How to use gdb python debugging extension inside virtualenv

Question

I'm running ubuntu, and installed the python-dbg package. When trying to use the installed version directly everything works great:

$ gdb python2.7-dbg
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
---x snipped x---
Reading symbols from /usr/bin/python2.7-dbg...done.
(gdb) r
Starting program: /usr/bin/python2.7-dbg
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Python 2.7.3 (default, Feb 27 2014, 19:39:25)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
Program received signal SIGINT, Interrupt.
0x00007ffff6997743 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:82
82      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) py-bt (<--- works, just has nothing to do)
(gdb)

So, I've been building a virtualenv using the package's binary python2.7-dbg (since some libraries need recompiling), using this command line:

~$ virtualenv ved -p /usr/bin/python2.7-dbg

Its all working fine, but when I'm using gdb inside the virtualenv, atleast the python pretty printers stop working:

~$ . ved/bin/activate
(ved)~$ gdb python
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
---x snipped x---
Reading symbols from /home/itai/ved/bin/python...done.
(gdb) r
Starting program: /home/itai/ved/bin/python
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Python 2.7.3 (default, Feb 27 2014, 19:39:25)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
Program received signal SIGINT, Interrupt.
0x00007ffff6997743 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:82
82      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) py-bt
Undefined command: "py-bt".  Try "help". (<---- PROBLEM)
(gdb)

Am I missing something within my virtualenv?

Answer 1

I've solved the problem by using strace on gdb, grepping the "open" syscalls.

It seems that gdb makes a search for python-gdb.py in several paths it guesses (according to the python binary), and whenever the file is not found it just fails silently.

Eventually the way to solve the problem is to link /usr/lib/debug/usr/bin/python2.7-gdb.py into the env's bin directory. The name of the link should be <python binary name>-gdb.py, being in my case python2.7-dbg-gdb.py (...).

After that, everything seems to work.

Answer 2

@itai's answer only partially worked for me on Ubuntu Trusty (14.04). I found a couple of other things worked better:

sudo apt-get install python2.7-dbg

then, in the virtualenv:

. bin/activate
mkdir bin/.debug
ln -s /usr/lib/debug/usr/bin/python2.7-gdb.py bin/.debug/python-gdb.py
ln -s /usr/lib/debug/usr/bin/python2.7 bin/.debug/

gdb --args bin/python2.7 ...

This helped gdb find the python debugging symbols as well as the py-bt etc commands.