[gentoo-user] Serial console stops working as soon as openrc starts

[Grant Edwards <grant.b.edwards@gmail.com>]

I've set up a serial console by adding the following to my kernel
command line:

    console=ttyS0,115200 console=tty1

It works fine for the first few seconds as the kernel starts up. All
of the expected messages are sent out ttyS0.

But, soon after init starts, the serial console stops working.

The end of the serial console log always looks like this

[    3.502684] Freeing unused kernel image (initmem) memory: 1516K
[    3.509155] Write protecting the kernel read-only data: 24576k
[    3.515861] Freeing unused kernel image (text/rodata gap) memory: 2036K
[    3.523160] Freeing unused kernel image (rodata/data gap) memory: 1156K
[    3.568699] x86/mm: Checked W+X mappings: passed, no W+X pages found.
[    3.575655] x86/mm: Checking user space page tables
[    3.615655] x86/mm: Checked W+X mappings: passed, no W+X pages found.
[    3.622604] Run /sbin/init as init process
[    3.660655] kbd_mode (115) used greatest stack depth: 13096 bytes left
[    3.667760] loadkeys (116) used greatest stack depth: 13048 bytes left

On the tty1 console, the next thing after the "loadkeys" line above is
the OpenRC banner, so apparently openrc is messing with my console
settings.  It's been a few years since I setup a serial console, but
after adding the "console=" argument to the kernel args it used to
"just work".

How do I get openrc to leave the serial console alone?

--
Grant