In unicodeobject.c and stringlib aligned addresses and sizes are used for optimization. pointer->integer and implicit integer->integer conversions may overflow or underflow on platforms with sizeof(size_t) != sizeof(void *) or sizeof(size_t) != sizeof(int). The proposed patch fixes such unsafe things in unicodeobject.c, stringlib and some other files.

There are still a few unsafe places in libffi, but in this library Py_uintptr_t nor uintptr_t are not available.