Debugging Python script that runs inside lldb

Question

I want to send commands to a neovim instance from a lldb (gdb) extension python script. While this works without a problem with gdb, i get a python exception in lldb.

Minimal example:

(gdb) source test.py #works
(lldb) command script import test.py #raises an exception

test.py

import pynvim
pynvim.attach('socket', path='/tmp/nvimsocket')

exception:

error: module importing failed: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object
  File "temp.py", line 1, in <module>                                          
  File "/opt/repos/nvim/test.py", line 5, in <module>    
    pynvim.attach('socket', path='/tmp/nvimsocket2') 
  File "/usr/lib/python3.8/site-packages/pynvim/__init__.py", line 122, in attach

    return Nvim.from_session(session).with_decode(decode)
  File "/usr/lib/python3.8/site-packages/pynvim/api/nvim.py", line 80, in from_session
    channel_id, metadata = session.request(b'nvim_get_api_info')
  File "/usr/lib/python3.8/site-packages/pynvim/msgpack_rpc/session.py", line 95, in request
    v = self._blocking_request(method, args)
  File "/usr/lib/python3.8/site-packages/pynvim/msgpack_rpc/session.py", line 174, in _blocking_request
    self._async_session.run(self._enqueue_request,
  File "/usr/lib/python3.8/site-packages/pynvim/msgpack_rpc/async_session.py", line 66, in run
    self._msgpack_stream.run(self._on_message)
  File "/usr/lib/python3.8/site-packages/pynvim/msgpack_rpc/msgpack_stream.py", line 43, in run
    self.loop.run(self._on_data)
  File "/usr/lib/python3.8/site-packages/pynvim/msgpack_rpc/event_loop/base.py", line 148, in run
    signal.signal(signal.SIGINT, default_int_handler)
  File "/usr/lib/python3.8/signal.py", line 47, in signal
    handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))

This seems to be an issue of the signal module an also affects other projects: https://github.com/python/asyncio/issues/396

It is possible to debug the python script that runs inside a virtual python env inside of lldb?

Edit:

If I try to import pdb and set a breakpoint with

pdb.set_trace()

(without the nvim stuff) this exception rises:

error: module importing failed: Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/test/python_debug/test.py", line 8, in <module>
    a()
  File "/home/test/python_debug/test.py", line 5, in a
    pdb.set_trace()
  File "/usr/lib/python3.8/pdb.py", line 1609, in set_trace
    pdb = Pdb()
  File "/usr/lib/python3.8/pdb.py", line 158, in __init__
    readline.set_completer_delims(' \t\n`@#$%^&*()=+[{]}\\|;:\'",<>?')
AttributeError: module 'lldb_editline' has no attribute 'set_completer_delims'

I built lldb from source, there are two flags:

LLDB_ENABLE_LIBEDIT
LLDB_ENABLE_CURSES

https://lldb.llvm.org/resources/build.html libedit is installed, how can I verify that it got activated? Is there something like lldb --build-flags ?

Answer 1

You can use Python's pdb module to insert tracepoints in your test.py and lldb will stop in the pdb shell and allow you to step through the code. E.g.:

 > lldb
(lldb) platform shell cat /tmp/test.py
print("About to break")
import pdb
pdb.set_trace()
print("Back from break.")
(lldb) command script impo /tmp/test.py
About to break
> /tmp/test.py(4)<module>()
-> print("Back from break.")
(Pdb) n
Back from break.
--Return--
> /tmp/test.py(4)<module>()->None
-> print("Back from break.")
(Pdb) c
(lldb)