linux-kernel - Re: [PATCH 6/7] Add EFI stub for ARM

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Message-ID: <20130806103108.GD2791@e103592.cambridge.arm.com>
Date:	Tue, 6 Aug 2013 11:31:08 +0100
From:	Dave P Martin <Dave.Martin@....com>
To:	Leif Lindholm <leif.lindholm@...aro.org>
Cc:	Roy Franz <roy.franz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH 6/7] Add EFI stub for ARM

On Mon, Aug 05, 2013 at 04:33:19PM +0100, Leif Lindholm wrote:
> On Mon, Aug 05, 2013 at 03:11:49PM +0100, Dave Martin wrote:
> > > diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> > > index 75189f1..4c70b9e 100644
> > > --- a/arch/arm/boot/compressed/head.S
> > > +++ b/arch/arm/boot/compressed/head.S
> > > @@ -122,19 +122,106 @@
> > >  		.arm				@ Always enter in ARM state
> > >  start:
> > >  		.type	start,#function
> > > -		.rept	7
> > > +#ifdef CONFIG_EFI_STUB
> > > +		@ Magic MSDOS signature for PE/COFF + ADD opcode
> > > +		.word	0x62805a4d
> > 
> > What about BE32?
>  
> The ARM bindings for UEFI specify that the processor must be in
> little-endian mode.
> 
> > In that case, the instruction is a coprocessor load, that loads from a
> > random address to a coprocessor that almost certainly doesn't exist.
> > This will probably fault.
> > 
> > Since BE32 is only for older platforms (<v6) and this is not easily
> > solvable, it might be sensible to make the EFI stub support depend on
> > !CPU_ENDIAN_BE32.
>  
> Well, it would make more sense to make EFI_STUB depend on EFI and
> EFI depend on !CPU_ENDIAN_BE32. Which is something I can add to
> my next set of general ARM UEFI patches. Thanks.

That sounds fair enough.

Cheers
---Dave
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