FWIW I recently debugged the Ableton link external on macOS using lldb. As mentioned previously, I build both Pd *and* the external with debugging symbols using "-g". One thing to check: may sure you are loading the external you built and not pre-existing binary somewhere in your path.

On Apr 12, 2018, at 12:00 PM, pd-list-request@lists.iem.at wrote:

Date: Thu, 12 Apr 2018 11:18:22 +0200
From: David Medine <dmedine@ucsd.edu>
To: pd-list@lists.iem.at
Subject: Re: [PD] debugging complex extern
Message-ID: <ea2afee2-a644-78f3-8c7b-5f13ec66e4da@ucsd.edu>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

@Miller, no I hadn't. Thanks! I knew there was something like that I had 
neglected. Now I am able to debug with gdb.

@iohannes, I am still having trouble with this technique. If I run Pd 
from the gdb prompt (with -nrt and -stderr) and a break point within the 
extern (meaning object not compiled into pd) nothing happens when I run 
the function where I want to break. If I follow the instructions on 
Hans' tutorial (run pd in a separate process then attach gdb to it) Pd 
simply hangs when I hit the break point and gdb doesn't appear to do 
anything.

--------
Dan Wilcox
@danomatika
danomatika.com
robotcowboy.com