Integrating Symbolic Execution, Debugging and Verification

In modern software development, almost all activities are centered around an integrated development environment (IDE). Besides the main use cases to write, execute and debug source code, an IDE serves also as front-end for other tools involved in the development process such as a version control system or an application lifecycle management. Independent from the applied development process, the techniques to ensure correct software are always the same. The general goal is to find defects as soon as possible, because the sooner a defect is found, the easier and cheaper it is to fix. In the first place, the programming language helps to prevent some kinds of defects. Once something is written, it is effective to review it not only to find defects, but also to increase its quality. Also tools which statically analyze the source code help to find defects automatically. In addition, testing is used to ensure that selected usage scenarios behave as expected. However, a test can only show the presence of a failure and not its absence. To ensure that a program is correct, it needs to be proven that the program complies to a formal specification describing the desired behavior. This is done by formal verification tools. Finally, whenever a failure is observed, debugging takes place to locate the defect. This thesis extends the software development tool suite by an interactive debugger based on symbolic execution, a technique to explore all feasible execution paths up to a given depth simultaneously. Such a tool can not only be used for classical debugging activities, but also during code reviews or in order to present results of an analysis based on symbolic execution. The contribution is an extension of symbolic execution to explore the full program behavior even in presence of loops and recursive method calls. This is achieved by integrating specifications in form of loop invariants and methods contracts into a symbolic execution engine. How such a symbolic execution engine based on verification proofs can be realized is presented as well. In addition, the presented Symbolic Execution Debugger (SED) makes the Eclipse platform ready for debuggers based on symbolic execution. Its functionality goes beyond that of traditional interactive debuggers. For instance, debugging can start directly at any method or statement and all program execution paths are explored simultaneously. To support program comprehension, program execution paths as well as intermediate states are visualized. By default, the SED comes with a symbolic execution engine implemented on top of the KeY verification system. Statistical evidence that the SED increases effectiveness of code reviews is gained from a controlled experiment. Another novelty of the SED is that arbitrary verification proofs can be inspected. Whereas traditional user interfaces of verification tools present proof states in a mathematical fashion, the SED analyzes the full proof and presents different aspects of it using specialized views. A controlled experiment gives statistical evidence that proof understanding tasks are more effective using the SED by comparing its user interface with the original one of KeY. The SED allows one to interact with the underlying prover by adapting code and specifications in an auto-active flavor, which creates the need to manage proofs directly within an IDE. A presented concept achieves this, by integrating a semi-automatic verification tool into an IDE. It includes several optimizations to reduce the overall proof time and can be realized without changing the verification tool. An optimal user experience is achieved only if all aspects of verification are directly supported within the IDE. Thus a thorough integration of KeY into Eclipse is presented, which for instance includes in addition to the proof management capabilities to edit JML specifications and to setup the needed infrastructure for verification with KeY. Altogether, a platform for tools based on symbolic execution and related to verification is presented, which offers a seamless integration into an IDE and furthers a usage in combination. Furthermore, many aspects, like the way the SED presents proof attempts to users, help to reduce the barrier of using formal methods.