Comment 3 for bug 1775249

So, what happened is that with seabios 1.11.1-1 a serial console has been implemented and enabled by default, redirecting all VGA output (SERCON is by default y). There was no such thing before and this is now causing issues. It would be unwise to try and change the default, as we would introduce a delta against Debian. There's a workaround we can use which solves the problem.

The grub2 test suite relies on serial output as this is how grub-shell communicates with the tests being run. Thankfully, seabios has support for runtime configuration, which is done through the fw_cfg interface in qemu. Passing "-fw_cfg name=etc/sercon-port,string=0" to the qemu-system-* calls in grub-shell forces seabios to use a different port for its own output, therefore not interfering with what is used by grub. There's an additional warning printed out, but it doesn't seem to interfere with the actual tests.

I am currently test-building that to make sure it's enough to make grub2 buildable again. If yes, I will release it to cosmic and then forward to Debian - as they're also affected by the same change.