Define PKG_CONFIG_PATH in Docker images

[gdesmott]

As stated on #149 (comment) one has to manually define PKG_CONFIG_PATH in their custom docker image in order to build Rust code relying on external libs.

Automatically defining it in the cross images would make things easier as users would just have to derive from the official images and install their extra packages.
Would you consider such change in the docker files?

[capnfabs]

I just ran into this and agree that changing the docker images for this would be helpful. The fact that cross sets PKG_CONFIG_ALLOW_CROSS=1 in the env for the build without changing the path, set me up to make a mistake when building my own container: I installed both the host + target arch for a given lib, and then pkg-config picked the host arch.

In the end, my solution was to set PKG_CONFIG_LIBDIR in the Dockerfile, as per this article, so my Dockerfile now looks like this:

FROM rustembedded/cross:armv7-unknown-linux-gnueabihf-0.2.1

RUN dpkg --add-architecture armhf

RUN apt-get update && \
    apt-get install --assume-yes libasound2-dev:armhf libssl-dev:armhf

ENV PKG_CONFIG_LIBDIR=/usr/local/lib/arm-linux-gnueabihf/pkgconfig:/usr/lib/arm-linux-gnueabihf/pkgconfig

The advantage of PKG_CONFIG_LIBDIR over PKG_CONFIG_PATH is that it overrides what pkg-config selects by default, which means you can't accidentally link the host architecture version of something if you forget to install the target arch package.

[Crell]

This seems to be causing issues with rust-openssl as well. I don't know the guts of Cross well enough to say what may be going on or how to fix it, but I can confirm the problem still exists.

[capnfabs]

@Crell in case it's helpful to you (and others!), I kept digging into this after I left that comment, and have written a couple of in-depth blog posts about getting cross-compile working with system packages, they're here:

• Cross-Compiling Rust apps for the Raspberry Pi -- describes building a custom container using the approach in my comment, above (but improved a little)
• Cross-Compiling Rust Apps II: Linux Subtrees and Linker Shenanigans -- describes building a custom container which has a target linux distribution in a subdirectory of the container's filesystem.

[zwhitchcox]

Is there a workaround?

[zwhitchcox]

I don't have the directory /usr/local/lib/arm-linux-gnueabihf/pkgconfig on my local computer

[zwhitchcox]

Ok, I'm able to buidl using the Dockerfile from @capnfabs

[zwhitchcox]

Was able to get this to work in the docker file.

Here's my file for aarch64 in case it helps anyone:

FROM rustembedded/cross:aarch64-unknown-linux-gnu-0.2.1

WORKDIR /home/src

RUN dpkg --add-architecture arm64

RUN apt-get update && \
    apt-get install --assume-yes libssl-dev:arm64

ENV PKG_CONFIG_LIBDIR=/usr/lib/aarch64-linux-gnu/pkgconfig

RUN curl https://sh.rustup.rs -sSf | \
    sh -s -- --default-toolchain stable -y

ENV PATH=/root/.cargo/bin:$PATH

RUN apt-get install libssl-dev pkg-config -y

COPY . .

CMD cargo build --release