Open Source Summit Europe 2024

Bringing an existing codebase into MISRA compliance is known to be a difficult, risky and time-consuming task. Yet, when a product needs a functional safety certification and rewriting the software is out of question, this is a necessity. Such an endeavor requires facing multiple tradeoffs and, consequently, lots of experience both on the codebase and on MISRA. The choices between deviating the guideline, and the (often, many) ways in which code may be changed and deviations may be formulated, are tough and with consequences that are not immediately evident. The situation is particularly interesting in the case of open-source software, where additional challenges have to be faced. In this presentation, we illustrate our experience and the several lessons learned while undertaking MISRA compliance work in open-source projects, most notably the Zephyr RTOS and the Xen hypervisor, both used in many embedded systems. Key take-home points include: effective deviation strategies and mechanisms; dealing with the MISRA C essential type model (guidelines related to that account for many of the violations in existing codebases); interaction with open-source communities.