Re: GDB/MI and ">" prompts

Eli Zaretskii
2012-04-19T19:25:27Z

> Date: Thu, 19 Apr 2012 11:53:29 -0700
> From: Joel Brobecker <brobecker@adacore.com>
> Cc: gdb@sourceware.org
>
> > With this knowhow in hand, my next question is about GDB/MI behavior
> > when it is connected to a tty device. Typing
> >
> > -interpreter-exec console "commands"
> >
> > from the console for some reason disables the ">" prompts for the
> > breakpoint commands. If stdin is NOT a tty, those prompts _are_
> > output. Why the difference?
>
> I don't know if it is a feature or a bug. I would lean towards a bug.
> GDB treats all prompts the same, and asks the current interpreter
> whether to display the prompt or not. See gdb_readline_wrapper,

Do we really use readline when MI is the interpreter?

> which calls display_gdb_prompt, which does:
>
> /* Each interpreter has its own rules on displaying the command
> prompt. */
> if (!current_interp_display_prompt_p ())
> return;
>
> Although we are executing the command using the console interpreter,
> the current interpreter remains the GDB/MI interpreter:
>
> (top-gdb) p *current_interpreter
> $11 = {name = 0x19b8ce0 "mi", next = 0x19b9ec0, data = 0x1a32390,
> inited = 1, procs = 0x94d480, quiet_p = 0}
>
> And thus, current_interp_display_prompt_p returns false.
>
> Just to see what would happen if the GDB/MI interpreter was to
> display prompts, I tweaked mi_interpreter_prompt_p to always
> return 1, and here is what I get:
>
> -interpreter-exec console "commands 1"
> ~"Type commands for breakpoint(s) 1, one per line.\nEnd with a line saying just \"end\".\n"
> ~">"
> print 1
> ~">"
> print 2
> ~">"
> end
>
> The ~ lines are lines that would be printed verbatim on the debugger
> console, so I believe the user experience would be similar to what
> we get in non-MI mode.

Right. But you don't need to hack the code to see this in action,
just "set interactive-mode off" and you will see it.

The crux of my question was why non-interactive mode does display a
prompt while the interactive one doesn't.

> But of course, things are not as simple as this, since I do not think
> we want the GDB/MI to always print the prompt.

Does GDB/MI have a prompt? The ">" thing is coming from the CLI, not
from MI. Or did you mean other prompts in other situations (and if
so, which ones)?

> The other thing that occured to me was that, perhaps, we should instead
> be switching the interpreter while executing the console command,

How would that help?