Rust Cross-Compilation

Purpose

Guide agents through Rust cross-compilation: adding rustup targets, using cross for hermetic Docker-based cross-builds, cargo-zigbuild for zero-setup cross-compilation, .cargo/config.toml configuration, and embedded bare-metal targets.

Triggers

• "How do I cross-compile Rust for ARM/aarch64?"
• "How do I build a Rust binary for a different OS?"
• "How do I use the cross tool for Rust cross-compilation?"
• "How do I build Rust for embedded (no_std) targets?"
• "How do I use cargo-zigbuild?"
• "My cross-compiled Rust binary won't run on the target"

Workflow

1. Add a rustup target

# List installed targets
rustup target list --installed

# List all available targets
rustup target list

# Add a target
rustup target add aarch64-unknown-linux-gnu
rustup target add x86_64-unknown-linux-musl   # static Linux
rustup target add wasm32-unknown-unknown       # WASM
rustup target add thumbv7m-none-eabi          # Cortex-M

# Build for target
cargo build --target aarch64-unknown-linux-gnu --release

2. Common target triples

Target	Use case
x86_64-unknown-linux-gnu	Linux x86-64 (glibc)
x86_64-unknown-linux-musl	Linux x86-64 (musl, static)
aarch64-unknown-linux-gnu	ARM64 Linux (Raspberry Pi 4, AWS Graviton)
aarch64-unknown-linux-musl	ARM64 Linux static
x86_64-pc-windows-gnu	Windows x86-64 (MinGW)
x86_64-pc-windows-msvc	Windows x86-64 (MSVC)
x86_64-apple-darwin	macOS x86-64
aarch64-apple-darwin	macOS Apple Silicon
wasm32-unknown-unknown	WASM (browser)
wasm32-wasi	WASM with WASI
thumbv7m-none-eabi	Cortex-M3 bare metal
thumbv7em-none-eabihf	Cortex-M4/M7 with FPU
riscv32imac-unknown-none-elf	RISC-V 32-bit bare metal

3. cross tool (Docker-based, easiest)

cross uses pre-built Docker images with the correct cross-toolchain:

# Install
cargo install cross

# Build (drop-in replacement for cargo)
cross build --target aarch64-unknown-linux-gnu --release
cross test --target aarch64-unknown-linux-gnu

# Cross.toml — project configuration

# Cross.toml
[target.aarch64-unknown-linux-gnu]
image = "ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main"
pre-build = [
    "apt-get update && apt-get install -y libssl-dev:arm64"
]

[build.env]
passthrough = ["PKG_CONFIG_PATH", "OPENSSL_DIR"]

4. cargo-zigbuild (zero-setup, uses zig cc)

zig cc ships a complete C cross-toolchain — no system cross-compiler needed:

# Install
cargo install cargo-zigbuild
# Also needs zig installed: https://ziglang.org/download/

# Build (no Docker, no system cross-compiler)
cargo zigbuild --target aarch64-unknown-linux-gnu --release
cargo zigbuild --target x86_64-unknown-linux-musl --release

# Target with glibc version (important for compatibility)
cargo zigbuild --target aarch64-unknown-linux-gnu.2.17 --release
# This builds against glibc 2.17 (very compatible)

# Windows from Linux/macOS
cargo zigbuild --target x86_64-pc-windows-gnu --release

cargo-zigbuild advantages over cross:

• No Docker required
• Faster (no container startup)
• Works for most targets out of the box
• Supports precise glibc version targeting

5. .cargo/config.toml for cross targets

# .cargo/config.toml

[target.aarch64-unknown-linux-gnu]
linker = "aarch64-linux-gnu-gcc"    # System cross-linker
# or with zig:
# linker = "zig"
# rustflags = ["-C", "link-arg=cc", "-C", "link-arg=-target", "-C", "link-arg=aarch64-linux-gnu"]

[target.x86_64-unknown-linux-musl]
linker = "x86_64-linux-musl-gcc"
rustflags = ["-C", "target-feature=+crt-static"]

[target.wasm32-unknown-unknown]
runner = "wasmtime"    # Run WASM tests with wasmtime

[target.thumbv7m-none-eabi]
runner = "qemu-arm -cpu cortex-m3"

6. Static binaries with musl

# Add musl target
rustup target add x86_64-unknown-linux-musl

# Build statically linked binary
cargo build --target x86_64-unknown-linux-musl --release

# Verify it's static
file target/x86_64-unknown-linux-musl/release/myapp
# → ELF 64-bit, statically linked, not stripped

# Or with cargo-zigbuild (easier musl)
cargo zigbuild --target x86_64-unknown-linux-musl --release

7. Embedded bare-metal (#[no_std])

# .cargo/config.toml
[build]
target = "thumbv7em-none-eabihf"   # Set default target

[target.'cfg(target_arch = "arm")']
runner = "probe-run --chip STM32F411CE"

// src/main.rs
#![no_std]
#![no_main]

use core::panic::PanicInfo;

#[cortex_m_rt::entry]
fn main() -> ! {
    loop {}
}

#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

# Cargo.toml
[dependencies]
cortex-m = "0.7"
cortex-m-rt = "0.7"

[profile.release]
opt-level = "z"
lto = true
codegen-units = 1
panic = "abort"

cargo build --release  # Uses default target from .cargo/config.toml

For target triple reference and embedded setup details, see references/.

Related skills

• Use skills/rust/rustc-basics for compiler and profile configuration
• Use skills/compilers/cross-gcc for the underlying cross-compiler setup
• Use skills/zig/zig-cross for Zig's native cross-compilation approach
• Use skills/build-systems/cmake when Rust is part of a CMake cross-build