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[WIP, DO NOT MERGE] bpo-41188: Prepare CPython for opague PyObject structure. #21262

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[WIP, DO NOT MERGE] bpo-41188: Prepare CPython for opague PyObject structure. #21262

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3d5826b
Added new type member 'tp_obj_offset'.
WildCard65 Jul 1, 2020
ff05339
Added static library "slib_pythoncore" to act as a medium between CPy…
WildCard65 Jul 1, 2020
8aa000e
Added basic implementation of "Py_TPFLAGS_OMIT_PYOBJECT_SIZE".
WildCard65 Jul 2, 2020
8774b02
Fixed GCC error
WildCard65 Jul 2, 2020
da3b98a
Add forgotten member documentation.
WildCard65 Jul 2, 2020
686d657
Trick PyObject into believing it's an opaque type.
WildCard65 Jul 2, 2020
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Trick PyObject into believing it's an opaque type.
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@WildCard65
WildCard65 committed Jul 2, 2020
commit 686d65745d3ad2f23fc980cfaab2bb4b56de5a92
52 changes: 36 additions & 16 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2086,13 +2086,19 @@ best_base(PyObject *bases)
return base;
}

#define GET_TYPE_TOTALSIZE(type) (_PyType_HasFeature(type, Py_TPFLAGS_OMIT_PYOBJECT_SIZE) ? type->tp_obj_size : type->tp_basicsize)
static inline const Py_ssize_t get_type_totalsize(PyTypeObject *type)
{
if (type->tp_obj_size < sizeof(PyObject)) // PyType_Type->tp_new manages to trigger this.
return type->tp_basicsize;

return type->tp_obj_size;
}

static int
extra_ivars(PyTypeObject *type, PyTypeObject *base)
{
size_t t_size = GET_TYPE_TOTALSIZE(type);
size_t b_size = GET_TYPE_TOTALSIZE(base);
size_t t_size = get_type_totalsize(type);
size_t b_size = get_type_totalsize(base);

assert(t_size >= b_size); /* Else type smaller than base! */
if (type->tp_itemsize || base->tp_itemsize) {
Expand Down Expand Up @@ -4848,7 +4854,7 @@ object___sizeof___impl(PyObject *self)
isize = Py_TYPE(self)->tp_itemsize;
if (isize > 0)
res = Py_SIZE(self) * isize;
res += GET_TYPE_TOTALSIZE(Py_TYPE(self));
res += get_type_totalsize(Py_TYPE(self));

return PyLong_FromSsize_t(res);
}
Expand Down Expand Up @@ -4947,7 +4953,8 @@ PyTypeObject PyBaseObject_Type = {
PyObject_GenericGetAttr, /* tp_getattro */
PyObject_GenericSetAttr, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | /* tp_flags */
Py_TPFLAGS_OMIT_PYOBJECT_SIZE,
object_doc, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
Expand Down Expand Up @@ -5366,7 +5373,29 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)

static int add_operators(PyTypeObject *);

#define SET_SPECIAL_TYPEVAR(var, value) *((Py_ssize_t *)&type->var) = value
void set_type_memory_data(PyTypeObject *type, PyTypeObject *base)
{
// Obtain the true size of the base type.
Py_ssize_t base_size = 0, base_offset = 0;
if (base != NULL) { // Only possible if we're not dealing with PyBaseObject_Type
if (_PyType_HasFeature(base, Py_TPFLAGS_OMIT_PYOBJECT_SIZE)) {
base_size = base->tp_obj_size;
base_offset = base->tp_obj_offset;
} else {
base_size = base->tp_basicsize;
base_offset = 0; // PyObject ALWAYS occupies the start of the memory block.
}
}

Py_ssize_t *size_ptr = (Py_ssize_t *)&type->tp_obj_size, *offset_ptr = (Py_ssize_t *)&type->tp_obj_offset;
if (_PyType_HasFeature(type, Py_TPFLAGS_OMIT_PYOBJECT_SIZE)) {
*size_ptr = base_size + type->tp_basicsize;
*offset_ptr = base_offset + base_size; // The type's internal structure occupies the next block of memory.
} else {
*size_ptr = type->tp_basicsize; // tp_basicsize already includes base_size.
*offset_ptr = 0; // The type's internal structure already includes "PyObject".
}
}

int
PyType_Ready(PyTypeObject *type)
Expand Down Expand Up @@ -5430,16 +5459,7 @@ PyType_Ready(PyTypeObject *type)
goto error;
}

if (type->tp_flags & Py_TPFLAGS_OMIT_PYOBJECT_SIZE) {
// tp_basicsize doesn't include the size of it's base type.
Py_ssize_t base_size = GET_TYPE_TOTALSIZE(base);

SET_SPECIAL_TYPEVAR(tp_obj_offset, (base->tp_obj_offset + base_size));
SET_SPECIAL_TYPEVAR(tp_obj_size, (base_size + type->tp_basicsize));
} else { // Type uses the size of PyObject, so the special variables are not used.
SET_SPECIAL_TYPEVAR(tp_obj_offset, 0);
SET_SPECIAL_TYPEVAR(tp_obj_size, 0);
}
set_type_memory_data(type, base);

/* Initialize ob_type if NULL. This means extensions that want to be
compilable separately on Windows can call PyType_Ready() instead of
Expand Down
2 changes: 1 addition & 1 deletion PC/pyconfig.h
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Original file line number Diff line number Diff line change
Expand Up @@ -276,7 +276,7 @@ Py_NO_ENABLE_SHARED to find out. Also support MS_NO_COREDLL for b/w compat */
# pragma comment(lib, "slib_python310_d.lib")
# pragma comment(lib,"python310_d.lib")
# elif defined(Py_LIMITED_API)
# pragma comment(lib, "slib_python3.lib")
# pragma comment(lib, "slib_python310.lib")
# pragma comment(lib,"python3.lib")
# else
# pragma comment(lib, "slib_python310.lib")
Expand Down