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gh-112529: Remove PyGC_Head from object pre-header in free-threaded build (#114564)

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* gh-112529: Remove PyGC_Head from object pre-header in free-threaded build

This avoids allocating space for PyGC_Head in the free-threaded build.
The GC implementation for free-threaded CPython does not use the
PyGC_Head structure.

 * The trashcan mechanism uses the `ob_tid` field instead of `_gc_prev`
   in the free-threaded build.
 * The GDB libpython.py file now determines the offset of the managed
   dict field based on whether the running process is a free-threaded
   build. Those are identified by the `ob_ref_local` field in PyObject.
 * Fixes `_PySys_GetSizeOf()` which incorrectly incorrectly included the
   size of `PyGC_Head` in the size of static `PyTypeObject`.
This commit is contained in:
Sam Gross 2024-02-01 15:29:19 -05:00 • committed by GitHub
parent 500ede0117
commit 587d480203
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GPG key ID: B5690EEEBB952194
9 changed files with 86 additions and 26 deletions
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15
Tools/gdb/libpython.py
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@ -70,6 +70,14 @@ def _type_unsigned_int_ptr():
def _sizeof_void_p():
return gdb.lookup_type('void').pointer().sizeof
def _managed_dict_offset():
# See pycore_object.h
pyobj = gdb.lookup_type("PyObject")
if any(field.name == "ob_ref_local" for field in pyobj.fields()):
return -1 * _sizeof_void_p()
else:
return -3 * _sizeof_void_p()
Py_TPFLAGS_MANAGED_DICT = (1 << 4)
Py_TPFLAGS_HEAPTYPE = (1 << 9)
@ -457,7 +465,7 @@ class HeapTypeObjectPtr(PyObjectPtr):
if dictoffset < 0:
if int_from_int(typeobj.field('tp_flags')) & Py_TPFLAGS_MANAGED_DICT:
assert dictoffset == -1
dictoffset = -3 * _sizeof_void_p()
dictoffset = _managed_dict_offset()
else:
type_PyVarObject_ptr = gdb.lookup_type('PyVarObject').pointer()
tsize = int_from_int(self._gdbval.cast(type_PyVarObject_ptr)['ob_size'])
@ -485,9 +493,8 @@ class HeapTypeObjectPtr(PyObjectPtr):
has_values = int_from_int(typeobj.field('tp_flags')) & Py_TPFLAGS_MANAGED_DICT
if not has_values:
return None
charptrptr_t = _type_char_ptr().pointer()
ptr = self._gdbval.cast(charptrptr_t) - 3
char_ptr = ptr.dereference()
ptr = self._gdbval.cast(_type_char_ptr()) + _managed_dict_offset()
char_ptr = ptr.cast(_type_char_ptr().pointer()).dereference()
if (int(char_ptr) & 1) == 0:
return None
char_ptr += 1