Re: [Xen-devel] Relocatable Xen early boot code

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Jun 12, 2015 at 01:08:41PM +0100, Jan Beulich wrote:
> >>> On 12.06.15 at 13:14, <daniel.kiper@xxxxxxxxxx> wrote:
> > Here I do not want to discuss GRUB2 and multiboot2 protocol support details
> > for relocatable images. It is not needed. It is sufficient to know that it
> > is able to put loaded image anywhere in available memory below 4 GiB. Loaded
> > image is informed about its base address according to multiboot2 protocol
> > via
> > special tag. This is new feature not available in upstream GRUB2. I work on
> > upstreaming it in parallel. Relevant patches will be posted together with
> > Xen patches.
>
> Before going into any detail on what you write later on - if this isn't in
> upstream grub2, why can't you do what you want to do first without
> another change needed in the boot loader? In which case, if I'm reading
> this correctly, you wouldn't need our boot code to become relocatable
> either.

multiboot protocol (any version) puts image at address as it requests.
Always, without any exception. So, in our case starting from 1 MiB.
On legacy BIOS platforms it works. However, on EFI platforms it is not
always possible because sometimes some parts of EFI boot/runtime services
live somewhere around 1 MiB. So, first of all we must change multiboot
protocol behavior (in our case version 2 because it is more flexible)
and learn it to relocate images into free memory region. On the other
hand we must learn Xen early boot code to live at different addresses.
We must do all this changes in GRUB2 and in Xen in parallel.

Please check http://lists.xen.org/archives/html/xen-devel/2015-02/msg01257.html
for more details.

Daniel

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