Update 27 November 2019: a new 1.5.2 release of the image is available; please see this post for more details.
If you have an RPi4, and would like to try running under it under a 64-bit (kernel+userland) OS (whether for comparative benchmarking, access to aarch64-only packages, or just out of curiosity), you might like to check out my recently released gentoo-on-rpi-64bit bootable image (downloadable from GitHub, here).
Here's a screenshot of the 64-bit image running on a dual-display RPi4 B (click to show a higher resolution view):
You can burn the image (~1,643MiB compressed) to a microSD card (>=16GB) (either from the command line, or using a GUI tool like Etcher), then boot your RPi4B (RPi3B/B+ also supported) from it directly (the root partition will be automatically resized to fill the card on first boot). Full instructions for download and use are provided on the project's GitHub page.
Although this is Gentoo, the image boots - without configuration - to an Xfce4 desktop, so it is easy to start it up and play around with it.
It also comes bundled with a reasonable set of pre-installed aarch64 packages (LibreOffice v188.8.131.52, Firefox Quantum v68.0.1, Chromium v76.0.3809.87, Thunderbird v60.8.0, VLC v184.108.40.206, Kodi v18.0, GIMP v2.10.12 etc.) so that you can get productive without having to compile anything first! Unless you want to, of course; this being Gentoo, GCC v9.1.0, Clang v8.0.1, IcedTea v3.13.0 (OpenJDK 8), Go v1.12.7, Rust v1.36.0 and various versions of Python are of course bundled also ^-^
Thanks to rapid upstream progress on aarch64 kernel work for the new board, there are surprisingly few compromises required when running the Pi4 under a 'pure' 64-bit OS such as this one. Specifically, for the Pi4 in this 1.5.0 release:
- V3D graphics acceleration is supported in X under vc4-fkms-v3d / Mesa;
- the full 4GiB complement of memory is usable (if you are lucky enough to own a top-of-the-line model, that is ^-^);
- the V4L2 M2M video codecs and optional plug-in camera module are both usable;
- use of dual HDMI displays is supported;
- Bluetooth, fast Ethernet, and dual-band WiFi work.
Have fun ^-^