From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gdb-return-28230-listarch-gdb=sources.redhat.com@sourceware.org>
Received: (qmail 20397 invoked by alias); 26 Mar 2007 05:55:45 -0000
Received: (qmail 20389 invoked by uid 22791); 26 Mar 2007 05:55:44 -0000
X-Spam-Check-By: sourceware.org
Received: from smtp1.dnsmadeeasy.com (HELO smtp1.dnsmadeeasy.com) (205.234.170.134)     by sourceware.org (qpsmtpd/0.31) with ESMTP; Mon, 26 Mar 2007 06:55:41 +0100
Received: from smtp1.dnsmadeeasy.com (localhost [127.0.0.1]) 	by smtp1.dnsmadeeasy.com (Postfix) with ESMTP id A187C29A7A3; 	Mon, 26 Mar 2007 05:55:39 +0000 (GMT)
X-Authenticated-Name: js.dnsmadeeasy
X-Transit-System: In case of SPAM please contact abuse@dnsmadeeasy.com
Received: from avtrex.com (unknown [67.116.42.147]) 	by smtp1.dnsmadeeasy.com (Postfix) with ESMTP; 	Mon, 26 Mar 2007 05:55:39 +0000 (GMT)
Received: from [192.168.7.223] ([192.168.7.223]) by avtrex.com with Microsoft SMTPSVC(6.0.3790.1830); 	 Sun, 25 Mar 2007 22:55:37 -0700
Message-ID: <46076056.10301@avtrex.com>
Date: Mon, 26 Mar 2007 05:55:00 -0000
From: David Daney <ddaney@avtrex.com>
User-Agent: Thunderbird 1.5.0.10 (X11/20070302)
MIME-Version: 1.0
To: "Develop.ReactOS" <develop.reactos@gmail.com>
Cc: gdb <gdb@sourceware.org>
Subject: Re: Need help debuging i386 in real mode.
References: <200703251435091123125@gmail.com>
In-Reply-To: <200703251435091123125@gmail.com>
Content-Type: text/plain; charset=GB2312
Content-Transfer-Encoding: 7bit
X-IsSubscribed: yes
Mailing-List: contact gdb-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <gdb.sourceware.org>
List-Subscribe: <mailto:gdb-subscribe@sourceware.org>
List-Archive: <http://sourceware.org/ml/gdb/>
List-Post: <mailto:gdb@sourceware.org>
List-Help: <mailto:gdb-help@sourceware.org>, <http://sourceware.org/ml/#faqs>
Sender: gdb-owner@sourceware.org
X-SW-Source: 2007-03/txt/msg00308.txt.bz2

Develop.ReactOS wrote:
> Hello:
>     I am trying to debug i386 in real mode. How to disassemble 16-bit code?
>     gdb appears to always assume a 32-bit segment.Is there a way to coerce gdb into 16-bit disassembly mode?  Is there some other tool or cmd I could use?  
>
> I need 16-bit disassembly instruction,but gdb's output is wrong:
> (gdb) x /10i $eip+$cs*16
> 0xffff0:        ljmp   0x3131,0xf000e05b
> 0xffff7:        das
> 0xffff8:        xor    BYTE PTR [ecx],dh
> 0xffffa:        das
> 0xffffb:        xor    BYTE PTR [esi],dh
> 0xffffd:        add    ah,bh
> 0xfffff:        test   DWORD PTR [eax],0x0
> 0x100005:       add    BYTE PTR [eax],al
> 0x100007:       add    BYTE PTR [eax],al
> 0x100009:       add    BYTE PTR [eax],al
>
>   
I have not tested it, but it looks like the GNU binutils objdump program
can do it. If you can get an image of the memory area you want to
disassemble into a file try something like:

objdump --target=binary --architecture=i8086 --disassemble-all
memory_image_filename

David Daney