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

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Message-ID: <p731wfr3x30.fsf@bingen.suse.de>
Date:	02 Jul 2007 12:43:15 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [i386] Questions regarding provisional page tables initialization

"Ahmed S. Darwish" <darwish.07@...il.com> writes:
> 
> There're some stuff that confused me for a full day about the code (head.S)
> that  accomplishes the above words:
> 
> 	movl $(pg0 - __PAGE_OFFSET), %edi
> 	movl $(swapper_pg_dir - __PAGE_OFFSET), %edx	
> 	movl $0x007, %eax			/* 0x007 = PRESENT+RW+USER */
> 10:
> 	leal $0x007(%edi),%ecx			/* Create PDE entry */
> 
> What does the address of 7 bytes displacement after %edi - the physical address
> of pg0 - represent ?. 

The trick is not to know everything, but to know where to look ...

Page table entries use the first 12 bits for various flags. Take a look
at the Intel or AMD x86 documentation from their websites.

-Andi
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