A Run-Time Type-Checking Debugger for C

This document outlines progress to date on the run-time type-checking project funded in part by IBM. The project has been carried out during the last year by Alexey Loginov and Suan Yong, under the supervision of Professors Susan Horwitz and Thomas Reps. The goal of the project is the design and implementation of a debugging tool based on dynamic type checking. The major accomplishment during the last year has been an implementation of the tool for the (complete) ANSI C language. The tool instruments a program to monitor the type stored in each memory location (which may differ from the static type of that location due to the use of unions, pointers, and casting). Whenever a value is written into a location, the location’s run-time type tag is updated to match the type of the value. Also, the location’s static type is compared with the value’s type; if there is a mismatch, a warning message is issued. Whenever the value in a location is used, its run-time type tag is checked, and if the type is inappropriate in the context in which the value is being used, an error message is issued. In preliminary tests, the tool has been used to find bugs in several Solaris utilities. The information provided by the tool is usually succinct and precise in showing the error location. The following activities (discussed in more detail below) are planned for the coming year: