segfault/debug abort from `perf_map_write_entry` with lone surrogate in filename or qualname

Crash report

What happened?

import sys
import sysconfig
import types

assert not sysconfig.get_config_var("PY_HAVE_PERF_TRAMPOLINE")
sys.activate_stack_trampoline("perf")
code = compile("pass", "bad\ud800file", "exec")
eval(code)

python3: Python/generated_cases.c.h:13862: PyObject *_PyEval_EvalFrameDefault(PyThreadState *, _PyInterpreterFrame *, int): Assertion `!_PyErr_Occurred(tstate)' failed.
Aborted

perf_map_write_entry does not check that the calls to PyUnicde_AsUTF8 succeed, resulting in null pointers being passed to snprintf. This is UB, and may crash in some libc versions, or may be replaced with a placeholder value.

Regardless, a failed conversion leaves a stale exception around, which then will trigger a debug abort a bit later (in debug builds):

https://github.com/python/cpython/blob/e8158d1a02d6e5e974d4dbc0633b6a3ad960d7a3/Python/perf_trampoline.c#L251-L262

Seems trivial to check the result value here. I notice that perf_jit_trampoline (similar code) uses a common helper function that checks the values and replaces them with "" if NULL

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.16.0a0 (heads/main-dirty:20e6c2f, Aug 19 2026, 15:22:30) [Clang 22.1.8 ]

Linked PRs

• gh-156300
• gh-157773
• gh-157774

Start in Python/perf_trampoline.c at perf_map_write_entry and compare its conversion handling with the shared helper used by perf_jit_trampoline. Reproduce the report with the lone-surrogate filename example, then verify that the conversion failure no longer leaves a stale exception or causes an abort; linked PRs indicate this work is already underway.