berm

Two things ship from this repository, and this book covers both.

berm is a sandbox for harnesses: it pins a guest by hash, compiles it once, instantiates it per invocation, and hands it only what it was given. bermd deploys harnesses and serves their tools over MCP.

rvtime is the RISC-V compiler underneath — load an ELF, generate native code for it with Cranelift, call its exported functions, and let it call back.

The split is load-bearing rather than tidy. rvtime knows about ELFs, registers, and traps; berm knows about tools, manifests, and arguments. Every convention that makes a guest a harness lives on the berm side, which is what leaves rvtime usable for a guest that is not one.

How to read this

Start with berm to write or run a harness. Its five chapters cover what the sandbox guarantees, how to write a guest against it, what an image declares about itself, how one travels between machines, and how the service serves it.

Read rvtime to change the compiler, or when something surprises you and the question is whether it was deliberate. Its examples are real programs in the repository, compiled by CI and included here by reference rather than pasted, so what you read is what runs.

API documentation is generated from the source and lives at /api; it is not duplicated here.