Static analysis vs. symbolic execution in implementation

Question

What is the difference between implementation of static analysis and symbolic execution?

Answer 1

Static analysis is any off-line computation that inspects code and produces opinions about the code quality. You can apply this to source code, to virtual machine code for Java/C#/... virtual machine instruction sets, and even to binary object code. There is no "one" static analysis (although classic compiler control and dataflow often figure prominently as foundation machinery for SA); the term collectively applies to all types of mechanisms that might be used offline.

Symbolic execution is a specific kind of off-line computation that computes some approximation of what the program actually does by constructing formulas representing the program state at various points. It is called "symbolic" because the approximation is usually some kind of formula involving program variables and constraints on their values.

Static analysis may use symbolic execution and inspect the resulting formula. Or it may use some other technique (regular expressions, classic compiler flow analyses, ...) or some combination. But static analysis does not have to use symbolic execution.

Symbolic execution may be used just to show an expected symbolic result of a computation. That isn't static analysis by the above definition because there isn't any opinion formed about how good that result is. Or, the formula may be subjected to analysis, at which point it becomes part of a static analysis. As a practical matter, one may use other program analysis techniques to support symbolic execution ("this formula for variable is propagated to which reads of variable x?" is a question usually answered well by flow analysis).

You may insist that static analysis is any offline computation over your source code, at which point symbolic execution is just a special case. I don't find this definition helpful, because it doesn't discriminate between use cases well enough.

Answer 2

I really like this slide by Julian Cohen's Contemporary Automatic Program Analysis talk. In a nutshell, people like to divide program analysis into two broad categories of static and dynamic analysis. But there is really a broad spectrum of program analysis techniques that range from static to dynamic and manual to fully automatic. Symbolic execution is an interesting technique that falls somewhere in between static and dynamic analysis and is generally applied as a fully automatic approach.