# ARMv7 Dynamic Rust Project from Cargo Package

Using this [Dockerfile](../docker/armhf-stretch-crate) one can build a dynamically
linked Rust project from a Cargo package (`.crate` file, a gzipped tarball) that
depends on `libpcap0.8` in a Debian Stretch container targetting ARMv7.

Note that the Dockerfile does a few special things needed to account for the
*target* architecture's development headers:

1. The `armhf` architecture is added before `apt` is updated using `dpkg --add-architecture armhf`
2. Since `libpcap-dev` itself has no `armhf` installation candidate, the specific package `libpcap0.8-dev:armhf` is specified instead

Without these two steps, cross compliation dependent on libraries that differ across architectures is hopeless.

### Container Build

`$ podman build -t crossbuild-armhf -f armhf-stretch-crate`

### Build Example

This assumes `PROJECT_DIR` is set to the path to which this repo was cloned, and that you have
the Rust toolchain installed with `cargo` on your `PATH`.

The project built in this example is [here](./pcap-example/).

```bash
$ mkdir ~/build_dir
$ cd ${PROJECT_DIR}/examples/pcap-example/
$ cargo package --no-verify --allow-dirty
$ cp target/package/pcap-example-0.1.0.crate ~/build_dir/
$ podman run --rm -it e BIN_NAME="pcap-example" \
	-e BIN_VERSION="0.1.0" \
	-v "${HOME}/build_dir:/opt/build:z \
	crossbuild-armhf:latest \
	/opt/build/armhf-stretch-crate.sh

# Build output redacted

$ file build_dir/*_pcap-example
build_dir/armv7-unknown-linux-gnueabihf_pcap-example: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=40ed6d3beeed98797558d4024fbdb468f58abd49, stripped
```