Bug#684214: gcc-4.7: Fail to build functional python/numpy extension

[Raphael Plasson <rplasson@gmail.com>]

Package: gcc-4.7
Version: 4.7.1-6
Severity: normal


When building a C extension to Python that uses Numpy (more precisely that tries
to access a Numpy array from C), the resulting module segfaults when used. I
spent some time figuring out what was the origin of the problem (similar extension
I wrote did work in the past), and the problem is solved when compiling the 
module with olde gcc version (both gcc-4.5 and gcc-4.6 did build functional modules,
I couldn't install older version of gcc-4.7 for further testing), so I assume there 
is a problem with this version for compiling numpy modules.

Here is an minimal example, I hope it can reproduce the bug (and that the fault is 
not from my code, sorry if it is the case...). It works correctly when compiled 
with gcc-4.[56], and segfaults when compiled with gcc-4.7. It can be compiled by:
gcc-4.[5-7] -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c essai.c -o essai.o -march=native -g0
gcc-4.[5-7] -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro essai.o -o essai.so
(the compile options are as automatically generated by distutils stuff).

For testing it, you can simply do on a python shell:
>>> from essai import func
>>> import numpy as N
>>> x = N.zeros((10,10))+1.
>>> func(x,4)
It should return 25.25. It segfaults during the PyArray_ContiguousFromObject call (when 
getting access to the numpy array from C).

Here is the code:
#include <Python.h>
#include <stdio.h>
#include <numpy/arrayobject.h>

static char func_doc[] = "func(data, val)\n";

static PyObject* func(PyObject *self, PyObject *args)
{
    PyObject *input;
    PyArrayObject *data;
    double res=1.;
    int val;
    int i,j;

    if (!PyArg_ParseTuple(args, "Ol", &input, &val)) return NULL;
    data = (PyArrayObject *) PyArray_ContiguousFromObject(input, PyArray_DOUBLE, 2, 2);
    if (data == NULL) return NULL;

    for (i = 0; i < (int) data->dimensions[0]; ++i)
    	for (j = 0; j < (int) data->dimensions[1]; ++j)
	    res += ((double *)data->data)[i + j*data->dimensions[0]];

    res /= val;
    return Py_BuildValue("d", res);
}

static PyMethodDef module_methods[] = {
    {"func", func, METH_VARARGS, func_doc},
    {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC initessai(void)
{
    Py_InitModule("essai", module_methods);
    import_array();
}




-- System Information:
Debian Release: wheezy/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.4-trunk-amd64 (SMP w/24 CPU cores)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages gcc-4.7 depends on:
ii  binutils      2.22-7.1
ii  cpp-4.7       4.7.1-6
ii  gcc-4.7-base  4.7.1-6
ii  libc6         2.13-35
ii  libgcc1       1:4.7.1-6
ii  libgmp10      2:5.0.5+dfsg-2
ii  libgomp1      4.7.1-6
ii  libitm1       4.7.1-6
ii  libmpc2       0.9-4
ii  libmpfr4      3.1.0-5
ii  libquadmath0  4.7.1-6
ii  zlib1g        1:1.2.7.dfsg-13

Versions of packages gcc-4.7 recommends:
ii  libc6-dev  2.13-35

Versions of packages gcc-4.7 suggests:
pn  binutils-gold        <none>
pn  gcc-4.7-doc          <none>
pn  gcc-4.7-locales      <none>
ii  gcc-4.7-multilib     4.7.1-6
pn  libgcc1-dbg          <none>
pn  libgomp1-dbg         <none>
pn  libitm1-dbg          <none>
pn  libmudflap0-4.7-dev  <none>
pn  libmudflap0-dbg      <none>
pn  libquadmath0-dbg     <none>

-- no debconf information