berm

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

berm is the OS for agent harnesses: it pins a guest by hash, compiles it once, instantiates it per invocation, and hands it only the syscalls it was given. bermd deploys programs and serves their tools over MCP, which is how Claude Code, Codex and OpenCode reach them.

rvtime is the RISC-V compiler underneath one of berm’s two backends — load an ELF, generate native code for it with Cranelift, call its exported functions, and let it call back. berm’s other backend is wasmtime, and it is the one a program is built for; rvtime is experimental.

The split is load-bearing rather than tidy. A backend knows about images, registers, and traps; berm knows about tools, manifests, and arguments. Every convention that makes a guest a berm program 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 program. 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 not published; cargo doc --open builds it from the source.