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Pdb crashes after jump with Fatal Python error: _PyMem_DebugRawFree: bad trailing pad byte #91742
Description
Crash report
Access violation occurs when using pdb in the following procedure:
- step in a function
- step next a few lines inside print function
- before exiting print function, jump to the beginning of the code
- continue
__author__ = "pi"
__version__ = "3.14"
def about():
"""About"""
print(f"Module: {__file__!r}",
f"Author: {__author__!r}",
f"Version: {__version__!r}",
sep='\n')
breakpoint()
about()Error messages
$ python -Wd -Xdev -Xtracemalloc test_pdb.py
> test_pdb.py(12)<module>()
-> about()
(Pdb) s
--Call--
> test_pdb.py(4)about()
-> def about():
(Pdb) n
> test_pdb.py(6)about()
-> print(f"Module: {__file__!r}",
(Pdb) n
> test_pdb.py(7)about()
-> f"Author: {__author__!r}",
(Pdb) j 4
> test_pdb.py(4)about()
-> def about():
(Pdb) c
Module: 'test_pdb.py'
Author: 'pi'
Version: '3.14'
Debug memory block at address p=0000021D17AD8CF0: API 'o'
432 bytes originally requested
The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
The 8 pad bytes at tail=0000021D17AD8EA0 are not all FORBIDDENBYTE (0xfd):
at tail+0: 0x90 *** OUCH
at tail+1: 0x46 *** OUCH
at tail+2: 0x05 *** OUCH
at tail+3: 0x17 *** OUCH
at tail+4: 0x1d *** OUCH
at tail+5: 0x02 *** OUCH
at tail+6: 0x00 *** OUCH
at tail+7: 0x00 *** OUCH
Data at p: 00 00 00 00 00 00 00 00 ... f0 b4 b5 16 1d 02 00 00
Memory block allocated at (most recent call first):
File "test_pdb.py", line 12
Fatal Python error: _PyMem_DebugRawFree: bad trailing pad byte
Python runtime state: finalizing (tstate=0000021D169BEA10)
Current thread 0x000033f0 (most recent call first):
<no Python frame>
Your environment
- CPython versions tested on: 3.10.4
- Operating system and architecture: Windows10 64bit
Activity
dignissimus commented on Jun 21, 2022
Commit cf345e9 introduced this issue.
Running the following minimal example with the below input reproduces the crash.
dignissimus commented on Jun 21, 2022
PDB attempts to set f_lineno but in doing so it seems to try and de-allocate NULL.
cpython/Lib/pdb.py
Line 1172 in 4abab6b
cpython/Objects/frameobject.c
Lines 417 to 422 in 296e4ef
kumaraditya303 commented on Jun 22, 2022
Changing Py_DECREF to Py_XDECREF fixes the issue but I'll let @markshannon decide if it is the correct fix.
cc @markshannon
GDB backtrace:
markshannon commented on Jun 22, 2022
This looks like an old bug, probably dating back to the introduction of LOAD_METHOD.
LOAD_METHOD pushes a NULL to stack, which could cause this crash. LOAD_GLOBAL can also push a NULL, making this bug much easier to trigger.
@kumaraditya303 your fix looks correct.
GH-91742: Fix pdb crash after jump (GH-94171)
pythonGH-91742: Fix pdb crash after jump (pythonGH-94171)
[3.11] GH-91742: Fix pdb crash after jump (GH-94171) (#94176)
kumaraditya303 commented on Jun 24, 2022
Python 3.11 and 3.12 (main) both are fixed now.
However Python 3.10 is also affected but it crashes on different assertion.
python: Python/ceval.c:3040: _PyEval_EvalFrameDefault: Assertion `STACK_LEVEL() <= co->co_stacksize' failed.cc @markshannon
Revert 30935 defer bpo45162 to 312 (#94285)
pablogsal commented on Jun 27, 2022
Removing the 3.11 and 3.12 tags so these are fixed in 3.11 and 3.12.
pablogsal commented on Aug 2, 2022
I'm removing the release blocker flag because 3.10 was already crashing with this. This will be treated as a regular bugfix.
sunmy2019 commented on Jun 17, 2023
Closed as 3.10 is no longer accepting bug fixes