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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 05 Oct 2015 11:18:41 +0200
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Subject: Re: [Qemu-devel] [PATCH v4 6/7] Make the kernel image in the fw_cfg
 DMA interface bootable
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To: Kevin O'Connor <kevin@koconnor.net>
Cc: Drew <drjones@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Marc =?ISO-8859-1?Q?Mar=ED?= <markmb@redhat.com>, Laszlo Ersek <lersek@redhat.com>

On Fr, 2015-10-02 at 09:38 -0400, Kevin O'Connor wrote:
> On Fri, Oct 02, 2015 at 10:16:26AM +0200, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > > That's fine with me.  Marc - I think qemu_vmlinux_setup() in SeaBIOS
> > > with the following would work:
> > > 
> > > void qemu_vmlinux_setup(void)
> > > {
> > >     u32 kernel_size;
> > >     qemu_cfg_read_entry(&kernel_size, QEMU_CFG_KERNEL_SIZE, sizeof(kernel_size));
> > >     if (kernel_size)
> > >         boot_add_qemu_vmlinux("QEMU Kernel image", 0);
> > > }
> > 
> > It isn't that simple.  We also have support for multiboot kernels (using
> > multiboot.bin option rom).  So when doing this you need to be prepared
> > to find a multiboot kernel in fw_cfg.
> 
> Is there some way to detect if it's a multiboot kernel?

Yes.  There is a header with magic + checksum in the first 8k, see
hw/i386/multiboot.c (in qemu).

Or check the option rom name in the bootorder file, it's multiboot
instead of linuxboot.

>   If so,
> seabios can just fall back to using multiboot.bin.

Or add multiboot support to seabios.

cheers,
  Gerd