From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gdb-return-15355-listarch-gdb=sources.redhat.com@sources.redhat.com>
Received: (qmail 798 invoked by alias); 2 Sep 2003 18:17:23 -0000
Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm
Precedence: bulk
List-Subscribe: <mailto:gdb-subscribe@sources.redhat.com>
List-Archive: <http://sources.redhat.com/ml/gdb/>
List-Post: <mailto:gdb@sources.redhat.com>
List-Help: <mailto:gdb-help@sources.redhat.com>, <http://sources.redhat.com/ml/#faqs>
Sender: gdb-owner@sources.redhat.com
Received: (qmail 734 invoked from network); 2 Sep 2003 18:17:17 -0000
Received: from unknown (HELO cam-admin0.cambridge.arm.com) (193.131.176.54)
  by sources.redhat.com with SMTP; 2 Sep 2003 18:17:17 -0000
Received: from pc960.cambridge.arm.com (pc960.cambridge.arm.com [10.1.205.4])
	by cam-admin0.cambridge.arm.com (8.9.3/8.9.3) with ESMTP id TAA05399;
	Tue, 2 Sep 2003 19:17:00 +0100 (BST)
Received: from pc960.cambridge.arm.com (rearnsha@localhost)
	by pc960.cambridge.arm.com (8.11.6/8.9.3) with ESMTP id h82IH0b21887;
	Tue, 2 Sep 2003 19:17:00 +0100
Message-Id: <200309021817.h82IH0b21887@pc960.cambridge.arm.com>
X-Authentication-Warning: pc960.cambridge.arm.com: rearnsha owned process doing -bs
To: mckennad@esatclear.ie
cc: Richard Earnshaw <rearnsha@arm.com>, gdb@sources.redhat.com,
        insight@sources.redhat.com, Richard.Earnshaw@arm.com
Reply-To: Richard.Earnshaw@arm.com
Organization: ARM Ltd.
X-Telephone: +44 1223 400569 (direct+voicemail), +44 1223 400400 (switchbd)
X-Fax: +44 1223 400410
X-Address: ARM Ltd., 110 Fulbourn Road, Cherry Hinton, Cambridge CB1 9NJ.
X-Url: http://www.arm.com/
Subject: Re: ARM Simulator Bug? 
In-reply-to: Your message of "Tue, 02 Sep 2003 15:31:11 BST."
             <3f54a9af.472.0@esatclear.ie> 
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Date: Tue, 02 Sep 2003 18:17:00 -0000
From: Richard Earnshaw <rearnsha@arm.com>
X-SW-Source: 2003-09/txt/msg00018.txt.bz2

> Hi Richard,
> 
> Thanks for the reply.
> 
> >It's more likely to be the way you are trying to get into Thumb state.  Try
> 
> >
> >	adr	r0, __start_of_thumb
> 
> Should this line not be
> 
> 	adr	r0, __start_of_thumb+1
> 
> To set the LSB to tell the core we want to enter Thumb mode
> 

Well, no.  If the bottom bit isn't being set automatically when the target 
is a thumb symbol then that's really a bug in the tools.


> >	bx	r0
> >	.code 16
> >	.global __start_of_thumb
> >	.thumb_func
> >__start_of_thumb:
> >
> >
> >This is really brokenness in the way gas implements ARM and Thumb code 
> >areas, but it's hard to fix properly until GAS starts using mapping 
> >symbols.
> 
> If I use the +1 code above, and set a breakpoint at the adr command, I can single
> step successfully past the BX command and into my main.

It appears that GAS is broken:

$ cat test.s
	.arm
	adr	r0, __thumb
	bx	r0
	.thumb
	.globl	__thumb
	.thumb_func
__thumb:
	nop

$ arm-elf-as test.s -o test.o
$ arm-elf-objdump -dr test.o

test.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <__thumb-0x8>:
   0:   e28f0000        add     r0, pc, #0      ; 0x0	####### Bzzt no!
   4:   e12fff10        bx      r0

00000008 <__thumb>:
   8:   46c0            nop                     (mov r8, r8)

Try using an 

	LDR r0, =__thumb

expression.  You'll need to squeeze the constant pool in somewhere.

R.