linux-kernel - Re: [PATCH] [2/9] Add a kernel_address() that works for data too

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Message-ID: <20100105190455.GE30868@flint.arm.linux.org.uk>
Date:	Tue, 5 Jan 2010 19:04:55 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-arch@...r.kernel.org,
	ebiederm@...ssion.com, paulmck@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [2/9] Add a kernel_address() that works for data too

On Tue, Jan 05, 2010 at 09:58:53AM +0100, Sam Ravnborg wrote:
> But you can trust _etext an almost all architectures.
> It is a bug if it is missing.
> 
> So [_text, _etext] is the text section.
> 
> The data section may be placed before or after - it depends on the architecture.
> But again - only some architectures define _sdata.
> But all? define _edata.

You can not guarantee that the data segment is after the text segment,
unless you want to outlaw XIP kernels.  XIP kernels have the text
segment mapped at a completely different address to the data segment.

I'd suggest the only way to identify the data segment in a generic way
is to have everyone define _sdata, or more preferably _data (to be
consistent with _text), to be the start of the data segment.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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