From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760607AbXFVXBW (ORCPT ); Fri, 22 Jun 2007 19:01:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751422AbXFVXAx (ORCPT ); Fri, 22 Jun 2007 19:00:53 -0400 Received: from moutng.kundenserver.de ([212.227.126.174]:60535 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751279AbXFVXAw (ORCPT ); Fri, 22 Jun 2007 19:00:52 -0400 From: Bodo Eggert <7eggert@gmx.de> Subject: Re: how to tell linux (on x86) to ignore 1M or memory To: Rene Herman , "H. Peter Anvin" , Bart Trojanowski , linux-kernel@vger.kernel.org Reply-To: 7eggert@gmx.de Date: Sat, 23 Jun 2007 01:00:17 +0200 References: <8bFEz-3B4-39@gated-at.bofh.it> <8c6EE-4Jj-5@gated-at.bofh.it> <8yGrK-4vX-7@gated-at.bofh.it> <8yRnb-4XE-23@gated-at.bofh.it> User-Agent: KNode/0.7.2 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8Bit Message-Id: X-be10.7eggert.dyndns.org-MailScanner-Information: See www.mailscanner.info for information X-be10.7eggert.dyndns.org-MailScanner: Found to be clean X-be10.7eggert.dyndns.org-MailScanner-From: 7eggert@gmx.de X-Provags-ID: V01U2FsdGVkX1/4haRKT1IJQRhgmgcywggANzFl+oimeFnEc3W Yh43rNBJBZKlGkEFtj20bAVQQizoYzmxcyuWvzSANJHPUtGG6S yqpLApVlK8rTtfF5cuI2A== Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Rene Herman wrote: > The point was that real mode could only access the first 1M, not > the first 16... :-) The real mode on i386+ can actually access the whole 4GB address range due to a former-bug-now-feature in the i386+. This "bug" causes the segment limit to not be reset on return to real mode, but only on subsequent assigns to the segment registers/selectors. Using a rarely used segment register like GS, you could use extended memory in your program. Obviously this needs 1) Entering and returning from protected mode, 2) all programs to agree not to clobber GS and 3) not using v86 mode (EMM386.exe). Therefore and because it was discovered in the late days of DOS it was not in widespread use. Some DOS extenders were reported to use it ... http://www.programmersheaven.com/mb/x86_asm/344953/344953/readmessage.aspx -- The programmer's National Anthem is 'AAAAAAAAHHHHHHHH' Friß, Spammer: vO9EZegbA@hBtpA.7eggert.dyndns.org maFsnwE@Fvznj.7eggert.dyndns.org mhF-@PoxRjk.7eggert.dyndns.org