Software Reliability 2016/2017

MEng 4 and MSc selected specialisms, Department of Computing
Imperial College London

Software Reliability (440)

Open to MEng 4 students and MSc in Computing (Advanced Computing, Software Engineering and Secure Software Systems specialisms) students, this course provides an overview of exciting recent research into techniques and tools that aim to help developers improve the reliability of their software.

Society is becoming ever more reliant on software and software-controlled systems. Some of this software is safety-critical, e.g., the software used to control cars, aeroplanes and other high-speed transport. Defects in safety-critical software can lead to serious injury or death. A much larger volume of software is business-critical, e.g., software that runs in mobile phones, powers web servers and manages data centers. Defects in this type of software can lead to significant financial losses. Underpinning all of these areas is systems software: the low-level operating systems, compilers, device drivers and networking software on which complex systems are built. This foundational role means that the reliability of systems software is of primary importance.

Three of the main techniques used in industrial and open source projects to improve software reliability are:

• Manual testing: Manually crafting a suite of tests to exercise a software system to a reasonably high degree, e.g., covering a high percentage of program statements.
• Code reviews: Requiring that source code additions or modifications (patches) are reviewed by experienced developers before being committed to the code base.
• Coding standards: Requiring that all developers adhere to a set of rules when writing or maintaining code. Coding standards can improve source code readability, making it easier to spot defects, and may ban the use of programming idioms that are arguably dangerous.

Rigorous manual testing, code reviews and adherence to standards are essential to the success of large software projects, but they all suffer from two common problems:

• They depend fundamentally on human reasoning and judgement. Humans are clever, but software can be devilishly complex. It is easy for subtle defects to creep into a project despite adherence to coding standards, and to evade manual testing and code review.
• They do not provide guarantees. A test suite can demonstrate that certain executions of a software system do not exhibit defects, but provides no further guarantee. For safety- (and often business-) critical systems this may not be enough: it is highly desirable to have a guarantee of defect freedom; ideally an absolute guarantee, but at least a guarantee that system executions have been systematically checked up to some well-defined bound.

The focus of this course is on automatic techniques for improving software reliability which go beyond manual testing. The course will cover:

• Verification condition generation
• Procedure summaries
• Bounded model checking
• Dynamic symbolic execution
• Constraint solving
• Invariant generation
• Systematic testing for concurrent programs
• The lockset algorithm
• Undefined behaviour, compiler bugs and unstable code
• Introduction to security and stack canaries
• Safe C compilers
• Control-flow, data-flow and write integrity

The constraint solving topic is at the heart of many of the techniques we will study, as a common approach is to encode program behaviours as logical formulae to be discharged to a solver. Dramatic advances in the power of constraint solvers in recent years has made it possible to apply relevant techniques to larger and larger software systems.