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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
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Subject: Re: ARM Simulator Bug? 
In-reply-to: Your message of "Wed, 03 Sep 2003 10:13:53 BST."
             <3f55b0d1.2580.0@esatclear.ie> 
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Date: Wed, 03 Sep 2003 09:51:00 -0000
From: Richard Earnshaw <rearnsha@arm.com>
X-SW-Source: 2003-q3/txt/msg00139.txt.bz2

> Hi Richard,
> 
> >Try using an 
> >
> >	LDR r0, =__thumb
> >
> 
> This command places the correct value into R0 for the BX command, but the bug
> within the simulator is still present. 
> 
> Take the following code as an example.
> 
> 0000005c <TST_start>:
>   5c:   e3a0da12        mov     sp, #73728      ; 0x12000
>   60:   e59f00a4        ldr     r0, [pc, #164]  ; 10c <IRQ_Interrupt+0x50>
>   64:   e12fff10        bx      r0
> 
> 00000068 <__start_of_thumb>:
> 
> void    IRQ_Interrupt(void);
> 
> int main()
> {
>   68:   b580            push    {r7, lr}
>   6a:   466f            mov     r7, sp
>   6c:   b082            sub     sp, #8
> 
> If I place a breakpoint at 0x6c and run the code gdb loses itself, i.e. if I
> interrupt it with ctrl-c it says the PC is 0x0580fa70 or some thing similar.
> Again, if I place a breakpoint at 0x5c, I can single step successfully. If I
> single step to 0x68 and place a breakpoint at 0x6c and continue, gdb loses itself
> again.
> 
> This problem only occurs when I attempt to use thumb. If I remove the bx command
> and compile my C file in ARM mode the simulator works perfectly.

Hmm, you are building *all* of your source with -g aren't you?  gdb can 
get very confused if it doesn't know whether it's debugging ARM or Thumb 
code and it defaults to ARM when it doesn't know (another side-effect of 
no mapping symbols).

Another thing to consider:

Is the processor taking an abort on the push instruction and jumping into 
the abort handler?  Try putting an a breakpoint at address 0x00000010.  
Alternatively, check the value of SP before stepping the instruction.

> 
> Is it possible to see which commands the simulator is executing? 
> 

I'm not aware of any simple way to do that.  I agree that there are times 
when it would be useful.

R.