Re: Fix for PR 1971 .

[Jim Blandy <jimb@red-bean.com>]

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.