Cross compilation environment for Rust targeting Musl running on ARMv7

Docker Hub: https://hub.docker.com/r/sensorfu/rust-musl-arm/

This image uses rust Docker image and musl-cross-make tool to build the C/C++ cross compilation environment.

Cross compiling Rust

Everything should be set to automatically get cross compiled binaries. However, some Rust crates depend on external libraries which you have to cross compile yourself. See below for how to cross compile C/C++ libraries.

Mandatory Hello World example:

# export USER=root
# cargo new --bin helloworld
     Created binary (application) `helloworld` project
# cd helloworld
# cargo build --release
   Compiling helloworld v0.1.0 (file:///helloworld)
    Finished release [optimized] target(s) in 0.41 secs
# file ./target/armv7-unknown-linux-musleabihf/release/helloworld
./target/armv7-unknown-linux-musleabihf/release/helloworld: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, not stripped

Cross compiling C/C++ libraries

It's possible to use this image to cross compile C/C++ libraries targeting ARMv7 Musl. For autoconf based projects it should be enough to call ./configure script with --host=armv7-linux-musleabihf parameter.

Some environment variables are already set to help with cross compiling C/C++ libraries. See section "Environment variables" below.

For example compiling LibreSSL:

# export LIBRESSL="libressl-2.5.5"
# mkdir work && cd work
# curl -fo- https://ftp.openbsd.org/pub/OpenBSD/LibreSSL/${LIBRESSL}.tar.gz | tar zxf -
# cd ${LIBRESSL}
# ./configure --host=armv7-linux-musleabihf --enable-shared=no && make -j$(nproc)
# file apps/openssl/openssl
apps/openssl/openssl: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-armhf.so.1, not stripped

Environment variables

Inside the image there are various environment variables set:

• CC: Points to ARMv7 GCC C compiler
• CXX: Points to ARMv7 GCC C++ compiler
• LD: Points to ARMv7 GCC linker

Building and uploading the Docker image

1. Fetch musl-cross-make sources into tree: git submodule update --init
2. Build the docker image: docker build -t sensorfu/rust-musl-arm .
3. Push to Docker Hub: docker push sensorfu/rust-musl-arm

Licenses

Rust

Excerpt from https://www.rust-lang.org/en-US/legal.html:

Rust’s code is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses. See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.

musl-cross-make

musl-cross-make doesn't specify license. Individual components installed by musl-cross-make have their own licenses.