python-gdb-ctrl 1.0.1

A thin layer on top of GDB to control it programatically.

python-gdb-ctrl is a thin interface on top of GDB, the debugger of the GNU Project.

It will let you to spawn and control the debugger from a Python console or program.

python-gdb-ctrl has two use modes: asynchronous and synchronous.

The former is intended to be used by another application, the latter is more a toy-example but handy while experimenting from a Python console.

GDBCtrl - Asynchronous interface

The class GDBCtrl is suitable from integrating python-gdb-ctrl and the debugger with an UI or other event-based software.

It has the basic primitives: - spawn: to run the debugger - shutdown: to quit or kill the debugger - send: to send GDB commands - recv: to receive GDB records

All of them are coroutines that can be integrated in an asyncio loop.

Note: due limitations in one of the dependencies of python-gdb-ctrl all the primitives except recv may block as they are not full asynchronous.

SyncGDBCtrl - Synchronous interface

While GDBCtrl is the class that you should use in a program, it is much easier to play interactively with SyncGDBCtrl.

>>> from gdb_ctrl import SyncGDBCtrl
>>> gdb = SyncGDBCtrl(force_styling=None)

The spawn and shutdown methods now are normal methods (they are not coroutines)

>>> gdb.spawn()

The same applies for send and recv

>>> gdb.send('file example/glad')
'<token>'

However a synchronous recv is tricky because GDB may return several records for a given send so you need to know beforehand how many times you need to call recv:

>>> gdb.recv()
{'type': 'Log', 'value': 'file example/glad\n'}

>>> gdb.recv()
{'type': 'Console', 'value': 'Reading symbols from example/glad...'}

>>> gdb.recv()
{'type': 'Console', 'value': 'done.\n'}

>>> gdb.recv()      # byexample: +paste
{'class': 'done', 'token': <token>, 'type': 'Result'}

>>> gdb.recv()
'(gdb)'

Notice how the send returned a <token>: you can use this to pair the command with its result.

Unfortunately this works only for the results, other GDB responses will not have this token so you cannot know if the Log response above is the product of the execution of file example/glad or it is the product of other command.

Using the synchronous recv is annoying: you need to know how many responses you will receive.

SyncGDBCtrl is mostly for interactive session so it provides handy execute method to send a command and receive the records in one shot taking care of retrieving all the responses.

This is specially useful for certain commands that they do more than one thing.

The start command is an example of this:

>>> gdb.execute('start')
Temporary breakpoint 1 <...>: file glad.c, line 52.
Notify:
{'bkpt': {'addr': '<...>',
          'disp': 'del',
          'enabled': 'y',
          'file': 'glad.c',
          'fullname': '<...>/example/glad.c',
          'func': 'main',
          'line': '52',
          <...>
          'times': '0',
          'type': 'breakpoint'}}
Starting program: /home/user/proj/python-gdb-ctrl/example/glad
<...>
Running
Exec: {'thread-id': 'all'}
<...>
Notify:
{'bkpts': [{'addr': '<...>',
            'disp': 'del',
            'enabled': 'y',
            'file': 'glad.c',
            'fullname': '<...>/example/glad.c',
            'func': 'main',
            'line': '52',
            'number': '1',
            'original-location': 'main',
            'thread-groups': ['i1'],
            'times': '1',
            'type': 'breakpoint'}]}
<...>
Temporary breakpoint 1, main (argc=1, argv=0x<...>) at glad.c:52
52          pthread_create(&th, NULL, release_neurotoxins, NULL);
Exec:
{'bkptno': '1',
 <...>
 'reason': 'breakpoint-hit',
 'stopped-threads': 'all',
 'thread-id': '1'}
<...>

That’s a lot! When GDB executes start, it sets a temporal breakpoint in the main function, it runs the binary and it notifies us when the breakpoint is hit and the program is stopped.

That generates a lot of messages (in fact I omitted several ones).

For convenience, execute() will print what it receives so you don’t need to parse anything.

If you want to use SyncGDBCtrl programmatically you can but I would recommend against it and use GDBCtrl instead.

A pythonic interface

Besides execute(), SyncGDBCtrl can be extended with several methods that will call a GDB command in a pythonic way:

>>> gdb.extend_interface_with_gdb_commands()

Now instead of calling execute('list') you can call list directly.

>>> gdb.list()
47          return 0;
48      }
49
50      int main(int argc, char *argv[]) {
51          pthread_t th;
52          pthread_create(&th, NULL, release_neurotoxins, NULL);
53
54          int cores[CORES] = {1};
55
56          for (int i = 1; i < argc; ++i) {
Done

The beauty of this is that you can request the documentation from a Python shell:

>>> print(gdb.list.__doc__)
<...>
List specified function or line.
With no argument, lists ten more lines after or around previous listing.
"list -" lists the ten lines before a previous ten-line listing.
One argument specifies a line, and ten lines are listed around that line.
Two arguments with comma between specify starting and ending lines to list.
Lines can be specified in these ways:
  LINENUM, to list around that line in current file,
  FILE:LINENUM, to list around that line in that file,
  FUNCTION, to list around beginning of that function,
  FILE:FUNCTION, to distinguish among like-named static functions.
  *ADDRESS, to list around the line containing that address.
With two args, if one is empty, it stands for ten lines away from
the other arg.
<...>

Note: GDB commands that have an invalid name for Python will be
prefixed with a ``z``

Finally, don’t forget to shutdown the debugger:

>>> gdb.shutdown()                  # byexample: +pass -skip

Install

Just run:

$ pip install python-gdb-ctrl         # byexample: +pass

You will find the python-gdb-ctrl package at PyPI

Hacking/Contributing

Go ahead! Clone the repository, do a small fix/enhancement, run make deps-dev to install the development dependencies including the test engine byexample, then run make test to ensure that everything is working as expected and finally propose your Pull Request!