Many APIs enable cross-platform system development by abstracting over the details of a platform, allowing application developers to write one implementation that will run on a wide variety of platforms. Unfortunately, subtle differences in the behavior of the underlying platforms make cross-platform behavior difficult to achieve. As a result, applications using these APIs can be plagued by bugs difficult to observe before deployment. These portability bugs can be particularly difficult to diagnose and fix because they arise from the API implementation, the operating system, or hardware, rather than application code. This paper describes CheckAPI, a technique for detecting violations of cross-platform portability. CheckAPI compares an application's interactions with the API implementation to its interactions with a partial specification-based API implementation, and does so efficiently enough to be used in real production systems and at runtime. CheckAPI finds latent errors that escape pre-release testing. This paper discusses the subtleties of different kinds of API calls and strategies for effectively producing the partial implementations. Validating CheckAPI on JavaScript, the Seattle project's Repy VM, and POSIX detects dozens of violations that are confirmed bugs in widely-used software.

Software bugs often arise because of differences between what developers think their system does and what the system actually does. These differences frustrate debugging and comprehension efforts. We describe Perfume, an automated approach for inferring behavioral, resource-aware models of software systems from logs of their executions. These finite state machine models ease understanding of system behavior and resource use.