ez-clang: experimental C++ REPL for bare metal

In 2021 a new remote-JIT layer “RemoteEPC” landed in LLVM’s OrcJIT library [0]. It separates serialization from transport, streamlines error behavior and integrates well with ExecutorProcessControl. Combined with the clean design and extensibility of ORCv2 and JITLink, it lowers the bar for building exotic out-of-process LLVM bitcode JITs. The ez-clang project [1] makes use of all these to build a pure out-of-process REPL specifically designed for very low-resource embedded devices. The executor endpoint on the device is very simple and fits into a few Kilobytes of memory. All heavy lifting happens in the JIT process on the host. I want to present my proof-of-concept implementation, which is based on a hacked-up version of cling [2] (bringing in Clang-integration, a command line and the concept of transaction-based incremental compilation). Right now, it supports a small selection of Cortex-M development boards. The smallest is the TeensyLC [3] with an ARMv6-M instruction set, 62kb Flash memory and 8kb RAM.
[0] https://github.com/llvm/llvm-project/commit/bb27e4564355
[1] https://echtzeit.dev/ez-clang
[2] https://github.com/root-project/cling
[3] https://www.pjrc.com/teensy/teensyLC.html