Problem setting registers if stack point or frame pointer is 0

[Daniel Jacobowitz]

On Thu, Apr 03, 2008 at 10:35:41PM +0100, Antony KING wrote:
> Hi,
>
> I have a problem trying to set a CPU register (using the GDB convenience  
> variable mechanism) if the stack pointer (SP) or frame pointer (FP) CPU  
> registers are 0. For example on an SH-4 device, where the FP register is  
> R14 and the SP register is R15, I see the following error from GDB 
> (6.7.1):

This is an unfortunate design problem in GDB.  You've found the right
comment, but in fact the comment lies.

  /* ZERO denotes the null frame, let the caller decide what to do
     about it.  Should it instead return get_current_frame()?  */

It doesn't denote just the null frame (nothing running).  It also
denotes the last frame (can not unwind past here, outermost).  We've
really got to get rid of that ambiguity.

I use a terrible hack in find_frame_by_id in our tools, since I
still haven't found time to return to this problem :-(

-- 
Daniel Jacobowitz
CodeSourcery