Physical type checking for C

  • Authors:

  • Satish Chandra;Thomas Reps

  • Affiliations:

  • Software Production Research Dept., Bell Laboratories, Lucent Technologies;Computer Sciences Dept., University of Wisconsin-Madison

  • Venue:
  • Proceedings of the 1999 ACM SIGPLAN-SIGSOFT workshop on Program analysis for software tools and engineering
  • Year:
  • 1999

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Abstract

The effectiveness of traditional type checking in C is limited by the presence of type conversions using type casts. Because the C standard allows arbitrary type conversions between pointer types, neither C compilers, nor tools such as lint, can guarantee type safety in the presence of such type conversions. In particular, by using casts involving pointers to structures (C structs), a programmer can interpret any memory region to be of any desired type, further compromising C's weak type system. Not only do type casts make a program vulnerable to type errors, they hinder program comprehension and maintenance by creating latent dependencies between seemingly independent pieces of code.To address these problems, we have developed a stronger form of type checking for C programs, called physical type checking. Physical type checking takes into account the layout of C struct fields in memory. This paper describes an inference-based physical type checking algorithm. Our algorithm can be used to perform static safety checks, as well as compute useful information for software engineering applications.