cygdb-demo

Example of debugging Cython project

Install dependencies

Set-up environment, for example using vagrant

$ vagrant init debian/jessie64
$ vagrant up
$ vagrant ssh

$ sudo apt-get install build-essential python-dbg git gdb \
                       python-setuptools python-pip python-dev

$ sudo /usr/bin/python-dbg /usr/bin/pip install cython

Check version and configuation

$ python-dbg --version
Python 2.7.9


$ python --version
Python 2.7.9


$ python3
-bash: python3: command not found


$ cython --version
Cython version 0.25.2
[89796 refs]


$ gdb --version
GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".


$ gdb --configuration
This GDB was configured as follows:
    configure --host=x86_64-linux-gnu --target=x86_64-linux-gnu
              --with-auto-load-dir=$debugdir:$datadir/auto-load
              --with-auto-load-safe-path=$debugdir:$datadir/auto-load
              --with-expat
              --with-gdb-datadir=/usr/share/gdb (relocatable)
              --with-jit-reader-dir=/usr/lib/gdb (relocatable)
              --without-libunwind-ia64
              --with-lzma
              --with-python=/usr (relocatable)
              --with-separate-debug-dir=/usr/lib/debug (relocatable)
              --with-system-gdbinit=/etc/gdb/gdbinit
              --with-zlib
              --without-babeltrace
("Relocatable" means the directory can be moved with the GDB installation
tree, and GDB will still find it.)

build

Get the source code:

git clone https://github.com/dfroger/cygdb-demo
cd cygdb-demo

Build:

python-dbg setup.py build_ext --inplace

demo.c and debug infos

demo.pyx compiles to demo.c and cython_debug/cython_debug_info_demo

For readiblity, cython_debug_info_demo has been formatted bellow with:

sudo apt-get install libxml2-utils
xmllint --format --recover cython_debug_info_demo > out.xml

cdef

cdef double foo(double x):
    return 2*x

compiles to:

static double __pyx_f_4demo_foo(double __pyx_v_x)

debug info:

<Function cname="__pyx_f_4demo_foo" lineno="1" name="foo" pf_cname="" qualified_name="demo.foo">
  <Locals>
    <LocalVar cname="__pyx_v_x" lineno="1" name="x" qualified_name="demo.foo.x" type="CObject"/>
  </Locals>
  <Arguments>
    <x/>
  </Arguments>
  <StepIntoFunctions/>
</Function>

def

def bar(double x):
    return 2*x

compiles to:

static PyObject *__pyx_pw_4demo_1bar(PyObject *__pyx_self, PyObject *__pyx_arg_x)
static PyObject *__pyx_pf_4demo_bar(CYTHON_UNUSED PyObject *__pyx_self, double __pyx_v_x)

debug info:

<Function cname="__pyx_pw_4demo_1bar" lineno="4" name="bar" pf_cname="" qualified_name="demo.bar">
  <Locals>
    <LocalVar cname="__pyx_v_x" lineno="4" name="x" qualified_name="demo.bar.x" type="CObject"/>
  </Locals>
  <Arguments/>
  <StepIntoFunctions/>
</Function>

cpdef

cpdef double baz(double x):
    return 2*x

compiles to:

static PyObject *__pyx_pw_4demo_3baz(PyObject *__pyx_self, PyObject *__pyx_arg_x)
static PyObject *__pyx_pf_4demo_2baz(CYTHON_UNUSED PyObject *__pyx_self, double __pyx_v_x)
static double __pyx_f_4demo_baz(double, int __pyx_skip_dispatch)

debug info:

<Function cname="__pyx_f_4demo_baz" lineno="7" name="baz" pf_cname="__pyx_pw_4demo_3baz" qualified_name="demo.baz">
  <Locals>
    <LocalVar cname="__pyx_v_x" lineno="7" name="x" qualified_name="demo.baz.x" type="CObject"/>
  </Locals>
  <Arguments>
    <x/>
  </Arguments>
  <StepIntoFunctions/>
</Function>

Demo of using cygdb

Run debugger:

$ cygdb . -- --args python-dbg main.py

Set up a breakpoint, and run:

cy break foo

cy run

cy list