bpo-38070: Enhance visit_decref() debug trace #16631
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subtract_refs() now pass the parent object to visit_decref() which pass it to _PyObject_ASSERT(). So if the "is freed" assertion fails, the parent is used in debug trace, rather than the freed object. The parent object is more likely to contain useful information. Freed objects cannot be inspected are are displayed as "<object at xxx is freed>" with no other detail.
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Example with https://bugs.python.org/issue38400 bug. Without the change, Python exit with: With this change, the output is more complete: In this case, the bug was that None was seen as freed: the None object can be easily be recovered using a debugger in the visit_decref() frame. |
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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.8. |
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Sorry, @vstinner, I could not cleanly backport this to |
vstinner
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* bpo-36389: _PyObject_CheckConsistency() available in release mode (GH-16612) bpo-36389, bpo-38376: The _PyObject_CheckConsistency() function is now also available in release mode. For example, it can be used to debug a crash in the visit_decref() function of the GC. Modify the following functions to also work in release mode: * _PyDict_CheckConsistency() * _PyObject_CheckConsistency() * _PyType_CheckConsistency() * _PyUnicode_CheckConsistency() Other changes: * _PyMem_IsPtrFreed(ptr) now also returns 1 if ptr is NULL (equals to 0). * _PyBytesWriter_CheckConsistency() now returns 1 and is only used with assert(). * Reorder _PyObject_Dump() to write safe fields first, and only attempt to render repr() at the end. (cherry picked from commit 6876257) * bpo-36389: Fix _PyBytesWriter in release mode (GH-16624) Fix _PyBytesWriter API when Python is built in release mode with assertions. (cherry picked from commit 60ec6ef) * bpo-38070: Enhance visit_decref() debug trace (GH-16631) subtract_refs() now pass the parent object to visit_decref() which pass it to _PyObject_ASSERT(). So if the "is freed" assertion fails, the parent is used in debug trace, rather than the freed object. The parent object is more likely to contain useful information. Freed objects cannot be inspected are are displayed as "<object at xxx is freed>" with no other detail. (cherry picked from commit 4d5f94b) * Fix also a typo in PYMEM_DEADBYTE macro comment * bpo-36389: Add newline to _PyObject_AssertFailed() (GH-16629) Add a newline between the verbose object dump and the Py_FatalError() logs for readability. (cherry picked from commit 7775349)
jacobneiltaylor
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Dec 5, 2019
subtract_refs() now pass the parent object to visit_decref() which pass it to _PyObject_ASSERT(). So if the "is freed" assertion fails, the parent is used in debug trace, rather than the freed object. The parent object is more likely to contain useful information. Freed objects cannot be inspected are are displayed as "<object at xxx is freed>" with no other detail.
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subtract_refs() now pass the parent object to visit_decref() which
pass it to _PyObject_ASSERT(). So if the "is freed" assertion fails,
the parent is used in debug trace, rather than the freed object. The
parent object is more likely to contain useful information. Freed
objects cannot be inspected are are displayed as "" with no other detail.
https://bugs.python.org/issue38070