### What needs to get done PR #96 restricted the calls to `dpkg --add-architecture` to only "compatible" pairs of architectures. This suits a lot of use cases, particularly those that just need to download (but not install) packages from a non-host arch. Where this breaks is effective cross-compilation; any non-trivial cross-compilation case will require dependencies in the target architecture (like dev versions of shared libraries), and the common idiom of: ```yaml build-packages: - libxx-dev:arch stage-packages: - libxx:arch ``` does *not* work because the installation of libxx-dev:arch fails, because the target arch there has not been added to the system via `dpkg --add-architecture`. As #96 explains, the reason we can't just call `dpkg --add-architeture non-host-arch` is because the official archives list all archs (even those they don't have packages for) *and* default Apt installations do not restrict the archs in those archives. See `/etc/apt/sources.list` on my machine: ``` ... deb http://archive.ubuntu.com/ubuntu jammy-updates universe ... ``` ... so `apt update` will try to fetch the packages listing for "non-host-arch" from archive.ubuntu.com and fail. What we need to investigate/prototype is a different strategy: if a package-repo with a non-host arch is added (e.g. adding an `armhf` repo in an `amd64` host), we must call `dpkg --add-architecture armhf` (or whatever arch), but we must *also* fix those sources listings that don't "pin" the arch. In the example above, the new line would read: ``` ... deb [arch=amd64] http://archive.ubuntu.com/ubuntu jammy-updates universe ... ``` Here's a series of steps that users are currently doing in host installations to support this scenario: ``` > dpkg --add-architecture ${ARCH} > sed -ri "s/^deb /deb [arch=amd64] /g" /etc/apt/sources.list > apt update > apt --fix-broken install -y > apt upgrade -y ``` ... of course, that script only fixes a single file and doesn't do any verification of pre-existing architectures, so the actual commands need to be improved, but the general idea is this. ### Why it needs to get done To make the build system more robust and improve support for cross-compilation.