nalysius / build-rust

Script helper for building rustc and cargo from source on OpenBSD (without rustup)

build-rust

build-rust is a shell script for getting a Rust beta or nightly running on OpenBSD.

The script works by using the stable Rust from the OpenBSD package repo to build a beta Rust, then (if you want a nightly) it uses this beta Rust to build a nightly Rust. It also deals with ensuring the right cargo version is used at each stage.

Quick Start

First, choose a program to allow build-rust to be root. You usually want either doas or sudo. E.g.:

echo "SUDO=doas" > ~/.build_rust.conf

Next:

$ ./build.sh init

This step uses the SUDO command you chose in the first step to install some packages. Please read the script to ensure you are happy with the commands that will be run as root.

Now run:

$ ./build.sh <target>

Where <target> is either beta or nightly. If you choose nightly but have not yet built beta, then beta will be built first automatically.

Once this is done you will have a working Rust environment (including cargo) in install_dir/<target>. If you want this to be your default rustc and cargo, then you probably want to add install_dir/<target>/bin to your PATH in your shell rc.

Why is the Installed Cargo Old?

The script uses the version of cargo indicated in upstream src/stage0.txt. This is not necessarily the newest cargo, but is guaranteed to work for bootstrapping.

If you would like a newer cargo, you can either manually build one off the upstream master branch, or you can use the bootstrap cargo to install a new one in ~/.cargo/bin:

$ cargo install cargo

If you want that as your default cargo, don't forget to add it to the PATH.

Why do we Need this Script?

Why not just use rustup? In short, OpenBSD has tier 3 Rust support, meaning that the Rust upstream does not make binaries available via rustup. There are a couple of reasons for this.

Reason 1: Cross compiling.

Under normal circumstances, Rust upstream would cross compile beta and nightly Rust on their Linux machines, making the resulting binaries available via rustup. However, OpenBSD has a modified linker meaning that targeting OpenBSD with a cross compiler is not straightforward.

Reason 2: No Backward Compatibility

OpenBSD makes no attempt to be backward compatible. At any given time there are two supported stable releases of OpenBSD, and a frequently regenerated developer version called -current. Generally speaking, binaries from an older stable release do not run on a newer stable release. Furthermore, there is no guarantee that the binary built on last week's -current will work on this week's. Compatibility breakage can occur not only at the library level, but also at the ABI level.

Even if the Rust upstream could cross compile to OpenBSD, it's not clear which version's of OpenBSD would be useful to target.