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Re: EFI and multiboot2 devlopment work for Xen

From: Konrad Rzeszutek Wilk
Subject: Re: EFI and multiboot2 devlopment work for Xen
Date: Tue, 22 Oct 2013 10:51:40 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Oct 22, 2013 at 03:24:28PM +0100, Ian Campbell wrote:
> On Tue, 2013-10-22 at 10:09 -0400, Konrad Rzeszutek Wilk wrote:
> > So it can be booted the same way as xen.efi. But my understanding is
> > that folks prefer a bootloader instead of loading the bzImage in an
> > NVRAM of a platform with pre-set parameters. Hence that mechanism
> > is not used by the majority of users.
> My understanding is that they prefer a bootloader which can launch Linux
> as a PE/COFF image, i.e. the linuxefi thing.
> > Instead the majority of users would like to use a bootloader, like
> > GRUB2. And there are certain restrictions - if you launch from it
> > an PE/COFF application GRUB2 will call ExitBootServices. But if
> > you launch the Linux image (so using the linuxefi), it WILL NOT
> > call ExitBootServices.
> "linuxefi" won't call ExitBootServices but it will launch as a PE/COFF
> application not as a "Linux image", that's right isn't it? I think that
> is the whole point of it.

No. The linuxefi will parse the payload and verify that it has the
Linux x86/boot protocol. So any PE/COFF image won't do.
(See grub_cmd_linux in grub-core/loader/i386/efi/linux.c)

If you use 'linux' module, it will call ExitBootService.
If you use 'multiboot' module, it will call ExitBootService too.

So if you don't want to the module to call 'grub_efi_finish_boot_services'
you need to use 'linuxefi' :-)

And I still haven't found the module that can launch any PE/COFF
image from GRUB2. Maybe that is a myth.
> The "launch as a Linux image" grub command is called just "linux" (and
> "kernel" may be a synonym).
> > But I say that (about ExitBootServices) - and I can't find it in
> > the GRUB2 code, so perhaps I am mistaken.
> linuxefi isn't in the upstream grub2 tree -- all the distros are
> carrying it as a patch. So if you are grepping upstream you won't find
> it.

Right, I am looking at Fedora 19's GRUB2 sources.
> Ian.

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