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Add cross-compile-freebsd-rust-binary-with-docker
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For a little side project I'm working on I want to be able to produce
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pre-compiled binaries for a variety of platforms, including FreeBSD. With a bit
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of trial and error I have been able to successfully build working FreeBSD
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binaries from a Docker container, without using (slow) emulation/virtual
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machines. This post describes how it works and how to add it to your own Rust
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project.
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I started with [Sandvine's freebsd-cross-build][freebsd-cross-upstream] repo. Which builds
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a Docker image with a cross-compiler that targets FreeBSD. I made a few updates
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and improvements to it:
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* Update from FreeBSD 9 to 12.
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* Base on newer debian9-slim image instead of ubuntu 16.04.
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* Use a multi-stage Docker build.
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* Do all fetching of tarballs inside the container to remove the need to run a
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script on the host.
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* Use the FreeBSD base tarball as the source of headers and libraries instead
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of ISO.
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* Revise the `fix-links` script to automatically discover symlinks that need
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fixing.
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Once I was able to successfully build the cross-compilation toolchain I built a
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second Docker image based on the first that installs Rust, and the
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`x86_64-unknown-freebsd` target. It also sets up a non-privileged user account
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for building a Rust project bind mounted into it.
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Check out the repo at: <https://github.com/wezm/freebsd-cross-build>
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## Building the Images
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I haven't pushed the image to a container registry as I want to do further
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testing and need to work out how to version them sensibly. For now
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you'll need to build them yourself as follows:
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1. `git clone git@github.com:wezm/freebsd-cross-build.git && cd freebsd-cross-build`
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2. `docker build -t freebsd-cross .`
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3. `docker build -f Dockerfile.rust -t freebsd-cross-rust .`
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## Using the Images to Build a FreeBSD Binary
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To use the `freebsd-cross-rust` image in a Rust project here's what you need to
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do (or at least this is how I'm doing it):
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In your project add a `.cargo/config` file for the `x86_64-unknown-freebsd`
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target. This tells cargo what tool to use as the linker.
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```
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[target.x86_64-unknown-freebsd]
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linker = "x86_64-pc-freebsd12-gcc"
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```
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I use Docker volumes to cache the output of previous builds and the cargo
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registry. This prevents cargo from re-downloading the cargo index and
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dependent crates on each build and saves build artifacts across builds,
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speeding up compile times.
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A challenge this introduces is how to get the
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resulting binary out of the volume. For this I use a separate `docker`
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invocation that copies the binary out of the volume into a bind mounted host
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directory.
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_Originally I tried mounting the whole `target` directory into the container
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but this resulted in spurious compilation failures during linking and lots of
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files owned by `root` (I'm aware of [user namespaces] but haven't set it up
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yet)._
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I wrote a shell script to automate this process:
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```language-shell
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#!/bin/sh
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set -e
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mkdir -p target/x86_64-unknown-freebsd
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# NOTE: Assumes the following volumes have been created:
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# - lobsters-freebsd-target
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# - lobsters-freebsd-cargo-registry
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# Build
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sudo docker run --rm -it \
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-v "$(pwd)":/home/rust/code:ro \
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-v lobsters-freebsd-target:/home/rust/code/target \
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-v lobsters-freebsd-cargo-registry:/home/rust/.cargo/registry \
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freebsd-cross-rust build --release --target x86_64-unknown-freebsd
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# Copy binary out of volume into target/x86_64-unknown-freebsd
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sudo docker run --rm -it \
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-v "$(pwd)"/target/x86_64-unknown-freebsd:/home/rust/output \
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-v lobsters-freebsd-target:/home/rust/code/target \
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--entrypoint cp \
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freebsd-cross-rust \
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/home/rust/code/target/x86_64-unknown-freebsd/release/lobsters /home/rust/output
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```
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This is what the script does:
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1. Ensures that the destination directory for the binary exists. Without this,
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docker will create it but it'll be owned by root and the container won't be
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able to write to it.
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2. Runs `cargo build --release --target x86_64-unknown-freebsd` (the leading
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`cargo` is implied by the `ENTRYPOINT` of the image.
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1. The first volume (`-v`) argument bind mounts the source code into the
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container, read-only.
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2. The second `-v` maps the named volume, `lobsters-freebsd-target` into
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the container. This caches the build artifacts.
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3. The last `-v` maps the named volume, `lobsters-freebsd-cargo-registry`
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into the container. This caches the carge index and downloaded crates.
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3. Copies the built binary out of the `lobsters-freebsd-target` volume into the
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local filesystem at `target/x86_64-unknown-freebsd`.
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1. The first `-v` bind mounts the local `target/x86_64-unknown-freebsd`
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directory into the container at `/home/rust/output`.
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2. The second `-v` mounts the `lobsters-freebsd-target` named volume into
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the container at `/home/rust/code/target`.
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3. The `docker run` invocation overrides the default `ENTRYPOINT` with `cp`
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and supplies the source and destination to it, copying from the volume
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into the bind mounted host directory.
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After running the script there is a FreeBSD binary in
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`target/x86_64-unknown-freebsd`. Copying it to a FreeBSD machine for testing
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shows that it does in fact work as expected!
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One last note, this all works because I don't depend on any C libraries in my
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project. If I did, it would be necessary to cross-compile them so that the
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linker could link them when needed.
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Once again, the code is at: <https://github.com/wezm/freebsd-cross-build>.
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<div class="seperator"><hr class="left">✦<hr class="right"></div>
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Previous Post: [My First 3 Weeks of Professional Rust](/technical/2019/03/first-3-weeks-of-professional-rust/)
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[freebsd-cross-upstream]: https://github.com/sandvine/freebsd-cross-build
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[user namespaces]: https://docs.docker.com/engine/security/userns-remap/
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@ -0,0 +1,12 @@
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---
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title: Cross Compiling Rust for FreeBSD With Docker
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extra: How to cross-compile Rust projects for FreeBSD using Docker, without emulation or virtual machines.
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kind: article
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section: technical
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created_at: 2019-03-25 15:45:00.000000000 +11:00
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#updated_at: 2019-03-24T17:28:56+11:00
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keywords:
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- rust
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- freebsd
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- docker
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short_url:
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@ -117,7 +117,7 @@ writing more about our work in the future.
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<div class="seperator"><hr class="left">✦<hr class="right"></div>
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Previous Post: [A Coding Retreat and Getting Embedded Rust Running on a SensorTag](/technical/2019/03/sensortag-embedded-rust-coding-retreat/)
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Next Post: [Cross Compiling Rust for FreeBSD With Docker](/technical/2019/03/cross-compile-freebsd-rust-binary-with-docker/)
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[:make]: https://neovim.io/doc/user/quickfix.html#:make
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[CLion]: https://www.jetbrains.com/clion/
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@ -4,7 +4,7 @@ extra: Reflecting on the first 3 weeks of writing Rust in my new job.
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kind: article
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section: technical
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created_at: 2019-03-24 09:45:00.000000000 +11:00
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updated_at: 2019-03-24T17:28:56+11:00
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updated_at: 2019-03-25T16:08:40+11:00
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keywords:
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- rust
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short_url:
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