linux-kernel - Re: [PATCH] i386: always clear bss

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Message-ID: <463B6888.20001@zytor.com>
Date:	Fri, 04 May 2007 10:08:24 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i386: always clear bss

Eric W. Biederman wrote:
>>>
>> I saw the 0x40(%esi) stack stuff, and I'm utterly puzzled by it.  There
>> is no reason one can't set up %esp to point to a hunk in ordinary memory
>> and use it?
> 
> That is what we are doing, remind me to make certain we have this
> field of the boot protocol documented as permanently reserved for
> this.
> 
> This comes from the relocatable kernel patches where we run the
> kernel where the bootloader chooses to put it assuming we are >= 1M.
> 
> The problem is that we don't have any IP relative data access
> instructions, we don't have a stack, and so the only valid address
> that we know is valid is %esi.  Once we compute where we are running
> we can setup a base address register and a stack and everything is
> easy, but the bootstrap to figure out where we are is just a little
> tricky.

Oh, right.  And this runs with interrupts off, so you only need one
dword.  That's fine, of course, although the location is a bit awkward.

	-hpa
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