RFC: add draft to support WebAssembly within the kernel

[stlankes]

This is a proof-of-concept to run compiled WebAssembly code within the kernel. The current solution based on wasmtime.

The current example use a simple Rust function to calculate a Fibonacci number:

// Calculating fibonacci numbers
#[no_mangle]
pub extern "C" fn fibonacci(n: u64) -> u64 {
    match n {
        0 => 0,
        1 => 1,
        _ => fibonacci(n - 1) + fibonacci(n - 2),
    }
}

The rust code has to compile to WebAssembly. Following example can be used to create WebAssembly code:

cargo build --target wasm32-unknown-unknown --release

This following subcommand is used to Ahead-Of-Time (AOT) compile a WebAssembly module to produce a compiled wasm (.cwasm) file.

wasmtime compile --target x86_64-unknown-none -W threads=n -W simd=n -W relaxed-simd=n -W tail-call=y -o fib.cwasm fib.wasm

The proof-of-concept includes fib.cwasm as array of bytes. The kernel loads the module, checks the module and call the function fibonacci.