Re: [Qemu-devel] [PATCH 0/4] Add multiboot support (x86) v2

["François Revol" <revol@free.fr>]

> François Revol schrieb:
> >> Why would an OS want to parse multiboot structures but not
> > > implement
> >> proper multiboot support? I mean, this really isn't anything
> >> complicated. When you have enabled it to understand multiboot
> >> structures
> >> you are only missing a handful of bytes for the multiboot header.
> >>
> >> What is it that you need to do differently for Haiku?
> >
> > Because Haiku has its own second stage loader, which requires the
> > BIOS
> > to locate the kernel and module in a BFS partition which grub
> > doesn't
> > implement btw.
>
> That makes sense on real hardware, of course. But for -kernel you
> don't
> need a file system to read the kernel from.

Except that wouldn't be the actual kernel passed but the 2nd stage.
And having to pass the kernel in a tgz outside the BFS image makes it
more complex to set up.

> I'm not talking about replacing the existing loader, but just about
> adding support for multiboot as an additional option. Don't know how
> the
> Haiku boot process works though, so maybe I'm completely wrong.

Yes that's possible, we already support OF for PPC, and we'll implement
U-Boot support for ARM anyway.
It's just that I "just" needed to pass args for this usage.

> > It also handles PM switching by itself.
> > Haiku might also use the BIOS for other stuff, like VESA mode
> > switching, so I'd need to make sure all calls aren't strictly
> > required.
>
> In theory you could switch back to Real Mode when starting through
> multiboot and then continue as with a normal boot. Admittedly,
> doesn't
> sound exactly nice, but should be doable...

The loader can likey detect it anyway. If multiboot is used it should't
need to call the BIOS to read the kernel anyway. It's just a different
code path.
PPC boot starts with paging enabled IIRC.

François.