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[3.13] gh-130851: Only intern constants of types generated by the compiler (GH-130901) #130953

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colesbury merged 1 commit into from
Mar 8, 2025
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[3.13] gh-130851: Only intern constants of types generated by the compiler (GH-130901) #130953

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[3.13] gh-130851: Only intern constants of types generated by the com… 
…piler (GH-130901)

The free-threading build interns and immortalizes most constants
generated by the bytecode compiler. However, users can construct their
own code objects with arbitrary constants. We should not intern or
immortalize these objects if they are not of a type that we know how to
handle.

This change fixes a reference leak failure in the recently added
`test_code.test_unusual_constants` test. It also addresses a potential
crash that could occur when attempting to destroy an immortalized
object during interpreter shutdown.
(cherry picked from commit 12db452)

Co-authored-by: Sam Gross <colesbury@gmail.com>
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@colesbury
colesbury committed Mar 7, 2025
commit 2d72e4de194562d11a0fbc29a5869f083aa02568
36 changes: 34 additions & 2 deletions Objects/codeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -132,6 +132,38 @@ should_intern_string(PyObject *o)

#ifdef Py_GIL_DISABLED
static PyObject *intern_one_constant(PyObject *op);

// gh-130851: In the free threading build, we intern and immortalize most
// constants, except code objects. However, users can generate code objects
// with arbitrary co_consts. We don't want to immortalize or intern unexpected
// constants or tuples/sets containing unexpected constants.
static int
should_immortalize_constant(PyObject *v)
{
// Only immortalize containers if we've already immortalized all their
// elements.
if (PyTuple_CheckExact(v)) {
for (Py_ssize_t i = PyTuple_GET_SIZE(v); --i >= 0; ) {
if (!_Py_IsImmortal(PyTuple_GET_ITEM(v, i))) {
return 0;
}
}
return 1;
}
else if (PyFrozenSet_CheckExact(v)) {
PyObject *item;
Py_hash_t hash;
Py_ssize_t pos = 0;
while (_PySet_NextEntry(v, &pos, &item, &hash)) {
if (!_Py_IsImmortal(item)) {
return 0;
}
}
return 1;
}
return (PyLong_CheckExact(v) || PyFloat_CheckExact(v) ||
PyComplex_Check(v) || PyBytes_CheckExact(v));
}
#endif

static int
Expand Down Expand Up @@ -240,8 +272,8 @@ intern_constants(PyObject *tuple, int *modified)
// we are also immortalizing objects that use deferred reference
// counting.
PyThreadState *tstate = PyThreadState_GET();
if (!_Py_IsImmortal(v) && !PyCode_Check(v) &&
!PyUnicode_CheckExact(v) &&
if (!_Py_IsImmortal(v) && !PyUnicode_CheckExact(v) &&
should_immortalize_constant(v) &&
_Py_atomic_load_int(&tstate->interp->gc.immortalize) >= 0)
{
PyObject *interned = intern_one_constant(v);
Expand Down