PyObject_CallFunctionObjArgs segfaults

[MRAB]

On 2022-09-29 16:54, Jen Kris via Python-list wrote:
> 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);
> 
Both PyUnicode_FromString and PyImport_Import return new references or 
null pointers.

> if (pMod_random == 0x0){
> PyErr_Print();

You're leaking a reference here (pName_random).

> 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;
> 

You're leaking 2 references here (pName_random and pMod_random).

> 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);

It's expecting all of the arguments to be PyObject*, but value_1 is 
Py_ssize_t instead of PyObject* (a pointer to a _Python_ int).

The argument list must end with a null pointer.

It returns a new reference or a null pointer.

> 
> if (p_seed_calc == 0x0){
>      PyErr_Print();
>      return 1;}
> 
> //Prepare return values
> long return_val = PyLong_AsLong(p_seed_calc);
> 
You're leaking a reference here (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
>