Query regarding assembly level debugging support

Tarun tarun@acmet.com
Wed Dec 8 07:04:00 GMT 2004



> -----Original Message-----
> From: Peter Barada [mailto:peter@the-baradas.com]
> Sent: Thursday, December 02, 2004 7:40 PM
> To: tarun@acmet.com
> Cc: gdb@sources.redhat.com; acmet@vsnl.net; ranjeeta@acmet.com;
> rm_nair@acmet.com
> Subject: Re: Query regarding assembly level debugging support
> 
> 
> >     The linked out file is loaded without errors on GDB. When we run
> >the respective out file on GDB, the control of debugger moves to
label
> >main in the assembly code ( Breakpoint 1, 0xa00200ec in main ()).
When I
> >try to move to next instruction using "nexti", the control moves to
next
> >address (Displaying: 0xa00200f0 in main ()). This continues till the
> >last address is reached. Only the address increments within the
assembly
> >file are displayed and not the actual assembly source.
> >
> >      When I try to single step using "step", the message prompted is
> >"Single stepping until exit from function main, which has no line
number
> >information". Whereas if I disassemble one of the addresses give
above,
> >entire assembly code which I am trying to debug is displayed.
> >
> >      Does this mean that GDB does not support debugging of the
assembly
> >code?
> 
> Peope have been using GDB to debug assembler code for years.  A
> couple of tricks:
> 
> 1) Use stepi/nexti commands to step or next one *instruction* as
>    opposed to source line
> 2) Use the 'disp/i $pc' to have GDB display the assembler instruction
>    that will be executed next.
> 3) Use 'i reg' to dump the registers, or 'p $reg' where 'reg' is the
>    register name.
> 
Thanks for the information. But my query still remains "Can we step
through assembly code?"
I know GDB supports assembly-level debugging but that refers to inline
assembly. To make the point clear, please look at snip below. For the
sample code segment:
<snip>
       /* Print the top of the stack if no index is specified. */
       if (which < 0)
         {
           which = stack->top - 1;
           if (which < 0)   
<snip>

The inline assembly is (assume) represented as: 
<snip>
       /* Print the top of the stack if no index is specified. */
       if (which < 0)
		.frame	$fp,16,$31	<-
		.mask	0x40000000,-8  <-
		.fmask	0x00000000,0   <-
		subu	$sp,$sp,16        <-
         {
           which = stack->top - 1;
		li	$2,20	            <-
		sw	$2,0($fp)           <-
           if (which < 0)   
<snip>


Does GDB refer to stepping through the above code as assembly-level
debugging?

If yes, then my requirement is little different. I want to debug the
assembly code itself keeping it as the source code (and not the C
source). To be more specific I want to debug hand written assembly code
(and not the one generated by compiler)


Regards,
Tarun



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