Bringing Segmented Stacks to Embedded Systems

Microcontrollers are the heart of embedded systems. Due to cost and power constraints, they do not have memory management units (MMUs) or even memory protection units (MPUs). As a result, embedded software faces two related challenges both concerned with the stack. First, in a multi-tasking environment, physical memory used by the stack is usually statically allocated per task. Second, a stack overflow is difficult to detect for lower-end microcontrollers without an MPU. In this work, we argue that segmented stacks, a notion investigated and subsequently dismissed for systems with virtual memory, can solve both challenges for embedded software. We show that many problems with segmented stacks vanish on embedded systems and present novel solutions to the rest. Importantly, we show that segmented stacks, combined with Rust, can guarantee memory safety without MMU or MPU. Moreover, segmented stacks allow memory to be dynamically allocated to per-task stacks and can improve memory efficiency when combined with proper scheduling.

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In Proceedings of the 24th International Workshop on Mobile Computing Systems and Applications