linux-kernel - Re: [PATCH 1/3] arm64: add EFI stub

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Message-ID: <1386336870.1861.155.camel@deneb.redhat.com>
Date:	Fri, 06 Dec 2013 08:34:30 -0500
From:	Mark Salter <msalter@...hat.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	"roy.franz@...aro.org" <roy.franz@...aro.org>
Subject: Re: [PATCH 1/3] arm64: add EFI stub

On Fri, 2013-12-06 at 12:25 +0000, Grant Likely wrote:
> On Thu, 5 Dec 2013 15:28:06 +0000, Catalin Marinas <catalin.marinas@....com> wrote:
> > On Thu, Dec 05, 2013 at 02:43:23PM +0000, Mark Salter wrote:
> > > On Thu, 2013-12-05 at 14:18 +0000, Catalin Marinas wrote:
> > > > On Fri, Nov 29, 2013 at 10:05:10PM +0000, Mark Salter wrote:
> > > > > This patch adds PE/COFF header fields to the start of the Image
> > > > > so that it appears as an EFI application to EFI firmware. An EFI
> > > > > stub is included to allow direct booting of the kernel Image. Due
> > > > > to EFI firmware limitations, only little endian kernels with 4K
> > > > > page sizes are supported at this time.
> > > > 
> > > > I don't fully understand the EFI firmware limitations but for big endian
> > > > we could have the EFI_STUB wrapper in little endian and get the kernel
> > > > to switch to big endian once booted. The image header should always be
> > > > little endian.
> > > 
> > > That would be fun. :) You'd also have to switch back and forth to make
> > > EFI runtime services calls.
> > 
> > OK, we'll have to live with this restriction.
> 
> Or just disable runtime services on the switch to big ending. Big endian
> should not disable the stub (but getting it to work could be a follow-up
> patch)
> 
The other problem with BE is that the PE/COFF masquerading is built into
head.S so the same Image can be used for EFI and non-EFI. I don't see
a BE opcode which we could us to provide the magic "MZ" at the start
of a BE kernel Image.

--Mark


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