linux-kernel - Re: [PATCH] arm/tegra: select AUTO

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Message-ID: <1318692552.2241.47.camel@computer2>
Date:	Sat, 15 Oct 2011 16:29:12 +0100
From:	Tixy <tixy@...t.co.uk>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Stephen Warren <swarren@...dia.com>,
	Erik Gilling <konkers@...roid.com>,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nico@...xnic.net>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"Colin Cross (ccross@...roid.com)" <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm/tegra: select AUTO_ZRELADDR by default

On Fri, 2011-10-14 at 21:19 +0100, Russell King - ARM Linux wrote:
> On Fri, Oct 14, 2011 at 01:16:27PM -0700, Stephen Warren wrote:
> > Russell King wrote at Friday, October 14, 2011 2:12 PM:
> > > I don't think that's so with the various flavours of platform specific
> > > uboot which float around.  For instance, on the OMAP4430 SDP, the
> > > following commands were used as supplied to load a uImage off the SD
> > > card into RAM at a different address to which it was built for, and
> > > execute it at that address:
> > > 
> > > mmcinit 0
> > > fatload mmc 0 0x80300000 uImage
> > > bootm 80300000
> > > 
> > > Whether the 'bootm' command then copied the image and called it there,
> > > or whether it executed it at 0x80300000 I've no idea - but why then
> > > load the image at a different address in the first place?
> > 
> > Yes, U-Boot's image handling looks at the image at 80300000, extracts the
> > "load address" from the image header, memcpy()'s the image to that address,
> > then jumps to the "entry address" in the image header.
> 
> Ah, so specifying that address is just a total waste of space then,
> because you might as well specify an address which results in the
> copy not being necessary.
> 
> However, I'd expect that uboot is dumb enough to still do the copy
> irrespective of whether its already in the right place.

U-Boot doesn't do an unnecessary copy if the body of the image is
already at the load address specified in the image header.

Unfortunately, it also doesn't do a copy if the header of the image is
at the load address, (I guess to support images constructed with an
embedded header). This means that

  fatload mmc 0 0x80300000 uImage
  bootm 0x80300000

will crash as it will attempt to boot Linux by executing the image
header. To successfully boot without requiring a relocation we would
need:

  fatload mmc 0 0x80300000-sizeof(header) uImage
  bootm 0x80300000

-- 
Tixy


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