Re: KGDB on virt68k?

[Chris Hanson <cmhanson%eschatologist.net@localhost>]

On Apr 27, 2026, at 3:56 PM, Jason Thorpe <thorpej%me.com@localhost> wrote:
> So maybe VirtIO serial might be a better approach for KGDB. (I assume if I create an appropriate node in /dev and run getty on it that I'd be able to connect to that port and get a login...)
> 
> Yah, should:
> 
> device-major viocon    char 364            viocon

So, I tried this, but it appears that VirtIO serial/console on NetBSD isn’t yet ready for prime time. Looks like this is noted in BUGS in the viocon(4) man page:

     Use as a kernel console for NetBSD is not yet supported.

     The multiport feature is not yet supported.

So I built a QEMU with a tweaked hw/m68k/virt.c that provides four Goldfish TTYs 0x200 bytes apart, a tweaked NetBSD that expects the same (there doesn’t appear to be a way to pass the count or stride of the Goldfish TTY devices, only one of which is passed in the Linux bootinfo), and then configured the appropriate devices after booting a newly-generated live image and that Just Worked.

That makes me wonder whether it’d be a better investment of my time to get Goldfish TTY usable by KGDB or to get viocon(4) working and usable by KGDB. It doesn’t seem like switching QEMU virt68k to support VirtIO console would be verry difficult, and it already allows attaching any number of them (all of which NetBSD will at least already detect, even if they don’t currently work).

  -- Chris