Debugging Extension Modules on Linux/Unix

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The first step in debugging C/C++ modules with gdb is to make sure that you are using a version of Python that was compiled with debug symbols. To do this, you need a source distribution of Python and you need to configure the distribution as described in the accompanying README.rst file.

In most cases, this can be done as follows: (1) Type ./configure, (2) type make OPT=-g, and (3) type make. Once the build is complete you can optionally install it with make install or just run Python in place without installing it.

When this is complete, compile your extension module against that version of Python.

Starting Debug

In order to run code both within Wing's Python debugger and gdb, launch your debug process from Wing first, then note the process ID shown in the tooltip that appears when you hover the mouse over the debug icon in the lower left of Wing's main window.

Next, start gdb and type attach <pid> where <pid> is replaced with the process ID reported by Wing. This will pause the process as it attaches, which gives you a chance to set breakpoints. When you're ready to continue the process, type c in gdb.

You are now debugging both at the Python and C/C++ level. You should be able to pause, step, and view data in Wing whenever gdb is not paused. When gdb is paused, Wing's debugger cannot be used until the process is continued at the gdb level.

Tips and Tricks

  • Misc/gdbinit in the Python source distribution contains useful macros for inspecting Python code from gdb. For example, pystack will print the Python stack, pylocals will print the Python locals, and pyframe prints the current Python stack frame. To use it, copy it into your ~/.gdbinit.
  • The following works to view Python data in PyObject * obj:

    (gdb) p PyObject_Print (obj, stderr, 0)
  • Breakpoints in a shared library cannot be set until after the shared library is loaded. ^C^C can be used to interrupt the debug process, set breakpoints, and then continue.
  • If LD_LIBRARY_PATH or other environment is not set as expected, check whether it is set in .cshrc. This file is read each time gdb runs so may overwrite your value. To work around this, set LD_LIBRARY_PATH in .profile instead. This file is read only once at login time.

See Debugging with Gdb for more information.