PyObject_CallFunctionObjArgs segfaults

[Jen Kris]

Recently I completed a project where I used PyObject_CallFunctionObjArgs extensively with the NLTK library from a program written in NASM, with no problems.  Now I am on a new project where I call the Python random library.  I use the same setup as before, but I am getting a segfault with random.seed.  

At the start of the NASM program I call a C API program that gets PyObject pointers to “seed” and “randrange” in the same way as I did before:

int64_t Get_LibModules(int64_t * return_array)
{
PyObject * pName_random = PyUnicode_FromString("random");
PyObject * pMod_random = PyImport_Import(pName_random);

if (pMod_random == 0x0){
PyErr_Print();
return 1;}

PyObject * pAttr_seed = PyObject_GetAttrString(pMod_random, "seed");
PyObject * pAttr_randrange = PyObject_GetAttrString(pMod_random, "randrange");

return_array[0] = (int64_t)pAttr_seed;
return_array[1] = (int64_t)pAttr_randrange;

return 0;
}

Later in the same program I call a C API program to call random.seed:

int64_t C_API_2(PyObject * pAttr_seed, Py_ssize_t value_1)
{
PyObject * p_seed_calc = PyObject_CallFunctionObjArgs(pAttr_seed, value_1);

if (p_seed_calc == 0x0){
    PyErr_Print();
    return 1;}

//Prepare return values
long return_val = PyLong_AsLong(p_seed_calc);

return return_val;
}

The first program correctly imports “random” and gets pointers to “seed” and “randrange.”  I verified that the same pointer is correctly passed into C_API_2, and the seed value (1234) is passed as  Py_ssize_t value_1.  But I get this segfault:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff64858d5 in _Py_INCREF (op=0x4d2) at ../Include/object.h:459
459     ../Include/object.h: No such file or directory.

So I tried Py_INCREF in the first program: 

Py_INCREF(pMod_random);
Py_INCREF(pAttr_seed);

Then I moved Py_INCREF(pAttr_seed) to the second program.  Same segfault.

Finally, I initialized “random” and “seed” in the second program, where they are used.  Same segfault. 

The segfault refers to Py_INCREF, so this seems to do with reference counting, but Py_INCREF didn’t solve it.   

I’m using Python 3.8 on Ubuntu. 

Thanks for any ideas on how to solve this. 

Jen