Building 32-bit xen.efi for 32-bit EFI platforms

Building 32-bit xen.efi for 32-bit EFI platforms

[Zhuan Chen]

Hi,

I am wondering whether it's possible to build 32-bit xen.efi for the
32-bit EFI platform? One way of building xen.efi I learnt is to make
the binutils configured with the x86_64-pep emulation (according to
the document http://xenbits.xenproject.org/docs/unstable/misc/efi.html).
The resulted xen.efi is 64-bit mode. Is it possible to build xen.efi
as the 32-bit mode?

The reason for this question is due to my effort of installing Xen on
the Asus Transformer Book T100, which is one of the Bay Trail Atom
(64-bit processors) tablets shipped with 32-bit EFI firmware. This
requires the support of the 32-bit EFI bootloader. Such platforms seem
to become common and Linux kernel from 3.15 also provides the EFI
mixed mode to support 64-bit kernels running from 32-bit EFI firmware.

Thanks,
Zhuan

Re: Building 32-bit xen.efi for 32-bit EFI platforms

[Andrew Cooper]

On 24/11/14 14:59, Zhuan Chen wrote:
> Hi,
>
> I am wondering whether it's possible to build 32-bit xen.efi for the
> 32-bit EFI platform? One way of building xen.efi I learnt is to make
> the binutils configured with the x86_64-pep emulation (according to
> the document http://xenbits.xenproject.org/docs/unstable/misc/efi.html).
> The resulted xen.efi is 64-bit mode. Is it possible to build xen.efi
> as the 32-bit mode?
>
> The reason for this question is due to my effort of installing Xen on
> the Asus Transformer Book T100, which is one of the Bay Trail Atom
> (64-bit processors) tablets shipped with 32-bit EFI firmware. This
> requires the support of the 32-bit EFI bootloader. Such platforms seem
> to become common and Linux kernel from 3.15 also provides the EFI
> mixed mode to support 64-bit kernels running from 32-bit EFI firmware.
>
> Thanks,
> Zhuan

32bit Xen support was removed in Xen 4.3, so building a pure 32bit
hypervisor is not possible.

There is an argument to be made for building a 32bit Xen.efi which is
bootable by a 32bit firmware and moves into 64bit mode on boot.

There is however no support for this that I am aware of.

~Andrew

Re: Building 32-bit xen.efi for 32-bit EFI platforms

[Ian Campbell]

On Mon, 2014-11-24 at 15:09 +0000, Andrew Cooper wrote:
> On 24/11/14 14:59, Zhuan Chen wrote:
> > Hi,
> >
> > I am wondering whether it's possible to build 32-bit xen.efi for the
> > 32-bit EFI platform? One way of building xen.efi I learnt is to make
> > the binutils configured with the x86_64-pep emulation (according to
> > the document http://xenbits.xenproject.org/docs/unstable/misc/efi.html).
> > The resulted xen.efi is 64-bit mode. Is it possible to build xen.efi
> > as the 32-bit mode?
> >
> > The reason for this question is due to my effort of installing Xen on
> > the Asus Transformer Book T100, which is one of the Bay Trail Atom
> > (64-bit processors) tablets shipped with 32-bit EFI firmware. This
> > requires the support of the 32-bit EFI bootloader. Such platforms seem
> > to become common and Linux kernel from 3.15 also provides the EFI
> > mixed mode to support 64-bit kernels running from 32-bit EFI firmware.
> >
> > Thanks,
> > Zhuan
> 
> 32bit Xen support was removed in Xen 4.3, so building a pure 32bit
> hypervisor is not possible.

That's not what was asked for.

> There is an argument to be made for building a 32bit Xen.efi which is
> bootable by a 32bit firmware and moves into 64bit mode on boot.

This was.

> There is however no support for this that I am aware of.

Me neither.

Ian.

Re: Building 32-bit xen.efi for 32-bit EFI platforms

[Jan Beulich]

>>> On 24.11.14 at 15:59, <zhuanchen@gmail.com> wrote:
> I am wondering whether it's possible to build 32-bit xen.efi for the
> 32-bit EFI platform? One way of building xen.efi I learnt is to make
> the binutils configured with the x86_64-pep emulation (according to
> the document http://xenbits.xenproject.org/docs/unstable/misc/efi.html).
> The resulted xen.efi is 64-bit mode. Is it possible to build xen.efi
> as the 32-bit mode?
> 
> The reason for this question is due to my effort of installing Xen on
> the Asus Transformer Book T100, which is one of the Bay Trail Atom
> (64-bit processors) tablets shipped with 32-bit EFI firmware. This
> requires the support of the 32-bit EFI bootloader. Such platforms seem
> to become common and Linux kernel from 3.15 also provides the EFI
> mixed mode to support 64-bit kernels running from 32-bit EFI firmware.

This mixed mode support is kind of crippled, as it suppresses all use
of runtime services. But that aside, as others said what you ask for
is currently not possible - feel free to submit patches to improve the
situation, but be aware that a number of assumptions of being 64-bit
are currently made in the boot loader code, so you'd have to do
careful code review first to spot all places needing adjustment.

Jan

Re: Building 32-bit xen.efi for 32-bit EFI platforms

[David Vrabel]

On 24/11/14 14:59, Zhuan Chen wrote:
> Hi,
> 
> I am wondering whether it's possible to build 32-bit xen.efi for the
> 32-bit EFI platform? One way of building xen.efi I learnt is to make
> the binutils configured with the x86_64-pep emulation (according to
> the document http://xenbits.xenproject.org/docs/unstable/misc/efi.html).
> The resulted xen.efi is 64-bit mode. Is it possible to build xen.efi
> as the 32-bit mode?
> 
> The reason for this question is due to my effort of installing Xen on
> the Asus Transformer Book T100, which is one of the Bay Trail Atom
> (64-bit processors) tablets shipped with 32-bit EFI firmware. This
> requires the support of the 32-bit EFI bootloader. Such platforms seem
> to become common and Linux kernel from 3.15 also provides the EFI
> mixed mode to support 64-bit kernels running from 32-bit EFI firmware.

You may want to look at using another bootloader (such as grub 2) to
chainload Xen.

Daniel Kiper has the necessary patches to Xen to make this work
(although I've only tried it with 64-bit grub 2).

David