linux-kernel - Re: RFC: default CONFIG_EFI

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Message-ID: <1376420525.3467.70.camel@dabdike.int.hansenpartnership.com>
Date:	Tue, 13 Aug 2013 12:02:05 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: RFC: default CONFIG_EFI_STUB=y

On Tue, 2013-08-13 at 11:52 -0700, H. Peter Anvin wrote:
> On 08/13/2013 11:43 AM, James Bottomley wrote:
> > Can we actually boot a 32 bit kernel on an EFI64 system?  The last time
> > I tried on my Secure Boot SDV it wouldn't work; the problem is getting
> > someting in the transfer of control path to boot the processor back to
> > 32 bit mode.
> 
> We can boot with a bootloader in "skip stub" mode; no runtime services
> yet.

So the bootloader has to do the 64->32 transition?

>   We are working on making it possible to boot via a EFI stub in
> assisted mode (still needing a bootloader, but with the boot stub in the
> kernel.)
> 
> Runtime services will be the last piece, obviously, but even that looks
> reasonably doable.

So why not start with the working case (default to EFI on 64 bit) and
add in the mostly non-working case (default to EFI on 32 bit) when it
actually mostly works?

James


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