How to use the new Redox cross compile support

redox_cross.sh

# Clone Rust with Redox cross compilation support
git clone https://github.com/redox-os/rust -b redox_cross --recursive

# Make a build directory
cd rust
mkdir build
cd build

# Create a config.toml
cat > config.toml <<EOF
[build]
target = ["x86_64-unknown-redox"]
[rust]
codegen-units = 0
use-jemalloc = false
EOF

# Build Rust
../x.py build -j$(nproc) --stage 1

# Stage Rust
../x.py dist -j$(nproc) --keep-stage 1

# Install Rust
build/tmp/dist/rustc-1.15.0-dev-x86_64-unknown-linux-gnu/install.sh --prefix=`pwd`/prefix --verbose
build/tmp/dist/rust-std-1.15.0-dev-x86_64-unknown-linux-gnu/install.sh --prefix=`pwd`/prefix --verbose
build/tmp/dist/rust-std-1.15.0-dev-x86_64-unknown-redox/install.sh --prefix=`pwd`/prefix --verbose

# Build and install openlibm
git clone https://github.com/redox-os/openlibm.git -b master
CFLAGS=-fno-stack-protector make -C openlibm libopenlibm.a
cp openlibm/libopenlibm.a prefix/lib/rustlib/x86_64-unknown-redox/lib

# Build and install syscall crate
git clone https://github.com/redox-os/syscall.git -b master
prefix/bin/rustc syscall/src/lib.rs --target=x86_64-unknown-redox --crate-type rlib --crate-name syscall --out-dir prefix/lib/rustlib/x86_64-unknown-redox/lib

# Build and install ralloc crate
git clone https://github.com/redox-os/ralloc.git -b redox_cross
prefix/bin/rustc ralloc/src/lib.rs --target=x86_64-unknown-redox --crate-type rlib --crate-name ralloc --cfg 'feature="allocator"' --out-dir prefix/lib/rustlib/x86_64-unknown-redox/lib

# Create and build a test application
cat > test.rs <<EOF
fn main() {
    println!("Hello from Redox");
}
EOF
prefix/bin/rustc --target=x86_64-unknown-redox test.rs

# Install on Redox
REDOX_PATH=../../redox
cp test "$REDOX_PATH/filesystem/bin"
cd "$REDOX_PATH"
make qemu

# Test in Redox - expected output "Hello from Redox"
test