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GH-118074: Executors in the COLD_EXITS array are not GC'able #118117

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Merged
merged 4 commits into from
Apr 22, 2024
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GH-118074: Executors in the COLD_EXITS array are not GC'able #118117

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f2e10eb
Executors in the COLD_EXITS array are not GC'able
gvanrossum Apr 20, 2024
e748e8a
Fix address arithmetic bug
gvanrossum Apr 20, 2024
bb71ae9
Use correct COLD_EXITS upper bound
gvanrossum Apr 22, 2024
1653fe5
Add blurb
gvanrossum Apr 22, 2024
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2024-04-22-08-34-28.gh-issue-118074.5_JnIa.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Make sure that the Executor objects in the COLD_EXITS array aren't assumed
to be GC-able (which would access bytes outside the object).
10 changes: 10 additions & 0 deletions Python/optimizer.c
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Expand Up @@ -394,6 +394,15 @@ executor_traverse(PyObject *o, visitproc visit, void *arg)
return 0;
}

static int
executor_is_gc(PyObject *o)
{
if ((PyObject *)&COLD_EXITS[0] <= o && o < (PyObject *)&COLD_EXITS[COLD_EXIT_COUNT]) {
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@markshannon markshannon Apr 23, 2024

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This is undefined behavior in C. Although it will mostly work in practice.

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@gvanrossum gvanrossum Apr 23, 2024

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So I take it this should work?

Suggested change
if ((PyObject *)&COLD_EXITS[0] <= o && o < (PyObject *)&COLD_EXITS[COLD_EXIT_COUNT]) {
if (_Py_IsImmortal(o)) {

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@markshannon markshannon Apr 23, 2024

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Yes

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@gvanrossum gvanrossum Apr 23, 2024

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Maybe add a similar thing to the top of executor_traverse()? (Although, really, cold exits don't have exits, so their exit_count should always be zero, right? So why bother.

Anyway, see gh-118182 for a fix.

return 0;
}
return 1;
}

PyTypeObject _PyUOpExecutor_Type = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
.tp_name = "uop_executor",
Expand All @@ -405,6 +414,7 @@ PyTypeObject _PyUOpExecutor_Type = {
.tp_methods = executor_methods,
.tp_traverse = executor_traverse,
.tp_clear = executor_clear,
.tp_is_gc = executor_is_gc,
};

/* TO DO -- Generate these tables */
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