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Re: [Xen-devel] Is: Wrap-up Was: Re: EFI and multiboot2 devlopment work for Xen

On Mon, Nov 04, 2013 at 08:41:11PM +0000, Stefano Stabellini wrote:
> > 
> > multiboot2 protocol requires some more changes. However, about 80% of code
> > is ready. In this case Xen and modules are loaded by GRUB2 itself. It means
> > that all images could be placed on any filesystem recognized by GRUB2. 
> > Options
> > for Xen and modules are passed separately which simplifies command line 
> > editing
> > in boot loader and parsing. multiboot2 protocol is very flexible and could 
> > be
> > easily extended in the future if a need arises. Support for secure boot and
> > shim loader could be added. However, it was not implemented yet. Probably
> > linuxefi module could be used as a reference or even as a base for 
> > development.
> > However, I do not know are there plans to support such solution by GRUB2
> > community. Currently, support for native PE images signatures and GPG 
> > signatures
> > is under development for GRUB2 upstream.
> FYI on ARM it is possible to load a kernel as PE but at the same time
> passing additional info as where the initrd or other additional binaries
> have been loaded or even command line arguments. These info are passed
> from the bootloader to the kernel via Device Tree.  Grant (CC'ed) might
> be able to add additional details on where the code actually lives.
The code currently lives in unclean form in my development tree on
git.linaro.org. We had a few items on the kernel boot protocol to sort
out at last week's Linaro Connect, and if I hadn't been struck down
with conference flu, I would probably have sent out the basic arm64
support by now.

The method used (for the curious) is to simply register an FDT as a
configuration table, and then look for that in the stub.

That code should be trivially portable to 32-bit ARM.

I did start out from the linuxefi code, but that was quite x86 specific,
and was also dependent on the shim, so I ended up changing most of it
(for now). I would still like to see a unified (upstream) linuxefi
module for loading the kernel as the UEFI stub
(with architecture-specific bits extracted out under loader/<arch>).

The UEFI stub loader will then call ExitBootServices(), not GRUB.


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