On 2022-09-29 21:47, Jen Kris wrote:
> To update my previous email, I found the problem, but I have a new
> problem.
>
> Previously I cast PyObject * value_ptr = (PyObject * )value_1 but
> that's not correct.  Instead I used PyObject * value_ptr =
> PyLong_FromLong(value_1) and that works.  HOWEVER, while
> PyObject_CallFunctionObjArgs does work now, it returns -1, which is
> not the right answer for random.seed.  I use "long return_val =
> PyLong_AsLong(p_seed_calc);" to convert it to a long.
>
random.seed returns None, so when you call PyObject_CallFunctionObjArgs
it returns a new reference to Py_None.

If you then pass to PyLong_AsLong a reference to something that's not a
PyLong, it'll set an error and return -1.

> So my question is why do I get -1 as return value?  When I query
> p_seed calc : get:
>
> (gdb) p p_seed_calc
> $2 = (PyObject *) 0x7ffff69be120 <_Py_NoneStruct>
>
Exactly. It's Py_None, not a PyLong.
> Thanks again.
>
> Jen
>
>
>
>
> Sep 29, 2022, 13:02 by python-list@python.org:
>
> Thanks very much to @MRAB for taking time to answer.  I changed my
> code to conform to your answer (as best I understand your comments
> on references), but I still get the same error.  My comments
> continue below the new code immediately below.
>
> int64_t Get_LibModules(int64_t * return_array)
> {
> PyObject * pName_random = PyUnicode_FromString("random");
> PyObject * pMod_random = PyImport_Import(pName_random);
>
> Py_INCREF(pName_random);
> Py_INCREF(pMod_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");
>
> Py_INCREF(pAttr_seed);
> Py_INCREF(pAttr_randrange);
>
> return_array[0] = (int64_t)pAttr_seed;
> return_array[1] = (int64_t)pAttr_randrange;
>
> return 0;
> }
>
> int64_t C_API_2(PyObject * pAttr_seed, Py_ssize_t value_1)
> {
> PyObject * value_ptr = (PyObject * )value_1;
> PyObject * p_seed_calc = PyObject_CallFunctionObjArgs(pAttr_seed,
> value_ptr, NULL);
>
> if (p_seed_calc == 0x0){
>     PyErr_Print();
>     return 1;}
>
> //Prepare return values
> long return_val = PyLong_AsLong(p_seed_calc);
>
> return return_val;
> }
>
> So I incremented the reference to all objects in Get_LibModules,
> but I still get the same segfault at
> PyObject_CallFunctionObjArgs.  Unfortunately, reference counting
> is not well documented so I’m not clear what’s wrong.
>
>
>
>
> Sep 29, 2022, 10:06 by python@mrabarnett.plus.com:
>
> 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
>
>
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>
>
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>