In this section we describe how to apply it to test generation and in problems about security bugs in software. Thus, the concrete execution of the system can be e. Generalized symbolic execution for model checking and testing sarfraz khurshid1, corina s. Symbolic executors work by running the program, computing over both concrete values and expressions that include symbolic values, which are. In parallel, execute symbolically and solve constraints. The major bene t of dse is to simplify the construction of a symbolic execution tool by leveraging the concrete execution behavior given by actually running the program. Mixed concrete and symbolic execution is an important technique for. 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. Second, dse uses concrete values from the execution pi in place of symbolic expressions whenever symbolic reasoning is not possible or desired 1,8. Directed automated random testing dart 20, or concolic testing 37 performs symbolic execution dynamically, while the program is executed on some concrete input values. Finding bios vulnerabilities with symbolic execution and. While concolic testing has shown promising results in software veri.
Combining unitlevel symbolic execution and systemlevel. Jun 06, 2017 symbolic execution is a powerful technique to systematically explore paths possibly all of a software program. Generate inputs to other paths than the concrete one along the way. However, existing symbolic execution techniques are limited to examining one execution path at a time, in which symbolic variables reflect only direct data dependencies. During symbolic execution, the program reads a symbolic value e. As a result, the outputs computed by a program are. We present below two such extensions, and then discuss the key advantages they provide. 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. Symbolic execution discovers all possible execution paths simultaneously. So lets see how we use these symbolic expressions in an example execution. Symbolic java pathfinder symbolic execution of java. From afar, fuzzing is a dumb, bruteforce method that works surprisingly well, and symbolic execution is.
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. Symbolic execution a program analysis technique that executes a program with symbolic rather than concrete input values. Awanish pandey, phani raj goutham kotcharlakota, and subhajit roy. Citeseerx loopextended symbolic execution on binary programs. Symbolic execution and program testing virginia tech. In this latter scenario, a fuzzer selects interesting inputs and symbolic execution merely follows a fixed path dictated by a given concrete program input. Asymbolicexecutionandautomatic test generation toolfor. Intuitive understanding of symbolic execution i execute programs with symbols.
In a concrete execution, a program is run on a specific input and a single control flow path is explored. A survey of new trends in symbolic execution for software testing and analysis. Symbolic execution 4,1 performs the execution of a program on symbolic open inputs. As a result, the output values computed by a program are expressed as a function of the input symbolic values. Instead of using concrete inputs, symbolic execution executes a program with symbolic inputs. Citeseerx loopextended symbolic execution on binary. Three decades later garnered a lot of attention in recent years as an effective technique for generating highcoverage test suites and for finding deep.
On the lefthand side well consider concrete memory, well look at how a concrete, that is normal execution of the program might go, and then we look at how it might go for our symbolic. Furthermore, it allows for easy extension with other analyses that maintain both concrete and symbolic data such as concolic execution 3. Symbolic execution symbolic execution 28 is a form of program analysis that uses symbolic values instead of actual data as inputs and symbolic expressions to represent the values of program variables. We have developed symbolic java pathfinder a symbolic execution framework that implements a nonstandard bytecode interpreter on top of the java pathfinder model. Symbolic execution with mixed concretesymbolic solving. In computer science, symbolic execution also symbolic evaluation is a means of analyzing a program to determine what inputs cause each part of a program to execute. An interpreter follows the program, assuming symbolic values for inputs rather than obtaining actual inputs as normal execution of the program would, a case of abstract interpretation. However, existing symbolic execution techniques are limited to examining one execution path at a time, in which symbolic. In particular, we are now working on functional reactive synthesis, symbolic execution engine for haskell, and verification of configuration files. The solutions to path conditions are the test inputs that will assure that the program under test runs along a particular concrete path.
We describe a prototype that can symbolically execute arbitrary portions of a full system, including applications, libraries, operating system, and device drivers. This is achieved by the use of symbolic in lieu of concrete values resulting in a symbolic execution tree. Symbolic execution, software testing, fuzzing acm reference format. I symbolic execution is the key technique used in darpa cyber grand challenge. Symbolic execution is a well known program analysis technique, which represents values of program variables with symbolic values in stead of concrete initialized data and manipulates expressions involving sym. It seamlessly transitions back and forth between symbolic and concrete execution, while. Each execution state, labeled with an upper case letter, shows the statement to be executed, the symbolic store. Unlike formal methods, concolic testing is scalable since it can avoid state space explosion by exploring one execution path at a time. During execution, a symbolic execution engine accumulates a set of constraints on the symbolic inputs. For instance, first, a software under test, such as bpua 101, may be executed using concrete values e. We tackled the harder problem and produced two productionquality bugfinding systems. Basic symbolic execution program analysis coursera. A survey of new trends in symbolic execution for software testing and analysis article in international journal on software tools for technology transfer 114.
It seamlessly transitions back and forth between symbolic and concrete execution, while transparently converting system state from symbolic to concrete and back. In contrast, symbolic execution can simultaneously explore multiple paths that a program could take under different inputs. Symbolic execution allows us to execute a program through all possible execution paths, thus achieving all possible path conditions path condition the set of logical constraints that takes us to a specific point in the execution. Rose is a yale computer science laboratory that focuses on using formal methods to improve software reliability. The term concolic is a portmaneau of concrete and symbolic, which indicates that the concolic execution includes concrete execution and symbolic execution. In this paper, we propose a novel technique for statespace exploration of software that maintains an ongoing interaction with its environment. However, existing symbolic execution techniques are limited to examining one execution path at a time, in which symbolic variables re.
By cristian cadar and koushik sen symbolic execution for software testing. I replace symbolic variables with concrete values that satisfy the path condition i so, could actually do system calls. Concolic testing is a software testing technique that simultaneously combines concrete execution of a program given specific input, along specific paths with symbolic execution generating new. Symbolic execution is an attractive approach to solving line reachability. During a normal execution concrete execution, the program would read a concrete input value e. 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. In concolic testing, what does concrete execution mean. Execution would then proceed with the multiplication and the conditional branch, which would evaluate to false and print ok. Popular for nding software bugs and vulnerabilities. We now discuss prominent applications of symbolic execution techniques to these domains. Our technique makes symbolic execution practical for large software that runs in real environments, without requiring explicit. Concolic testing is a software testing technique combining concrete execution of a program given specific input, along specific paths with symbolic execution generating new test inputs that. Selecta formal system for testing and debugging programs by symbolic execution. Aug 02, 2016 automating the process is even harder.
Jun 18, 2018 the term concolic is a portmaneau of concrete and symbolic, which indicates that the concolic execution includes concrete execution and symbolic execution. Programstatespace explorationis central to software security, testing, and veri. Some insights about symbolic execution i execute programs with symbols. Symbolic execution tree of function foobar given in figure 1. Grr, a highthroughput fuzzer, and pysymemu pse, a binary symbolic executor with support for concrete inputs. The symbolic execution debugger sed is a platform for symbolic execution in general and allows to interactively debug programs based on symbolic execution. Combining symbolic execution and model checking for data. Concolic execution is a mix between concrete execution and symbolic execution, with the purpose of feasibility. Loopextended symbolic execution can be used to get better results from mixed concrete and symbolic execution whenever it is used with programs in which loops occur. Symbolic execution is a powerful technique to systematically explore paths possibly all of a software program. Systematic comparison of symbolic execution systems. In particular, section 8 discusses how automated test case generation and test suite optimization benefited from advances in constraint solving, hybrid concrete symbolic execution, directed symbolic execution, and the symbolic modeling of nonstandard programming artifacts like databases. Symbolic execution is used in conjunction with an automated theorem prover or constraint solver based on constraint logic. Symbolic executors work by running the program, computing over both concrete.
The process begins with certain variableslocationstypically, those. A survey of new trends in symbolic execution for software. Dynamic symbolic execution 14, 15 dse is a widely accepted and effective approach for automatic test data generation. Scalable hardware trojan activation by interleaving. We describe an approach to testing complex safety critical software that combines unitlevel symbolic execution and systemlevel concrete execution for generating test.
It characterizes each program path it explores with a path condition which denotes a series of branching decisions. Symbolic execution for software testing in practice. For example, after line 7 in the example code, two instances of symbolic execution are created with path constraints x 0 2y 0 and x 0 6 2 y 0. However, existing symbolic execution techniques are limited to examining one execution path at a time, in which symbolic variables. Deferred concretization in symbolic execution via fuzzing. Hence, in most cases concrete executions can only underapproximate the analysis of the property of interest. Also called dynamic symbolic execution instrument the program to do symbolic execution as the program runs i. We describe an approach to testing complex safety critical software that combines unitlevel symbolic execution and systemlevel concrete execution for generating test cases that satisfy userspecified testing criteria. In this paper, we use automata learning to enable symbolic execution in the presence of blackbox components. Our technique uses a combinationof symbolic and concrete execution to build an abstract model of the ana. It intertwines traditional symbolic execution 16 with concrete execution, and explores as many program paths as possible to generate test cases by solving path constraints. Mixed concrete and symbolic execution is an important technique for finding and understanding software bugs, including securityrelevant ones. During execution, a symbolic execution engine accumulates a set of constraints on the symbolic.