[RFA/RFC] New command: ``start''

[Joel Brobecker]

> > We could get rid of the caching mechanism, and recompute name_of_main
> > everytime (unless found in the debug info), but I think that would be
> > very costly, especially with graphical front-ends that have a tendency
> > of asking for the callstack at every stop...
> 
> I don't think it would be costly.  However, I think it would be very
> confusing!  Consider: we're in an Ada routine.  We backtrace.  This is
> the main program, so the backtrace stops at this procedure.  We
> single-step into a C subroutine and backtrace; now the backtrace goes
> back to the Ada procedure and then back again further!

Yes, very confusing indeed.

> I'm having the same problem reviewing this that I did with
> SYMBOL_SEARCH_NAME: namely, you're introducing interfaces that don't
> exist in our Ada support files, without the Ada implementation of the
> interface.  Could you show me what the Ada function for guessing the
> name of main does?

That's because the command name we've been using for that was "begin".
But people prefered "start" (which I like better too), so I changed
the name.

Here is how we find the name of the main procedure: We lookup a certain
symbol which is created by our binder, __gnat_ada_main_program_name.
This symbol points to a string holding the name of the main procedure.
You'll find the code in ada-lang.c:begin_command().

BTW: I think Paul was working on submitting a more recent version of
the ada-* files. I'll double-check with him.

> I think the best approach may be to iterate over the languages
> included in the object file, asking each of them whether this language
> appears to contain a main procedure.  Or even to simply skip the
> langhook complexity and just call an Ada find-main function!  For gcj
> I suspect we will just change the debug information.

I thought about several approaches along the same idea. One of them
was to implement a sniffing mechanism, with certain sniffers having
certain priorities. But you know, I really like the idea of dropping
the langhook, and just call the ada function. Something like this:

        char *
        main_name ()
        {
          /* If we found the name of main from the debug info, or
             already looked it up, then return the name of main.  */
          if (name_of_main != NULL)
            return name_of_main;

          /* Is the main in Ada?  */
          tmp_main_name = ada_find_main_name ();
          if (tmp_main_name != NULL)
            {
              set_main_name (tmp_main_name);
              return name_of_main;
            }

          /* Is the main in Java?  */
          tmp_main_name = java_find_main_name ();
          [etc...]

          /* Fallback: main_name must be the usual "main".  */
          set_main_name ("main);
          return name_of_main;
        }

The only drawback I see from this is that I will need to include
ada-lang.h. It would have been nice to avoid this, which is possible
with the langhooks. I could also add the ada_find_main_name()
declaration in another more common .h file, but that would be a dirty
trick, IMO.

-- 
Joel