Re: NVRAM emulation issues in QEMU

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 25/03/2022 07:37, John Paul Adrian Glaubitz wrote:

> Hi Mark!
>
> On 3/24/22 16:39, John Paul Adrian Glaubitz wrote:
> > On 3/24/22 15:40, John Paul Adrian Glaubitz wrote:
> > > Are there any plans to improve the NVRAM emulation in QEMU or is there any alternative
> > > command that we should run on QEMU-based systems?
> >
> > OK, the solution is actually as simple as skipping the "nvram" command when running inside
> > a QEMU guest. However, I have no clue how to detect whether it's running on a QEMU-emulated
> > PowerMac or a real one.
>
> I think the solution is much simpler. We just remove the "nvram" command on Power Macintosh,
> it's actually not needed. According to Apple's documentation, OpenFirmware will automatically
> search for an operating system on any of the disks in the system, so there is no need to set
> the boot-device in NVRAM expliclity [1].
>
> In order to verify that, I just set the "boot-device" on my iBook G4 to NULL and can confirm
> that it still boots fine.
>
> root@ibook-g4:~# nvram --print-config=boot-device
> /pci@f4000000/ata-6@d/@0:2,\\:txbi
> root@ibook-g4:~# nvram --update-config boot-device=""
> root@ibook-g4:~# nvram --print-config=boot-device
> root@ibook-g4:~# reboot
> root@ibook-g4:~# Connection to 192.168.178.175 closed by remote host.
> Connection to 192.168.178.175 closed.
> glaubitz@suse-laptop:~> ssh root@192.168.178.175
> Linux ibook-g4 5.16.0-5-powerpc #1 Debian 5.16.14-1 (2022-03-15) ppc
>
> The programs included with the Debian GNU/Linux system are free software;
> the exact distribution terms for each program are described in the
> individual files in /usr/share/doc/*/copyright.
>
> Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
> permitted by applicable law.
> Last login: Fri Mar 25 08:29:21 2022 from 192.168.178.81
> root@ibook-g4:~#
>
> So, I think it should be safe to just remove these two lines required for setting
> the boot-device in NVRAM from the grub-installer script [2][3].
>
> Adrian
>
> > [1] https://opensource.apple.com/source/bless/bless-37/README.BOOTING
> > [2] https://salsa.debian.org/installer-team/grub-installer/-/blob/master/grub-installer#L961
> > [3] https://salsa.debian.org/installer-team/grub-installer/-/blob/master/grub-installer#L968

Hi Adrian,

Thanks for the links. OpenBIOS should work in the same way here in that it scans each 
volume in order until it finds a HFS/HFS+ partition with a blessed file to load and 
execute.

However I suspect the reason the NVRAM is changed is for the case of dual-boot 
machines where the existing MacOS partition is first shrunk and the Linux partitions 
added at the end. In this case without the OF NVRAM boot-device update I'd expect OF 
to always locate and boot MacOS first, instead of loading grub to offer a choice of 
booting either MacOS or Linux.

I should add that my real G4 is set up like this to allow testing various bits of 
pieces against QEMU. However for QEMU I don't ever dual boot since I can simply boot 
either a MacOS or Linux image directly ;)


ATB,

Mark.