Re: Fix for PR 1971 .

[Ramana Radhakrishnan <ramana dot radhakrishnan at codito dot com>]

Hi Jim 

I am not sure about removing the get_prev_frame. We need it for the
correct frame id .  In case you were stepping over a recursive call and
deep inside after main had executed  you would need the correct frame id
of the return frame and in the other case a null_frame_id.  

Changing over breaks the behaviour of the backtrace over a recursive
call. Gives me  extra failures inside break.exp . 

cheers
Ramana

On Tue, 2006-01-03 at 21:55 -0800, Jim Blandy wrote:
> Hi --- thanks for revising the patch.
> 
> +/* Insert a step resume breakpoint at the return address of the
> +   caller. This is to ensure that on doing a next from before main completes
> +   execution of the program without GDB dumping core. Look at PR 1971
> +   for more details.  */
> 
> I don't think this is quite what you mean to say.  The comment for a
> function should describe its behavior in terms of its arguments;
> "caller" is vague.  Second, this isn't always used for "next"; it can
> get used when you "step" into a function with no debug info (if I'm
> reading right).  Third, a more self-contained explanation of why the
> get_prev_frame-based approach isn't sufficient would be better.
> 
> How about:
> 
> /* Insert a step-resume breakpoint at the address to which
>    RETURN_FRAME will return.
> 
>    Unlike insert_step_resume_breakpoint_at_frame (get_prev_frame (F)),
>    this works even when F is the oldest frame.  (Consider next-ing out
>    of main when 'show backtrace past-main' is off.)  */
> 
> Finally --- could insert_step_resume_breakpoint_at_caller simply
> *always* use the frame_pc_unwind approach, and drop the check for
> get_prev_frame altogether?  I understand that trying get_prev_frame
> first is guaranteed to give the least disturbance to the existing
> behavior, but I don't like leaving stuff like that in there unless we
> can explain why it's actually needed.
-- 
Ramana Radhakrishnan
GNU Tools
codito ergo sum (www.codito.com)
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