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Regular Property Guided Dynamic Symbolic Execution Regular Property Guided Dynamic Symbolic Execution Yufeng Zhang∗y, Zhenbang Chenyx, Ji Wang∗y, Wei Dongy and Zhiming Liuz ∗State Key Laboratory of High Performance Computing, National University of Defense Technology, Changsha, China yCollege of Computer, National University of Defense Technology, Changsha, China zCentre for Software Engineering, Birmingham City University, Birmingham, UK Email: fyufengzhang, zbchen, wj, [email protected], [email protected] xCorresponding author Abstract—A challenging problem in software engineering is to Furthermore, techniques pursuing coverage, such as automatic check if a program has an execution path satisfying a regular test generation [10], are difficult to scale up. property. We propose a novel method of dynamic symbolic Dynamic symbolic execution (DSE) [11], [12] enhances execution (DSE) to automatically find a path of a program satisfying a regular property. What makes our method distinct traditional symbolic execution [13] by combing concrete ex- is when exploring the path space, DSE is guided by the synergy ecution and symbolic execution. DSE repeatedly runs the of static analysis and dynamic analysis to find a target path as program both concretely and symbolically. After each run, soon as possible. We have implemented our guided DSE method all the branches off the execution path, called the off-path- for Java programs based on JPF and WALA, and applied it branches, are collected, and then one of them is selected to 13 real-world open source Java programs, a total of 225K lines of code, for extensive experiments. The results show the to generate new inputs for the next run to explore a new effectiveness, efficiency, feasibility and scalability of the method. path. Hence, DSE improves the coverage through symbolic Compared with the pure DSE on the time to find the first target execution, and avoids false alarms by actually running the path, the average speedup of the guided DSE is more than 258X program. More importantly, DSE can use information of the when analyzing the programs that have more than 100 paths. concrete execution to simplify symbolic reasoning and handle environment modeling. I. INTRODUCTION When DSE is applied to checking a program against a regular property, an execution path satisfies the property if A regular property of a program can be represented by a the sequence of the events in the path is accepted by the Finite State Machine (FSM). The FSM is an abstract model FSM of the property, and we call this path an accepted path. of the executions of the program. A label (or event) of However, the number of paths is exponential with the number a transition corresponds to the execution of one or more of branch statements executed during DSE, which brings the statements in the program relevant to the property. FSM can path explosion problem. Therefore, how to guide DSE to find describe many kinds of program properties including resource a path satisfying the regular property as soon as possible is a usage (e.g., file usage [1]), memory safety (e.g., memory leak challenging problem. [2]), communication protocol [3], etc. In software engineering, We propose a novel DSE approach, called regular property regular properties and FSMs are widely used in different tech- guided DSE, to find the program paths satisfying a regular niques, such as model-based testing [4], typestate analysis [5], property as soon as possible. Our approach is based on the key and specification mining and synthesis [6]. These techniques insight that only the paths with specific sequences of events encounter the common problem of checking whether there can satisfy the regular property. The portion of the accepted exists a path of a program that satisfies a regular property. paths is often very small. It is desirable not to explore the Therefore, finding effective solutions to this problem and their irrelevant paths (i.e., the paths not containing any event in implementations are essential to many applications. the FSM) and the relevant paths not satisfying the property. Static analysis and dynamic analysis are the two effec- However, it is impossible to avoid all these paths. What we tive approaches used for checking regular properties. Static propose is to explore the off-path-branches along which the analysis, e.g., [7], [1], [5], usually enjoys the advantage of paths are most likely to satisfy the property. high coverage and good scalability. But its users are often The novelty of the guided DSE is the design of the algorithm bothered by false alarms, due to the extra behaviors introduced to evaluate the possibility of an off-path-branch along which by over approximation. The dynamic approach [8], [9] has there exists an accepted path. To this end, the evaluation uses the advantage of no false alarm, and can provide precise the history and future behaviors of the off-path-branch. For an information (such as the input) for replay. However, it is off-path-branch b, the history of b is described by the states confined by the problem of limited input coverage as only of the FSM that the current execution path has reached up to the program executions of the selected inputs can be checked. b. The future of b is described by the states of the FSM from For example, traditional software testing [4] has low coverage. which the final state can be reached by the execution of the program after b. We calculate the history in the DSE process 1 int foo(int m, int n, int tag) {//{ q0} and the future statically using backward dataflow analysis. If 2 File file = new File("...");//{ q0} 3 InputStreamReader w = new InputStreamReader( the intersection of the history and future of b is not empty, new FileInputStream(file));//{ q1; q2; q3} there is likely a path along b satisfying the regular property. 4 int result = 0;//{ q1; q2; q3} 5 int k = 0;//{ q1; q2; q3} We have implemented the guided DSE for Java programs, 6 while (k++ < m)//{ q1; q2; q3} based on JPF-JDart [14] and WALA [15]. The tool is applied 7 {//{ q1; q2; q3} 8 int i = w.read();//{ q1; q2; q3} to analyze 13 real-world open source Java programs, a total of 9 if (i == -1) break;//{q1; q2; q3} 225K lines of code, against representative regular properties. 10 result += i;//{ q1; q2; q3} 11 }//{ q1; q2; q3} The experimental results indicate that the guided DSE is more 12 if (tag == 0)//{ q1; q2; q3} efficient than the pure DSE with a lower time overhead and 13 {//{ q1; q2; q3} 14 w.close();//{ q2; q3} an acceptable memory overhead. 15 }//{ q2; q3} The main contributions of this paper are as follows: 16 k = 0;//{ q2; q3} 17 while (k++ < n)//{ q2; q3} • The algorithm for guiding DSE with respect to regular 18 {//{ q2; q3} properties: with the synergy of static analysis and dy- 19 int i = w.read();//{ q2; q3} 20 if (i == -1) break;//{q2; q3} namic analysis, the algorithm can find the program paths 21 result -= i;//{ q2; q3} satisfying a regular property effectively and efficiently. 22 }//{ q3} 23 return result; • The prototype tool of the guided DSE for Java programs: 24 } it is applied successfully to analyze 13 real-world Java Fig. 1. An example program programs with respect to regular properties. read • Extensive experiments: the results show that the guided read close DSE has 1) an average >1880X speedup on the iterations init close read needed to find the first accepted path, and 2) an average start q0 q1 q2 q3 >258X time speedup for finding the first accepted path on the programs whose path space is bigger than 100. Furthermore, for 3 out of the 13 programs, guided DSE Fig. 2. The FSM specifying the bug close successfully finds an accepted path in one hour, repro- ducing a known typestate bug; whereas, the pure DSE fails for these 3 programs in 24 hours. i i init st1 The rest of this paper is as follows. Section II motivates Preset:{q1} rread c1:m>0 our approach. Section III elaborates the details. Section IV b1 r presents the implementation and evaluation. We discuss related st 1 …...Postset:{q1,q2,q3} work in Section V, and conclusion in Section VI. Preset:{q1} c2:m<=1 b2 II. MOTIVATING EXAMPLE st2 … Postset:{q1,q2,q3} Preset:{q1} ... To motivate the guided DSE, Fig. 1 shows a program that c3:tag!=0 b3 selected in regular uses an InputStreamReader to read a file. Procedure foo property guided DSE st 3 …Postset... :{q1,q2,q3} has three integer parameters and two loops in lines 6−11 and Preset:{q1} c :n>0 lines 17−22, respectively. If tag is 0, the reader w, an instance 4 b4 r of InputStreamReader, is closed before the second loop st3 …...Postset:{q3} (line 14), and a java.io.IOException may be thrown Preset:{q1} c5:n<=1 b at line 19. For a reader, we are concerned with the regular 5 selected in DFS strategy property that method read is performed after method close. …...Postset:{q2,q3} Fig. 2 is the FSM, denoted by Mr, of this property, where Fig. 3. Difference between guided DSE and pure DSE init (object initialization, e.g., line 3), close and read method invocations are the events. We suppose that an event is atomic, i.e., no other events can be observed during its if(tag==0) and c4, c5 from st3 while(k++<n). Let execution. b1 : : : b5 be the corresponding off-path-branches of c1 : : : c5, Consider the initial input I1 = (m = 1; n = 1; tag = 1). respectively. Clearly, to reach state q3 of Mr, we need an The first iteration of DSE is shown by Fig.
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