android13/device/google/cuttlefish/multiarch-howto.md

Adjusting APT Sources for Multiarch

The Cuttlefish host Debian packages can also be built and used on an arm64 based system. However, because certain parts of it are still amd64, the APT sources of the system need to be adjusted for multiarch so that package dependencies can be correctly looked up and installed.

For detailed context, see Multiarch HOWTO, and this document will use Ubuntu 21.04 (Hirsute) as an example for making such adjustments.

The basic idea is to first limit the existing APT sources to arm64 only, so that when a new architecture like amd64 is added, APT won't try to fetch packages for the new architecture from the existing repository, as arm64 packages are in "ports", while amd64 ones are in the main repository. So a line in /etc/apt/sources.list such as:

deb http://ports.ubuntu.com/ubuntu-ports hirsute main restricted

would be changed to:

deb [arch=arm64] http://ports.ubuntu.com/ubuntu-ports hirsute main restricted

Next, each line of config like the above will be duplicated and modified into an entry that corresponds to what's in the main repository, with its architecture limited to amd64. For example, for the same line as shown above, a new entry will be added like this:

deb [arch=amd64] http://archive.ubuntu.com/ubuntu hirsute main restricted

The script below might be handy for this task:

#!/bin/bash
cp /etc/apt/sources.list ~/sources.list.bak
(
  (grep ^deb /etc/apt/sources.list | sed 's/deb /deb [arch=arm64] /') && \
  (grep ^deb /etc/apt/sources.list | sed 's/deb /deb [arch=amd64] /g; s/ports\.ubuntu/archive.ubuntu/g; s/ubuntu-ports/ubuntu/g') \
) | tee /tmp/sources.list
mv /tmp/sources.list /etc/apt/sources.list

Note: please run the above script as root, and adjust for differences in Ubuntu releases or location prefixed repositories for faster download (e.g. us.archive.ubuntu.com instead of archive.ubuntu.com).

Finally, add the new architecture and do an APT update with:

sudo dpkg --add-architecture amd64
sudo apt update

Make sure there's no errors or warnings in the output of apt update. To restore the previous APT sources list, use the backup file sources.list.bak saved by the script in your home directory.