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

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Message-ID: <m17iroqzlq.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 04 May 2007 11:15:45 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.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

"H. Peter Anvin" <hpa@...or.com> writes:

> 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.

Yep.  That is what I found when surveyed the available locations.

Eric
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