, operations, etc., by building an abstract syntax tree (AST) from the code of each function, removing the unimportant nodes in the AST, and adding edges between the nodes to represent the data flows and the execution sequence of the statements. In the second stage, we propose a new graph convolutional network model EA-RGCN to learn the content and semantic features of the code. EA-RGCN contains three parts: node and edge representation via word2vec, content feature extraction with a residual GCN (RGCN) module, and semantic feature extraction using an edge attention (EA) module. In the third stage, we concatenate the code content features and the semantic features to obtain the global code feature and use a classifier to identify whether the function is vulnerable. We conduct experiments on the datasets constructed from real-world smart contracts. Experimental results demonstrate that the proposed semantic graph and the EA-RGCN model can effectively improve the performance in terms of accuracy, precision, recall, and F1-score on smart contract vulnerability detection.

Languages with Decidable Learning: A Meta-theorem

We study expression learning problems with syntactic restrictions and introduce the class of finite-aspect checkable languages to characterize symbolic languages that admit decidable learning. The semantics of such languages can be defined using a bounded amount of auxiliary information that is independent of expression size but depends on a fixed structure over which evaluation occurs. We introduce a generic programming language for writing programs that evaluate expression syntax trees, and we give a meta-theorem that connects such programs for finite-aspect checkable languages to finite tree automata, which allows us to derive new decidable learning results and decision procedures for several expression learning problems by writing programs in the programming language.

A Hierarchical Feature Ensemble Deep Learning Approach for Software Defect Prediction

Software defect prediction can detect modules that may have defects in advance and optimize resource allocation to improve test efficiency and reduce development costs. Traditional features cannot capture deep semantic and grammatical information, which limits the further development of software defect prediction. Therefore, it has gradually become a trend to use deep learning technology to automatically learn valuable deep features from source code or relevant data. However, most software defect prediction methods based on deep learning extraction features from a single information source or only use a single deep learning model, which leads to the fact that the extracted features are not comprehensive enough to affect the final prediction performance. In view of this, this paper proposes a Hierarchical Feature Ensemble Deep Learning (HFEDL) Approach for software defect prediction. Firstly, the HFEDL approach needs to obtain three types of information sources: abstract syntax tree (AST), class dependency network (CDN) and traditional features. Then, the Convolutional Neural Network (CNN) and the Bidirectional Long Short-Term Memory based on Attention mechanism (BiLSTM+Attention) are used to extract different valuable features from the three information sources and multiple prediction sub-models are constructed. Next, all the extracted features are fused by a filter mechanism to obtain more comprehensive features and construct a fusion prediction sub-model. Finally, all the sub-models are integrated by an ensemble learning method to obtain the final prediction model. We use 11 projects in the PROMISE defect repository and evaluate our approach in both non-effort-aware and effort-aware scenarios. The experimental results show that the prediction performance of our approach is superior to state-of-the-art methods in both scenarios.

Ideograph: A Language for Expressing and Manipulating Structured Data

We introduce Ideograph, a language for expressing and manipulating structured data. Its types describe kinds of structures, such as natural numbers, lists, multisets, binary trees, syntax trees with variable binding, directed multigraphs, and relational databases. Fully normalized terms of a type correspond exactly to members of the structure, analogous to a Church-encoding. Moreover, definable operations over these structures are guaranteed to respect the structures' equivalences. In this paper, we give the syntax and semantics of the non-polymorphic subset of Ideograph, and we demonstrate how it can represent and manipulate several interesting structures.

Predictive Comment Updating With Heuristics and AST-Path-Based Neural Learning: A Two-Phase Approach

Just-in-time comment update is a promising way to reduce the burden of developers during software maintenance and evolution. Existing approaches can be divided into two categories: the heuristic-based approach and the deep-learning-based approach. The heuristic-based approach is restricted to a specific type of comment updates (i.e., code-indicative updates), but performs well on such type. The effectiveness of deep-learning-based approach is limited but it can handle diverse comment updates. Considering the complementary advantages of existing approaches, an intuitive idea is to combine them for better performance. To investigate this idea, we first conduct a pre-study experiment which shows that to construct an effective comment updater by combining heuristic-based and deep-learning-based approaches, we need to tackle two main challenges: 1) the heuristic-based approach may bring side effects to cases which cannot be updated by it; and 2) the current deep-learning-based approach is with limited effectiveness. Then, we propose a novel two-phase approach named Toper to cope with these two challenges and effectively perform comment updates. In the first phase, Toper integrates nine distinctive features identified through our large-scale empirical analysis into a predictive model, which can predict whether the contents of the comment updates can be found in the corresponding code changes, namely, the comment updates are code-indicative updates. If so, the updates are then generated by an off-the-shelf heuristic-based approach; otherwise, Toper leverages a deep learning model, which we specially designed for non-code-indicative updates, to infer the new comment based on the old comment and code change. Motivated by our manual observation on the limitation of existing approaches on non-code-indicative updates, our deep learning model adopts the Abstract Syntax Tree path technique, which can capture the program structure information for effectively embedding code changes. Our evaluation shows that our approach outperforms the state-of-the-art by around 20% with respect to the number of correct comments it generates. Via in-depth analysis, we illustrate the rationale of each design decision as well as point out potential directions.

Three Approaches for Detecting Direct Output Cheating in Program Online Judge Systems

Program online judge (POJ) systems allow students to view questions, submit solution code, and receive scores automatically via the web. Most POJs use test cases for scoring. When a POJ is scored by test case pass rate or a problem that has only one test case, students can usually score by providing the direct output of the test cases (direct output cheating). Currently, there is only one work on detecting such cheating. However, its precision is very low. To solve this problem, three novel approaches are proposed to detect direct output cheating: (i) Line Statistics, which computes the proportion of output calls against other statements; (ii) the control flow graph (CFG) Search computes the maximum similarity between the CFG of a program and that of known samples; (iii) abstract syntax tree (AST) Search identifies cheating by matching rules that are summarized from ASTs of previously detected cheating attempts. A student’s code is marked as cheating if the similarity exceeds a predefined threshold; and a program is detected as cheating if the proportion exceeds a predefined threshold. The proposed approaches and three well-known code plagiarism detection tools (JPlag, Sherlock, and SIM) were evaluated using 100,000 submissions for 1153 problems from a POJ based on the C programming language. The F1 scores of these approaches were determined as 0.9752 (AST Search), 0.9440 (CFG Search), 0.7405 (Line Statistics), 0.6446 (JPlag), 0.1587 (Sherlock), and 0.0076 (SIM), respectively. The result indicates that (i) AST Search is most suitable for the detection of direct output cheating; (ii) traditional code search or plagiarism detection methods based on similarity calculations are not effective for complex cheat detection because these cheats are highly similar to normal code.

DeGraphCS : Embedding Variable-based Flow Graph for Neural Code Search

With the rapid increase of public code repositories, developers maintain a great desire to retrieve precise code snippets by using natural language. Despite existing deep learning-based approaches that provide end-to-end solutions (i.e., accept natural language as queries and show related code fragments), the performance of code search in the large-scale repositories is still low in accuracy because of the code representation (e.g., AST) and modeling (e.g., directly fusing features in the attention stage). In this paper, we propose a novel learnable de ep G raph for C ode S earch (called deGraphCS ) to transfer source code into variable-based flow graphs based on an intermediate representation technique, which can model code semantics more precisely than directly processing the code as text or using the syntax tree representation. Furthermore, we propose a graph optimization mechanism to refine the code representation and apply an improved gated graph neural network to model variable-based flow graphs. To evaluate the effectiveness of deGraphCS , we collect a large-scale dataset from GitHub containing 41,152 code snippets written in the C language and reproduce several typical deep code search methods for comparison. The experimental results show that deGraphCS can achieve state-of-the-art performance and accurately retrieve code snippets satisfying the needs of the users.

Towards Learning Generalizable Code Embeddings Using Task-agnostic Graph Convolutional Networks

Code embeddings have seen increasing applications in software engineering (SE) research and practice recently. Despite the advances in embedding techniques applied in SE research, one of the main challenges is their generalizability. A recent study finds that code embeddings may not be readily leveraged for the downstream tasks that the embeddings are not particularly trained for. Therefore, in this article, we propose GraphCodeVec , which represents the source code as graphs and leverages the Graph Convolutional Networks to learn more generalizable code embeddings in a task-agnostic manner. The edges in the graph representation are automatically constructed from the paths in the abstract syntax trees, and the nodes from the tokens in the source code. To evaluate the effectiveness of GraphCodeVec , we consider three downstream benchmark tasks (i.e., code comment generation, code authorship identification, and code clones detection) that are used in a prior benchmarking of code embeddings and add three new downstream tasks (i.e., source code classification, logging statements prediction, and software defect prediction), resulting in a total of six downstream tasks that are considered in our evaluation. For each downstream task, we apply the embeddings learned by GraphCodeVec and the embeddings learned from four baseline approaches and compare their respective performance. We find that GraphCodeVec outperforms all the baselines in five out of the six downstream tasks, and its performance is relatively stable across different tasks and datasets. In addition, we perform ablation experiments to understand the impacts of the training context (i.e., the graph context extracted from the abstract syntax trees) and the training model (i.e., the Graph Convolutional Networks) on the effectiveness of the generated embeddings. The results show that both the graph context and the Graph Convolutional Networks can benefit GraphCodeVec in producing high-quality embeddings for the downstream tasks, while the improvement by Graph Convolutional Networks is more robust across different downstream tasks and datasets. Our findings suggest that future research and practice may consider using graph-based deep learning methods to capture the structural information of the source code for SE tasks.

Improving Code Completion by Solving Data Inconsistencies in the Source Code with a Hierarchical Language Model

In the field of software engineering, applying language models to the token sequence of source code is the state-of-the-art approach to building a code recommendation system. When applying language models to source code, it is difficult for state-of-the-art language models to deal with the data inconsistency problem, which is caused by the free naming conventions of source code. It is common for user-defined variables or methods with similar semantics in source code, to have different names in different projects. This means that a model trained on one project may encounter many words the model has never seen before during another project. Those freely named variables or functions in the code will bring difficulties to the processes of training and prediction and cause a data inconsistency problem between projects. However, we discover that the syntax tree of source code has hierarchical structures. This code structure has strong regularity in different projects and can be used to combat data inconsistency. In this paper, we propose a novel Hierarchical Language Model (HLM) to improve the robustness of the state-of-the-art recurrent language model, in order to be able to deal with data inconsistency between training and testing. The newly proposed HLM takes the hierarchical structure of the code tree into consideration to predict code. The proposed HLM method generates the embedding for each sub-tree according to hierarchies and collects the embedding of each sub-tree in context, to predict the next piece of code. The experiments on inner-project and cross-project datasets indicate that the newly proposed HLM method performs better than the state-of-the-art recurrent language model in dealing with the data inconsistency between training and testing, and achieves an average improvement in prediction accuracy of 11.2%.

Structure and Sequence Aligned Code Summarization with Prefix and Suffix Balanced Strategy

Source code summarization focuses on generating qualified natural language descriptions of a code snippet (e.g., functionality, usage and version). In an actual development environment, descriptions of the code are missing or not consistent with the code due to human factors, which makes it difficult for developers to comprehend and conduct subsequent maintenance. Some existing methods generate summaries from the sequence information of code without considering the structural information. Recently, researchers have adopted the Graph Neural Networks (GNNs) to capture the structural information with modified Abstract Syntax Trees (ASTs) to comprehensively represent a source code, but the alignment method of the two information encoder is hard to decide. In this paper, we propose a source code summarization model named SSCS, a unified transformer-based encoder-decoder architecture, for capturing structural and sequence information. SSCS is designed upon a structure-induced transformer with three main novel improvements. SSCS captures the structural information in a multi-scale aspect with an adapted fusion strategy and adopts a hierarchical encoding strategy to capture the textual information from the perspective of the document. Moreover, SSCS utilizes a bidirectional decoder which generates a summary from opposite direction to balance the generation performance between prefix and suffix. We conduct experiments on two public Java and Python datasets to evaluate our method and the result show that SSCS outperforms the state-of-art code summarization methods.