GNU bug report logs - #70519
30.0.50; Device for Emacs terminal I/O

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: Helmut Eller <eller.helmut <at> gmail.com>, Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 70519 <at> debbugs.gnu.org
Subject: bug#70519: 30.0.50; Device for Emacs terminal I/O
Date: Tue, 23 Apr 2024 08:32:25 +0300

> From: Helmut Eller <eller.helmut <at> gmail.com>
> Date: Mon, 22 Apr 2024 22:09:18 +0200
> 
> I'd like to start Emacs under GDB, but so that Emacs doesn't use the
> same terminal as GDB.

You should be able to do that with GDB features.  These include:

  . the 'set inferior-tty' command
  . the 'set new-console' command

The first sets the terminal of the debuggee to the named terminal, the
latter causes GDB to create a new terminal each time you "run" a
debuggee, and force the debuggee to use that new terminal.  These
commands should work for you without any changes to the Emacs sources.

Alternatively, you could start GDB from a different terminal and
attach it to an already running Emacs, but this does not allow you to
debug the Emacs startup code.

> It seems that the --terminal command line switch is there for
> exactly this use case.
> 
> However, it doesn't work.  Emacs parses the command line option and
> replaces stdin and stdout with the correct device, but then in dispnew.c
> it always calls init_tty with 0 as argument for the device name.  That
> simply opens the controlling terminal, i.e. /dev/tty and that is usually
> the same device as the one that GDB uses.
> 
> What would you think of the change below?

I don't think it's the correct change.  For starters, ttyname is
non-portable: on some supported platforms there's no way of getting at
the name of a non-default terminal.

More importantly, we already know the name of the terminal: we used it
in emacs.c when we processed the --terminal switch.  We just "forgot"
it because we didn't save it anywhere.  So one way of fixing this is
to record that name and reuse it in init_tty.  E.g., make DEV_TTY
non-const, and save the actual name there when we process it in
emacs.c.

Adding Paul in case he has comments.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.