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GH-133932: Tagged ints are heap safe #134244

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Merged
merged 2 commits into from
May 22, 2025
Merged

GH-133932: Tagged ints are heap safe #134244

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adaaa26
Tagged ints are heap safe
markshannon May 19, 2025
9eca136
Fix free-threaded macro
markshannon May 19, 2025
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20 changes: 7 additions & 13 deletions Include/internal/pycore_stackref.h
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Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,7 @@ PyStackRef_IsNullOrInt(_PyStackRef ref);
#else

#define Py_INT_TAG 3
#define Py_TAG_REFCNT 1

static inline bool
PyStackRef_IsTaggedInt(_PyStackRef i)
Expand All @@ -264,7 +265,7 @@ PyStackRef_UntagInt(_PyStackRef i)

#ifdef Py_GIL_DISABLED

#define Py_TAG_DEFERRED (1)
#define Py_TAG_DEFERRED Py_TAG_REFCNT

#define Py_TAG_PTR ((uintptr_t)0)
#define Py_TAG_BITS ((uintptr_t)1)
Expand Down Expand Up @@ -443,14 +444,13 @@ PyStackRef_AsStrongReference(_PyStackRef stackref)
/* References to immortal objects always have their tag bit set to Py_TAG_REFCNT
* as they can (must) have their reclamation deferred */

#define Py_TAG_BITS 1
#define Py_TAG_REFCNT 1
#define Py_TAG_BITS 3
#if _Py_IMMORTAL_FLAGS != Py_TAG_REFCNT
# error "_Py_IMMORTAL_FLAGS != Py_TAG_REFCNT"
#endif

#define BITS_TO_PTR(REF) ((PyObject *)((REF).bits))
#define BITS_TO_PTR_MASKED(REF) ((PyObject *)(((REF).bits) & (~Py_TAG_BITS)))
#define BITS_TO_PTR_MASKED(REF) ((PyObject *)(((REF).bits) & (~Py_TAG_REFCNT)))

#define PyStackRef_NULL_BITS Py_TAG_REFCNT
static const _PyStackRef PyStackRef_NULL = { .bits = PyStackRef_NULL_BITS };
Expand Down Expand Up @@ -530,7 +530,7 @@ PyStackRef_FromPyObjectSteal(PyObject *obj)
{
assert(obj != NULL);
#if SIZEOF_VOID_P > 4
unsigned int tag = obj->ob_flags & Py_TAG_BITS;
unsigned int tag = obj->ob_flags & Py_TAG_REFCNT;
#else
unsigned int tag = _Py_IsImmortal(obj) ? Py_TAG_REFCNT : 0;
#endif
Expand All @@ -549,12 +549,6 @@ PyStackRef_FromPyObjectStealMortal(PyObject *obj)
return ref;
}

// Check if a stackref is exactly the same as another stackref, including the
// the deferred bit. This can only be used safely if you know that the deferred
// bits of `a` and `b` match.
#define PyStackRef_IsExactly(a, b) \
(assert(((a).bits & Py_TAG_BITS) == ((b).bits & Py_TAG_BITS)), (a).bits == (b).bits)

static inline _PyStackRef
_PyStackRef_FromPyObjectNew(PyObject *obj)
{
Expand Down Expand Up @@ -607,7 +601,7 @@ PyStackRef_DUP(_PyStackRef ref)
static inline bool
PyStackRef_IsHeapSafe(_PyStackRef ref)
{
return (ref.bits & Py_TAG_BITS) == 0 || ref.bits == PyStackRef_NULL_BITS || _Py_IsImmortal(BITS_TO_PTR_MASKED(ref));
return (ref.bits & Py_TAG_BITS) != Py_TAG_REFCNT || ref.bits == PyStackRef_NULL_BITS || _Py_IsImmortal(BITS_TO_PTR_MASKED(ref));
}

static inline _PyStackRef
Expand Down Expand Up @@ -682,7 +676,7 @@ PyStackRef_XCLOSE(_PyStackRef ref)

// Note: this is a macro because MSVC (Windows) has trouble inlining it.

#define PyStackRef_Is(a, b) (((a).bits & (~Py_TAG_BITS)) == ((b).bits & (~Py_TAG_BITS)))
#define PyStackRef_Is(a, b) (((a).bits & (~Py_TAG_REFCNT)) == ((b).bits & (~Py_TAG_REFCNT)))


#endif // !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)
Expand Down
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