From owner-freebsd-hackers@FreeBSD.ORG  Thu Aug 21 17:50:26 2008
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id A160D106564A
	for <freebsd-hackers@freebsd.org>; Thu, 21 Aug 2008 17:50:26 +0000 (UTC)
	(envelope-from jgordeev@dir.bg)
Received: from dir.bg (mail.dir.bg [194.145.63.28])
	by mx1.freebsd.org (Postfix) with ESMTP id 280EF8FC33
	for <freebsd-hackers@freebsd.org>; Thu, 21 Aug 2008 17:50:25 +0000 (UTC)
	(envelope-from jgordeev@dir.bg)
Received: from [77.85.117.184] (account jgordeev@dir.bg HELO
	sometimes2.studgrad.net) by srv.dir.bg (CommuniGate Pro SMTP 5.2.4)
	with ESMTPSA id 36182615 for freebsd-hackers@FreeBSD.ORG;
	Thu, 21 Aug 2008 20:20:20 +0300
Message-ID: <48ADA3D1.30802@dir.bg>
Date: Thu, 21 Aug 2008 20:20:17 +0300
From: Jordan Gordeev <jgordeev@dir.bg>
User-Agent: Mozilla/5.0 (X11; U; DragonFly i386; en-US;
	rv:1.8.1.16) Gecko/20080804 SeaMonkey/1.1.11
MIME-Version: 1.0
To: freebsd-hackers@FreeBSD.ORG
References: <200808211637.m7LGbRhJ008358@lurza.secnetix.de>
In-Reply-To: <200808211637.m7LGbRhJ008358@lurza.secnetix.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: 
Subject: Re: Boot loader + malloc
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 21 Aug 2008 17:50:26 -0000

Oliver Fromme wrote:
> Hello,
>
> I've got a small question regarding $subject.  I'm looking
> at this code snippet from src/sys/boot/i386/loader/main.c:
>
> #if defined(LOADER_BZIP2_SUPPORT) || defined(LOADER_FIREWIRE_SUPPORT)
>     heap_top = PTOV(memtop_copyin);
>     memtop_copyin -= 0x300000;
>     heap_bottom = PTOV(memtop_copyin);
> #else
>     heap_top = (void *)bios_basemem;
>     heap_bottom = (void *)end;
> #endif
>     setheap(heap_bottom, heap_top);
>
> If I understand correctly, the boot loader will use only
> low memory (i.e. below 0x100000) for malloc by default.
> Extended memory is only used if bzip2 or firewire support
> are enabled (not default).  Is this intentional?  Would it
> make sense to toggle the default and always use extended
> memory, unless disabled?
>
> I'm asking because the upcoming graphics support requires
> a little bit of memory for fonts and images, but there's
> only less than about 80 KB left in low memory, which is
> insufficient except for very trivial things.  The loader
> kept crashing on me in nasty ways because of that.
>
> In my p4 branch I modified the above #if to also use
> extended memory if LOADER_GRAPHICS_SUPPORT is defined,
> giving me 3 MB of memory to play with, which is plenty.
> Is that OK, or should I expect trouble?
>
> Any comments are appreciated.
>
> Best regards
>    Oliver
>
>   

At present the amd64 kernel is loaded just above the first megabyte of 
physical memory.
I have no idea if the loader uses malloc()/free() after the kernel is 
loaded though.