From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gdb-patches-return-18292-listarch-gdb-patches=sourceware.cygnus.com@sources.redhat.com>
Received: (qmail 26504 invoked by alias); 30 Aug 2002 19:10:52 -0000
Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm
Precedence: bulk
List-Subscribe: <mailto:gdb-patches-subscribe@sources.redhat.com>
List-Archive: <http://sources.redhat.com/ml/gdb-patches/>
List-Post: <mailto:gdb-patches@sources.redhat.com>
List-Help: <mailto:gdb-patches-help@sources.redhat.com>, <http://sources.redhat.com/ml/#faqs>
Sender: gdb-patches-owner@sources.redhat.com
Received: (qmail 26497 invoked from network); 30 Aug 2002 19:10:51 -0000
Received: from unknown (HELO freya.inter.net.il) (192.114.186.14)
  by sources.redhat.com with SMTP; 30 Aug 2002 19:10:51 -0000
Received: from Zaretsky ([80.230.2.40])
	by freya.inter.net.il (Mirapoint Messaging Server MOS 3.1.0.58-GA)
	with ESMTP id BSH47668;
	Fri, 30 Aug 2002 22:09:51 +0300 (IDT)
Date: Fri, 30 Aug 2002 12:31:00 -0000
From: "Eli Zaretskii" <eliz@is.elta.co.il>
To: drow@mvista.com
Message-Id: <2950-Fri30Aug2002221152+0300-eliz@is.elta.co.il>
CC: ac131313@ges.redhat.com, gdb-patches@sources.redhat.com
In-reply-to: <20020829213653.GA24048@nevyn.them.org> (message from Daniel
	Jacobowitz on Thu, 29 Aug 2002 17:36:53 -0400)
Subject: Re: [rfc] 16 bit real-mode for the i386
Reply-to: Eli Zaretskii <eliz@is.elta.co.il>
References: <3D6E8453.5080306@ges.redhat.com> <20020829213653.GA24048@nevyn.them.org>
X-SW-Source: 2002-08/txt/msg01042.txt.bz2

> Date: Thu, 29 Aug 2002 17:36:53 -0400
> From: Daniel Jacobowitz <drow@mvista.com>
> 
> > +static void
> > +i386_write_pc (CORE_ADDR pc, ptid_t ptid)
> > +{
> > +  if (i386_real_mode_p)
> > +    {
> > +      CORE_ADDR cs = read_register_pid (CS_REGNUM, ptid);
> > +      pc = pc - (cs << 4);
> > +    }
> > +  write_register_pid (PC_REGNUM, pc, ptid);
> > +}
> > +
> 
> Left shift of _four_?  Surely the PC is more than four bits.

It's true that PC can be more than 4 bits, but the code above is still
correct.  That's why real mode can only access 20 bit addresses:
16+4=20.

You can look at this issue this way: for each linear 2-bit address,
there are many CS:PC combination that all point to that address.