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Legacy tracing & PY_UNWIND: arg of legacy tracer call should be NULL #110892
Description
Bug report
Bug description:
When using a legacy tracer with PyEval_SetTrace and a function exits with an exception, the arg of the tracer event PyTrace_RETURN should be NULL docs. Currently in 3.12 (& 3.13), the arg is set to the exception value because the PY_UNWIND handler is forwarding its arg to the legacy tracer function.
CPython versions tested on:
3.12
Operating systems tested on:
No response
Activity
gaogaotiantian commentedon Oct 15, 2023
I'm confused. Why do you think the exception is passed to the legacy tracer? Could you share an example code?
In
_PyEval_SetTrace, the callback ofPY_MONITORING_EVENT_PY_UNWINDissys_trace_func3which unconditionally passesPy_Noneas the arg to the trace function. That is the case for both 3.12 and 3.13.jpe commentedon Oct 15, 2023
The arg needs to be NULL and not Py_None when there's an exception. For the legacy tracer 'r' event, the arg is the value returned so arg=Py_None indicates None is returned without an exception.
I found this while debugging Wing's debugger which uses a C implemented trace function and I saw the arg was not NULL and didn't look at what the value was or look closely up the stack; sorry. It may be that the trampoline that called a Python implemented trace function passed Py_None when arg was NULL, but it's been years since I worked with a Python implemented trace function.
gaogaotiantian commentedon Oct 15, 2023
Okay I think I understood what you were talking about.
gaogaotiantian commentedon Oct 15, 2023
PR is made to fix this.
jpe commentedon Oct 16, 2023
I've verified that the trace function gets a NULL on an UNWIND event with the PR. Thanks!
Shouldn't the profile function also get a NULL on an UNWIND event?
gaogaotiantian commentedon Oct 16, 2023
Yes,
sys_profile_unwindis changed to return NULL in the same PR.jpe commentedon Oct 17, 2023
I see the profile change now; LGTM.
gh-110892: Return NULL for `PyTrace_RETURN` events caused by an excep…
pythongh-110892: Return NULL for `PyTrace_RETURN` events caused by an…
pythongh-110892: Return NULL for `PyTrace_RETURN` events caused by an…
pythongh-110892: Return NULL for `PyTrace_RETURN` events caused by an…