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

Python/perf_trampoline.c の perf_map_write_entry から始め、perf_jit_trampoline が使用する共有ヘルパーと変換処理を比較してください。lone surrogate を含むファイル名の例で報告を再現し、その後、変換失敗によって stale exception が残ったり abort が発生したりしないことを確認してください。リンクされた PR は、この作業がすでに進行中であることを示しています。