linux-kernel - Re: [PATCH v2 10/10] x86, efi: EFI boot stub support

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Date:	Tue, 13 Sep 2011 16:33:05 +0200
From:	Maarten Lankhorst <m.b.lankhorst@...il.com>
To:	Matt Fleming <matt@...sole-pimps.org>
CC:	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Matthew Garrett <mjg@...hat.com>, x86@...nel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matt Fleming <matt.fleming@...el.com>,
	Mike Waychison <mikew@...gle.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v2 10/10] x86, efi: EFI boot stub support

Hey Matt,

On 09/12/2011 04:34 PM, Matt Fleming wrote:
> From: Matt Fleming <matt.fleming@...el.com>
>
> There is currently a large divide between kernel development and the
> development of EFI boot loaders. The idea behind this patch is to give
> the kernel developers full control over the EFI boot process. As
> H. Peter Anvin put it,
>
> "The 'kernel carries its own stub' approach been very successful in
> dealing with BIOS, and would make a lot of sense to me for EFI as
> well."
>
> This patch introduces an EFI boot stub that allows an x86 bzImage to
> be loaded and executed by EFI firmware. The bzImage appears to the
> firmware as an EFI application. Luckily there are enough free bits
> within the bzImage header so that it can masquerade as an EFI
> application, thereby coercing the EFI firmware into loading it and
> jumping to its entry point. The beauty of this masquerading approach
> is that both BIOS and EFI boot loaders can still load and run the same
> bzImage, thereby allowing a single kernel image to work in any boot
> environment.
>
> The EFI boot stub supports multiple initrds, but they must exist on
> the same partition as the bzImage. Command-line arguments for the
> kernel can be appended after the bzImage name when run from the EFI
> shell, e.g.
>
> Shell> bzImage console=ttyS0 root=/dev/sdb initrd=initrd.img
>
> Cc: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Mike Waychison <mikew@...gle.com>
> Cc: Matthew Garrett <mjg@...hat.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Maarten Lankhorst <m.b.lankhorst@...il.com>
> Signed-off-by: Matt Fleming <matt.fleming@...el.com>
> ---
>
> v2:
>  - File alignment was too large, was 8192 should be 512. Reported by
>    Maarten Lankhorst.
>  - Added UGA support for graphics
>  - Use VIDEO_TYPE_EFI instead of hard-coded number.
>  - Move linelength assignment until after we've assigned depth
>  - Dynamically fill out AddressOfEntryPoint in tools/build.c
>  - Don't use magic number for GDT/TSS stuff. Requested by Andi Kleen
>  - The bzImage may need to be relocated as it may have been loaded at
>    a high address address by the firmware. This was required to get my
>    macbook booting because the firmware loaded it at 0x7cxxxxxx, which
>    triggers this error in decompress_kernel(),
>
> 	if (heap > ((-__PAGE_OFFSET-(128<<20)-1) & 0x7fffffff))
> 		error("Destination address too large");
>
This version seems to boot for me. Is it useful to add 32-bits support though?
It seems that only some older versions of OSX use it. I could see if I can
revive my mac mini, iirc it has 32-bits efi, or at least used to have.

Do I need to pass anything to add it to efibootmgr?

I tried something like this:
echo "args" | efibootmgr -c -l '\vmlinuz.efi' -L 'Native EFI linux boot' -@ - -u -d /dev/sdb

And it boots vmlinuz.efi, but the arguments I passed do not appear to have any effect.

~Maarten

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