Our second contribution is the w system with a simple yet expressive checker interface, a set of builtin checkers, and a sound, checker and heuristicagnostic search algorithm that lever. Symbolic execution as a subject is hard to penetrate. All paths in the program form its execution tree, in which some paths are feasible and some are infeasible. The execution requires a selection of paths that are exercised by a set of data values. During a normal execution, the code follows a path defined by the current values of the program inputs e. I symbolic execution is the key technique used in darpa cyber grand challenge. From afar, fuzzing is a dumb, bruteforce method that works surprisingly well. It can test systems ranging from command line utilities to internet servers and distributed systems, thanks to its support for a symbolic posix os environment. Popular for nding software bugs and vulnerabilities. Symbolic execution the symbolic execution of a program is described in this section in an ideal sense, and then, in section 6, a particular practical system which has been built an ap proximation to the ideal is discussed. Symbolic execution with separation logic 53 conjunction. Combining unitlevel symbolic execution and systemlevel. As a result, the output values computed by a program are expressed as a function of the input symbolic values.
In this talk, i will discuss the use of symbolic execution for software testing, debugging and repair. Symbolic execution is used in conjunction with an automated theorem prover or constraint solver based on constraint logic. Selecta formal system for testing and debugging programs by symbolic execution. Cloud9 is a parallel symbolic execution engine that scales on sharednothing clusters of commodity hardware. Symbolic execution is a program analysis technique introduced in the 70s that has received renewed interest in recent years, due to algorithmic advances and increased availability of computational power and constraint solving technology. Generalized symbolic execution for model checking and testing. And the beauty of symbolic execution as a technique is that compared to testing, for example, it gives you the ability to reason about how your program is going. Symbolic execution symbolic execution refers to execution of program with symbols as argument. Selective symbolic execution vitaly chipounov, vlad georgescu, cristian zam.
Three decades later cristian cadar imperial college london c. Grr, a highthroughput fuzzer, and pysymemu pse, a binary symbolic executor with support for concrete inputs. Symbolic execution has become an effective program testing technique, providing a way to automatically generate inputs that trigger software errors ranging from low. This report documents the development of a system that enables symbolic execution of distributed software which uses network sockets for communication. During symbolic execution, program state consists of symbolic values for some memory locations. Symbolic execution, also called symbolic evaluation, has been studied as an independent software engineering tool for use after a program is written, but until recently little work has extended and integrated it into tho problem solving processes in design. Software testingdebugging is extremely time consuming, and hence techniques to automate debugging or program repair are of value. Using the discontinuity locking component, the user locks the model into a particular discrete mode defined by the current values of all of the inputs.
Symbolic execution is an approach at the core of many modern techniques to software testing, automatic program repair, and re verse engineering 6, 10, 20, 22, 25, 27. Aug 02, 2016 grrs strong determinism and isolation guarantees let us combine the strengths of grr with the sophistication of pse. In computer science, symbolic execution also symbolic evaluation or symbex is a means of analyzing a program to determine what inputs cause each part of a program to execute. Parallel symbolic execution for automated realworld. The key idea behind symbolic execution 6,12,23 is to use symbolic values, instead of concrete data values, as input values, and to represent the values of program variables as symbolic expressions over the symbolic values. A feasible execution path is a sequence of true and false, where a value of true respectively false at the thi position in the sequence denotes that the ith condi. Role of symbolic execution in software testing, debugging. Introduction recent tools 57,18,19 have applied symbolic execution to automated test case generation and bug.
Klee is a symbolic virtual machine built on top of the llvm compiler infrastructure, and available under the uiuc open source license. Symbolic components process systems engineering laboratory. Each execution state, labeled with an upper case letter, shows the statement to be executed, the symbolic store. Symbolic and concolic execution play important roles in a variety of security and software testing applications, e. Deconstructing dynamic symbolic execution microsoft research. Some insights about symbolic execution i execute programs with symbols. Testingverifying semanticspreserving changes, such as performance optimizations and porting to different platforms coveragetesting of arbitrary software patches. Section 4 gives our method for proving properties of java programs using symbolic execution and invariant generation and section 5 illustrates its application to the verification of several nontrivial java programs. Verification of java programs using symbolic execution and.
Role of symbolic execution in software testing, debugging and. This lab will introduce you to a powerful technique for finding bugs in software. Parallel symbolic execution for automated realworld software. Verifying systems rules using ruledirected symbolic. Symbolic execution is a software testing technique that is useful to aid the generation of test data and in proving the program quality.
Symbolic execution georgia institute of technology. The general idea behind symbolicconcolic execution is to represent. If the correctness criteria for the given program is described by a set of test cases, we will show that. A fuzzer and a symbolic executor walk into a cloud trail of. A fuzzer and a symbolic executor walk into a cloud trail. Symbolic execution and program testing virginia tech. Accelerating array constraints in symbolic execution. Tools based on symbolic execution have found serious errors and security vulnerabilities in various systems. Compositional symbolic execution using finegrained summaries. Verifying systems rules using ruledirected symbolic execution.
By the end of this lab, you will have a symbolic execution system that can take the zoobar web. I dart godefroid and sen, pldi 2005 introduce dynamic. Bushnell, karen gundyburlet, michael lowry nasa ames research center moffett field, ca 94035 corina. Symbolic execution verification condition generation fsoft ivancic et al. Symbolic execution for software testing in practice. We know that a will continue to hold in the rest of the heap if.
Symbolic execution a program analysis technique that executes a program with symbolic rather than concrete input values. Coupling distributed and symbolic execution for natural. Execution symbolic execution hybrid fuzzing figure 1. While the key idea behind symbolic execution was introduced more than three decades ago,6,12,23 it has only recently been. This can be a good way to audit your application for security vulnerabilities so that you can then fix them. Symbolic execution tree of function foobar given in figure 1. Symbolic execution as empirical studies tool web application security checker enhancement to abstractionbased static analysis program synthesis tool all of these take advantage of sym exec strengths, and try to avoid drawbacks 7. Parallel symbolic execution for automated realworld software testing stefan bucur vlad ureche cristian zam. An interpreter follows the program, assuming symbolic values for inputs rather than obtaining actual inputs as normal execution of the program would. In software testing, symbolic execution is used to generate a test input for each feasible execution path of a program. For more information on what klee is and what it can do, see the osdi 2008 paper. Symbolic execution for evolving software active area of research in the software reliability group at imperial three main directions so far. Symbolic execution umd department of computer science. The general idea behind symbolic concolic execution is to represent.
Unlike concrete execution, where the taken path is determined by the input, in symbolic execution the program can take any feasible path. Looking closer at compositional symbolic execution. After discussing the threats to validity in section 7, we demonstrate the application of dgse in section 8. Redundant state detection for dynamic symbolic execution. Concolic testing a portmanteau of concrete and symbolic is a hybrid software verification technique that performs symbolic execution, a classical technique that treats program variables as symbolic variables, along a concrete execution testing on particular inputs path.
Dynamic symbolic execution dse is a wellknown technique for automatically generating tests to achieve higher levels of coverage in a program. Theres a lot of that academic projects that have made a lot of real world impact by discovering important bugs in open source software, for example, by relying on symbolic execution. I concrete execution versus symbolic execution i symbolic execution tree i applications of symbolic execution. We tackled the harder problem and produced two productionquality bugfinding systems. We explore the design and implementation of the essential facilities to simulate distributed software namely, the networking and the lesystem layers. Generalized symbolic execution for model checking and.
Second, we give a novel symbolic execution algorithm that handles dynamically allocated structures e. Grr can snapshot a running program, enabling pse to jumpstart symbolic execution from deep within a given program execution. Classic symbolic execution 5 execute the program on symbolic values. Dec 09, 20 software testingdebugging is extremely time consuming, and hence techniques to automate debugging or program repair are of value. A symbolic execution tree depicts all executed paths during the symbolic execution. Then, we present dgse in section 5, followed by experimental results in section 6. Generalized symbolic execution for model checking and testing sarfraz khurshid1, corina s. During symbolic execution, the path condition is used to collect constraints on the program expressions, and describes the current path through the symbolic execution tree. Cloud9 builds upon the klee symbolic execution engine. Resurgence of symbolic execution the block issues in the past.
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