Glibc with debug symbols
The first issue I run into is that Valgrind refused to work if Glibc was not compiled with debug symbols.
This is how I did in my Gentoo notebook, I edited the /etc/make.conf file to enable the splitdebug feature:
Then re-emerged the glibc:
$ sudo emerge glibc
Then commented out the splitdebug feature to avoid emerging other packages with debug symbols (there is likely a better way to do this).
The big problem is that running Valgrind with a Python C extension raises tons of false positives. There are a number of things you need to do to avoid all these false positives.
The first one is to use latest version of Valgrind 3.7, because of some bug I forgot about present in version 3.6
Python, compiling for a memory debugger
Now, you need to install a version of Python to be used with Valgrind. There is one little change to do regarding an standard Python, edit file Objects/obmalloc.c and define Py_USING_MEMORY_DEBUGGER :
Now install as usual:
$ ./configure --prefix=~/Python-2.7.3-mem-debug
$ make install
The suppression file
Now you need to use the suppression file that you will find in the Python sources, at Misc/valgrind-python.supp. This is how I run the unit tests in pygit2 to find issues:
$ valgrind --trace-children=yes --suppressions=valgrind-python.supp \
~/Python-2.7.3-mem-debug/bin/python setup.py test