• FreeBSD machine
• Rust nightly
• Xargo

I recommend using rustup for installing and handling different versions of Rust.

Rust

See https://www.rustup.rs/

Xargo

$ cargo install xargo

Setting Rust nightly

Do in crate root:

$ rustup override set nightly

This folder is the Cargo root for the module itself.

Here are all the dependency crates that are not available on crates.io.

core is built and handled completely by Xargo.

Copied from Rust source code, unmodified.

Copied from Rust source code, unmodified.

Copied from Rust source code, unmodified.

Copied from Rust source code.

Added kern_malloc.rs which is the FFI bindings to kernel's malloc functions.

Modified lib.rs to use said functions.

A minimal implementation of std for the echo module. FFI bindings are generated on build. Safe bindings exists for things necessary for this code to run.

Check build.sh script if you like to make any changes then run

$ ./build.sh

If build was successful there should be a hello.ko file in the root folder. Load with

$ sudo kldload ./hello.ko

$ cat /dev/rustmodule  
Default Message :)  
$ echo Hello > /dev/rustmodule   
Read 6 bytes. Setting new message to "Hello\n"  
$ cat /dev/rustmodule  
Hello  
$ sudo kldunload hello  

If there are any bugs or faulty code the kernel will most likely hang.

I recommend testing the module in a virtual machine.

It keeps your system safe and it makes it easier to develop and test.