linux-kernel - Re: [PATCH v3 02/31] arm64: Kernel booting and initialisation

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Message-ID: <20120910145329.GE27042@arm.com>
Date:	Mon, 10 Sep 2012 15:53:29 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 02/31] arm64: Kernel booting and initialisation

On Mon, Sep 10, 2012 at 03:48:20PM +0100, Arnd Bergmann wrote:
> On Monday 10 September 2012, Nicolas Pitre wrote:
> > On Mon, 10 Sep 2012, Arnd Bergmann wrote:
> > > On Monday 10 September 2012, Catalin Marinas wrote:
> > > > On Mon, Sep 10, 2012 at 06:53:39AM +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > > I think a bunch of other architectures can have relocatable kernels, which
> > > is useful e.g. for kdump. It does imply a small runtime cost and may have
> > > other disadvantages though.
> > 
> > Relocatable in physical space is what kdump actually needs, and that's 
> > what we already have here (as well as on ARM32 for that matter with 
> > CONFIG_ARM_PATCH_PHYS_VIRT).  Relocatable in the virtual space is costly 
> > and we shouldn't need to go there.
> 
> Ah, I see. I thought that the other architectures (powerpc and x86)
> doing this were actually building with -fPIC, but they do the same
> kind of early patching that we do.

On arm64 I don't have run-time code patching (yet) but a PHYS_OFFSET
variable set at boot time. It may prove useful to have run-time code
patching but that's just an optimisation that can be added later.

-- 
Catalin
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