I've found a number of how-tos on the net about cross-compiling for the Raspberry Pi. None of them worked as the compile targets/tools were wrong. Here's what worked for me. The target boxes in this case are running 64 bit versions of Ubuntu 22.04.

I'm doing all the building on Ubuntu 22.04 x86_64

The target you are wanting to install is aarch64-unknown-linux-gnu.

rustup target add aarch64-unknown-linux-gnu

You'll actually need to install the appropriate build tools, specifically for the linking portion of the build.

sudo apt install g++-12-aarch64-linux-gnu

In the root of your Rust project you want to build (where your Cargo.toml file is), do the following:

# You have to create a build config with the linker set appropriately
mkdir .cargo
cat <<"EOF" > .cargo/config.toml
[build]
 
[target.aarch64-unknown-linux-gnu]
linker = "aarch64-linux-gnu-g++-12"
EOF
 
# Now you can build!
cargo build --release --target aarch64-unknown-linux-gnu