kirdy/BSD.md

Building Rust embedded firmware on BSD

Using the Rust stable compiler from the BSD ports is mostly a matter of removing the arbitrary limitations that have been built into the Rust toolchain.

Get rid of the "nightly toolchain" check in cargo-xbuild:

diff --git a/src/lib.rs b/src/lib.rs
index 204ad8f..9c61e39 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -157,28 +157,11 @@ pub fn build(args: Args, command_name: &str, crate_config: Option<Config>) -> Re
         })
     })?;

-    // We can't build sysroot with stable or beta due to unstable features
     let sysroot = rustc::sysroot(verbose)?;
-    let src = match meta.channel {
-        Channel::Dev => rustc::Src::from_env().ok_or(anyhow!(
+    let src = rustc::Src::from_env().ok_or(anyhow!(
             "The XARGO_RUST_SRC env variable must be set and point to the \
-             Rust source directory when working with the 'dev' channel",
-        ))?,
-        Channel::Nightly => {
-            if let Some(src) = rustc::Src::from_env() {
-                src
-            } else {
-                sysroot.src()?
-            }
-        }
-        Channel::Stable | Channel::Beta => {
-            bail!(
-                "The sysroot can't be built for the {:?} channel. \
-                 Switch to nightly.",
-                meta.channel
-            );
-        }
-    };
+             Rust source directory",
+        ))?;

     let cmode = if let Some(triple) = args.target() {
         if triple == meta.host {

Run cargo install --path . to install the modified cargo-xbuild

Get a copy of the Rust sources that corresponds to the installed compiler binary, and set up the environment accordingly:

> rustc --version
rustc 1.72.1 (d5c2e9c34 2023-09-13) (built from a source tarball)
> git clone --depth=1 --recurse-submodules --shallow-submodules https://github.com/rust-lang/rust --branch 1.72.1
> export XARGO_RUST_SRC=`pwd`/rust/library

Disable other arbitrary checks in the Rust compiler:

> export RUSTC_BOOTSTRAP=1

And you can now simply run cargo xbuild to build the firmware.