Many modern software systems are designed to be highly configurable, which increases flexibility but can make programs hard to test, analyze, and understand. We present an initial empirical study of how configuration options affect program behavior. We conjecture that, at certain levels of abstraction, configuration spaces are far smaller than the worst case, in which every configuration is distinct. We evaluated our conjecture by studying three configurable software systems: vsftpd, ngIRCd, and grep. We used symbolic evaluation to discover how the settings of run-time configuration options affect line, basic block, edge, and condition coverage for our subjects under a given test suite. Our results strongly suggest that for these subject programs, test suites, and configuration options, when abstracted in terms of the four coverage criteria above, configuration spaces are in fact much smaller than combinatorics would suggest and are effectively the composition of many small, self-contained groupings of options.

There are many proposals for language techniques to control aliasing and encapsulation in object oriented programs, typically based on notions of object ownership and pointer uniqueness. Most of these systems require extensive manual annotations, and thus there is little experience with these properties in large, existing Java code bases. To remedy this situation, we present Uno, a novel static analysis for automatically inferring ownership, uniqueness, and other aliasing and encapsulation properties in Java. Our analysis requires no annotations, and combines an intraprocedural points-to analysis with an interprocedural, demand-driven predicate resolution algorithm. We have applied Uno to a variety of Java applications and found that some aliasing properties, such as temporarily lending a reference to a method, are common, while others, in particular field and argument ownership, are relatively uncommon. As a result, we believe that Uno can be a valuable tool for discovering and understanding aliasing and encapsulation in Java programs.