An Overview of the Extended Static Checking System

The Extended Static Checking system (henceforth ESC) is a checker aimed at statically detecting simple errors in programs; e.g., NIL dereferences, out-of-bounds array indices, or simple deadlocks or race conditions in concurrent programs. ESC attempts to achieve these fairly modest goals using a quite general program verification framework. The user annotates the program being checked with specifications; a verification condition generator transforms the program and specification into a logical formula whose validity ensures the absence of the errors being considered. This formula is passed to an automatic theorem prover (called Simplify) developed expressly for ESC. If the prover is unable to prove that the errors do not occur, it returns (roughly) an assignment of values to program variables that falsifies the formula. This information can be presented to the programmer, giving information about the error somewhat akin to what a debugger provides when examining a core file left by a runtime occurrence of the error.