Taming the Steam arm64 client (on pmOS)

The Steam client for arm64 architecture has recently emerged online, prompting excitement among users. While it was anticipated that Valve would announce the Steam Frame, a Snapdragon 8 Gen 3 device running SteamOS, the client turned out to be slightly different from the one meant for the Steam Frame. The client currently behaves unexpectedly and attempts to launch a x86_64 runtime by default, even if a global binfmt-emulator is set up for x86_64 binaries.

Moreover, it seems to be an automated build without the necessary modifications for the Steam Frame to function optimally.

After thorough investigation, it was discovered that the Steam client for arm64 handles libraries differently on the host system, making it compatible with certain Proton versions. Users have either compiled Proton for ARM individually or downloaded the depot from Steam and written their own toolmanifest.vdf file. However, a more streamlined approach could be beneficial, allowing users to run any Proton version, including x86_64 versions, with the arm64 client.

Alternatively, if a native Linux version of a game is available, it would be advantageous to run it through FEX.

The Steam client operates within a SteamRT3C container, which is a container runtime employed for the x86_64 beta client. To achieve compatibility, the SteamRT4 runtime was used for the arm64 client. The client is launched through a shell script called _v2-entry-point and runs within a SteamRT4 container. Various components, such as steam-runtime-launcher-service and steam-runtime-launch-client, facilitate the execution of processes on the host system.

The goal was to enable seamless running of this setup on the Ayaneo Pocket S2, a portable Android handheld with the same SoC as the Steam Frame. The device supports postmarketOS, an Alpine-based Linux distribution. The Steam runtime requires GNU libc (glibc), making it challenging to run on musl-based systems like postmarketOS. However, by reimplementing the frontend of the steam-runtime-tools using bubblewrap and adjusting the image accordingly, it was possible to run Steam successfully on the Ayaneo Pocket S2, providing an experience akin to using a Steam Deck.