syscalls

Lambda VM Syscalls (Guest SDK)

Guest-side library for programs that run inside the Lambda VM. Provides the syscalls and the default entry point that let a Rust program interact with the host: read private input, commit public output, halt, and invoke precompiles.

Published as lambda-vm-syscalls. Intended to be used from RISC-V (RV64IM) guest binaries cross-compiled with the toolchain described in the root README.md.

What it provides

Function	Purpose
commit(bytes: &[u8])	Append bytes to the public output that the verifier checks.
get_private_input() -> Vec<u8>	Read the host-supplied private input bytes (memory-mapped at 0xFF000000).
sys_halt() -> !	Terminate execution cleanly. Called automatically after main by the default entry point.
keccak_permute(state: &mut [u64; 25])	Keccak-f[1600] permutation precompile.

The crate also provides a default _start that initialises the allocator, calls main, and halts.

Note: the print_string syscall is temporarily unavailable — calling it in a guest will cause proof verification to fail. Tracked as a follow-up.

Example

A minimal guest that reads private input and commits a (non-secret) summary of it:

use lambda_vm_syscalls::syscalls;

pub fn main() {
    let input = syscalls::get_private_input();

    // Anything passed to `commit` becomes part of the proof's public output.
    // Don't echo private input here — commit a derived value instead.
    let len = (input.len() as u32).to_le_bytes();
    syscalls::commit(&len);
}

See executor/programs/rust/ for more example guests (fibonacci, keccak, hashmap, …).

Building a guest

Guests are compiled with a pinned nightly toolchain for the custom RISC-V target riscv64im-lambda-vm-elf.json. The simplest path is to drop a new project under executor/programs/rust/<name>/ and run make compile-programs-rust from the repo root.

See the root README.md for the full toolchain setup (sysroot, nightly pin, target spec).

Unsupported std functions

The following functions are stubbed and panic at runtime if called — Lambda VM does not provide stdin or command-line arguments:

• sys_read (so io::Read for Stdin is not available)
• sys_argc, sys_argv

To pass data into a guest, use get_private_input() instead.