Contributions for Improving Debugging of Kernel-level Services in a Monolithic Operating System

Overview & Synopsis

Despite the existence of an overwhelming amount of research on the quality of system software, Operating Systems are still plagued with reliability issues mainly caused by defects in kernel-level services such as device drivers and file systems. Studies have indeed shown that each release of the Linux kernel contains between 600 and 700 faults, and that the propensity of device drivers to contain errors is up to seven times higher than any other part of the kernel. These numbers suggest that kernel-level service code is not sufficiently tested and that many faults remain unnoticed or are hard to fix by non-expert programmers who account for the majority of service developers. This thesis proposes a new approach to the debugging and testing of kernel level services focused on the interaction between the services and the core kernel. The approach tackles the issue of safety holes in the implementation of kernel API functions. For Linux, we have instantiated the Diagnosys automated approach which relies on static analysis of kernel code to identify, categorize and expose the different safety holes of API functions which can turn into runtime faults when the functions are used in service code by developers with limited knowledge on the intricacies of kernel code. To illustrate our approach, we have implemented Diagnosys for Linux 2.6.32 and shown its benefits in supporting developers in their testing and debugging tasks.