linux-kernel - Re: [i386] Questions regarding provisional page tables initialization

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Message-ID: <20070702154313.GA2619@Ahmed>
Date:	Mon, 2 Jul 2007 18:43:13 +0300
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Brian Gerst <bgerst@...ntduck.org>
Cc:	Andreas Schwab <schwab@...e.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [i386] Questions regarding provisional page tables initialization

On Mon, Jul 02, 2007 at 07:34:20AM -0400, Brian Gerst wrote:
> Ahmed S. Darwish wrote:
> > now back to head.S code:
> >  	leal    0x007(%edi),%ecx	/* Create PDE entry */
> > 
> > Isn't the above line the same condition (bytes, not bits displacement) ?. 
> > Thanks for your patience !.
> 
> The leal instruction (Load Effective Address) is often used as a way to
> add a constant to one register and store the result in another register
> in a single instruction.
> [...]

At last I got it due to all of everybody's very nice explanations :). 
Here's the provisional page tables intialization scenario:

We want to store pg0 pte addresses to high 20bits swapper_pg_dir entries,
we also want the PRESENT,RW,USER flags be set in those entries. This is 
done by  getting the address of each pg0 entry and adding 7 to it (Brian's
note). Since pg0 entires address are page aligned(Andreas, Jeremy notes),
adding 7 will assure that the first 3 bits are set without affecting the
high 20 bits.

Big Thanks!,

-- 
Ahmed S. Darwish
HomePage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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