Developing and debugging software for microcontrollers can be rather challenging. There are three main challenges in debugging microcontroller software. First, microcontrollers are often programmed in low-level languages such as C or C++. Second, debugging tools are often very limited or simply non-existent. Finally, the non-deterministic nature of sensors connected to the microcontrollers, makes it hard to reproduce bugs.

These challenges make finding and reproducing bugs in microcontroller programs tedious. To overcome these challenges, we propose building a new debugger for microcontrollers based on the ideas of multiverse debugging, which allows all non-deterministic execution paths of a program to be explored. Our approach builds upon two main ideas: Time Travel Debugging and Concolic Debugging. Time Travel Debugging allows a developer to explore an execution both forwards and backwards in time. Concolic Debugging allows a developer to debug a specifically chosen execution of a non-deterministic program. When doing so concolic execution is used to mitigate the problem of state explosion. Our novel approach that combines Time Travel and Concolic Debugging is what we call Concolic Multiverse Debugging.

In this demo we present our prototype Concolic Multiverse Debugger for the WARDuino WebAssembly virtual machine. We show how this prototype can be used to debug a robot powered by an STM32 microcontroller.