STINNER Victor <vstin...@python.org> added the comment:
Christian Tismer: "What about an even more flexible solution? A debug option
could memorize always the last object deallocated and give full info (the
object's repr) before the crash would happen."
Bugs in object_dealloc() are rare. Apart None, True and False, do you know
other objects which must not be deleted?
Calling repr(obj) can crash during late Python finalization for many reasons.
It is slow and can consume significant memory. Not all object types detect
loops (a container storing indirectly itself) and so it can fail with a
MemoryError: repr() is not "safe".
Using gdb, it is easy to dump the object currently being deleted: go the
object_dealloc() frame and use "print self" command.
Example using attached os_uname_refcount_bug.patch:
------------
$ gdb ./python
(...)
(gdb) run
>>> import os; os.uname()
>>> exit()
Debug memory block at address p=0x886e60: API ''
0 bytes originally requested
The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfd):
at p-7: 0x00 *** OUCH
at p-6: 0x00 *** OUCH
at p-5: 0x00 *** OUCH
at p-4: 0x00 *** OUCH
at p-3: 0x00 *** OUCH
at p-2: 0x00 *** OUCH
at p-1: 0x00 *** OUCH
Because memory is corrupted at the start, the count of bytes requested
may be bogus, and checking the trailing pad bytes may segfault.
The 8 pad bytes at tail=0x886e60 are not all FORBIDDENBYTE (0xfd):
at tail+0: 0x00 *** OUCH
at tail+1: 0x00 *** OUCH
at tail+2: 0x00 *** OUCH
at tail+3: 0x00 *** OUCH
at tail+4: 0x00 *** OUCH
at tail+5: 0x00 *** OUCH
at tail+6: 0x00 *** OUCH
at tail+7: 0x00 *** OUCH
Enable tracemalloc to get the memory block allocation traceback
Fatal Python error: _PyMem_DebugRawFree: bad ID: Allocated using API '',
verified using API 'o'
Python runtime state: finalizing (tstate=0x00000000008e1a80)
Current thread 0x00007ffff7c24740 (most recent call first):
Garbage-collecting
<no Python frame>
Program received signal SIGABRT, Aborted.
0x00007ffff7c662a2 in raise () from /lib64/libc.so.6
(...)
(gdb) frame 9
#9 0x0000000000499dd7 in object_dealloc (self=True)
at Objects/typeobject.c:4497
4497 Py_TYPE(self)->tp_free(self);
(gdb) print self
$2 = True
------------
----------
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue45061>
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