Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Michal Simek <monstr@monstr.eu>,
	Nicolas Pitre <nicolas.pitre@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Joel Fernandes <joelf@ti.com>,
	linux-arm-msm@vger.kernel.org,
	Stephen Boyd <sboyd@codeaurora.org>,
	Peter Crosthwaite <peter.crosthwaite@xilinx.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Christopher Covington <cov@codeaurora.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig
Date: Tue, 22 Apr 2014 11:53:25 -0600	[thread overview]
Message-ID: <20140422175325.GD23955@obsidianresearch.com> (raw)
In-Reply-To: <20140422171141.GW24070@n2100.arm.linux.org.uk>

On Tue, Apr 22, 2014 at 06:11:42PM +0100, Russell King - ARM Linux wrote:

> Put another way, if your platform is part of the multi-platform kernel
> then you are *excluded* from being able to use this... unless you hack
> the Kconfig, and then also provide a constant value for PHYS_OFFSET,
> thereby _tying_ the kernel you built to a _single_ platform.

That is exactly right. To get a fixed LMA you must commit to a
non-relocatable kernel image.

Realistically this patch would need to be accompanied by something
that makes ARM_PATCH_PHYS_VIRT optional for multiplatform based on
EXPERT or similar.

The best usecase seems to be to support ELF tooling for low level
debugging activities, a non-relocatable image isn't a blocker for that
case.

Since the patch is a no-op if LOAD_OFFSET isn't set, is there a
downside I don't see?

Thanks,
Jason