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bpo-37138: fix undefined behaviour with memcpy() on NULL array #13867

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Merged
gpshead merged 1 commit into from
Jun 7, 2019
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bpo-37138: fix undefined behaviour with memcpy() on NULL array #13867

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6 changes: 5 additions & 1 deletion Objects/classobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,11 @@ method_vectorcall(PyObject *method, PyObject *const *args,
}
/* use borrowed references */
newargs[0] = self;
memcpy(newargs + 1, args, totalargs * sizeof(PyObject *));
if (totalargs) { /* bpo-37138: if totalargs == 0, then args may be

@vstinner vstinner Jun 7, 2019

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I don't think that the comment is required.

@gpshead: what do you think?

@jdemeyer jdemeyer Jun 7, 2019

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I wrote the comment because the reason for that if (totalargs) is totally not obvious. It's an obscure point in the C standard that I was unaware of. I think that there are plenty of developers that do not know that memcpy(dst, NULL, 0) is undefined behaviour.

@gpshead gpshead Jun 7, 2019

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I'm in favor of such comments. :)

* NULL and calling memcpy() with a NULL pointer
* is undefined behaviour. */
memcpy(newargs + 1, args, totalargs * sizeof(PyObject *));
}
result = _PyObject_Vectorcall(func, newargs, nargs+1, kwnames);
PyMem_Free(newargs);
}
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