Cross compiling Rust -- Fixed

Set up rust build environment

rustup toolchain install nightly
rustup component add rust-src --toolchain nightly
apt install {binutils,gcc}-mips-linux-gnu

Choose glibc or musl as your libc

You can use glibc, but it’s not worked as well for me as using musl. I got some missing symbols when trying this on larger programs with glibc. So I recommend using musl.

mips-unknown-linux-musl is with musl libc, and mips-unknown-linux-gnu is glibc.

Optional: Set up for glibc

I needed to create a special target for glibc, to turn on soft-float. soft-float seems on by default in mips-unknown-linux-musl.

rustc +nightly \
    -Z unstable-options \
    --print target-spec-json \
    --target mips-unknown-linux-gnu \
    > mips-nofloat-linux-gnu.json

Then edit mips-nofloat-linux-gnu.json

Change is-builtin to false
add +soft-float to features list.

Create test project

cargo new foo
cd foo

Configure linker

mkdir .cargo
cat > .cargo/config.toml
[target.'cfg(target_arch="mips")']
linker = "mips-linux-gnu-gcc"
^D

Build

Using musl (worked better for me):

cargo +nightly build --release -Zbuild-std --target mips-unknown-linux-musl.json

Using glibc (requires the optional step above):

cargo +nightly build --release -Zbuild-std --target mips-nofloat-linux-gnu.json

Change the “interpreter” to what the Ubiquiti system expects

cd target/mips-unknown-linux-musl/release  # or -gnu, if using glibc
patchelf \
    --remove-needed ld.so.1 \
    --set-interpreter /lib/ld-musl-mips-sf.so.1 \
    foo

Does it work?

$ ./foo
Hello, world!

Yay!