WHATSAT: Dynamic Heap Type Inference for Program Understanding and Debugging

C programs can be difficult to debug due to lax type enforcement and low-level access to memory. The authors present a dynamic analysis for C that checks heap snapshots for consistency with program types. The approach builds on ideas from physical sub-typing and conservative garbage collection. They infer a program-defined type for each allocated storage location or identify "Untypable" blocks that reveal heap corruption or type safety violations. The analysis exploits symbolic debug information if present, but requires no annotation or recompilation beyond a list of defined program types and allocated heap blocks. They have integrated the analysis into the GNU Debugger (Gdb), and describe the initial experience using this tool with several small to medium-sized programs.