So I compiled the sun7i legacy kernel without any modifications, but it won't boot. This does not make sense to me, as it should be the same that is being downloaded. The net upgrade size is -0.02 MiB.
The kernel loads, the LEDs blink, but they show a very low load only a second after booting, so obviously something is stopping the boot. The HDMI monitor says 'Input not supported'. The network is not connected. Journald does not log. Again, with the downloaded sun7i kernel all of this works fine.