dtrace: debug abort importing module with lone surrogate unicode char in name while DTrace import probe is active

Crash report

What happened?

This one is a bit niche! It also needs a python compiled with --with-dtrace

probe.d:

python$target:::import-find-load-start
{
    printf("import probe fired\n");
}

test.py:

try:
  __import__('\ud800')
except:
  pass

> sudo dtrace -q -s probe.d -c './python.exe test.py'

Assertion failed: (!_PyErr_Occurred(tstate)), function _PyEval_EvalFrameDefault, file generated_cases.c.h, line 13858.
import probe fired
import probe fired
import probe fired
...

The import dtrace hooks pass call PyUnicode_AsUTF8 and pass the value to the probe without checking if the conversion succeeded, now dtrace doesn't seem to mind getting a null pointer (I don't know much about how that bit works tbh), but a stale exception is left around which triggers a debug assert:

https://github.com/python/cpython/blob/e8158d1a02d6e5e974d4dbc0633b6a3ad960d7a3/Python/import.c#L4106-L4107

[!CAUTION]
EDIT: I found some more cases of drace code doing the same, This isn't just limited to import machinery:
https://github.com/python/cpython/blob/91d71dd67074d4599b6bd49cc933f41f8bd57058/Python/ceval.c#L1198-L1225
If I find more, I'll add them

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

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

Python 3.16.0a0 (heads/main:e8158d1a02d, Aug 20 2026, 15:09:24) [Clang 21.0.0 (clang-2100.3.27.1)]

--with-dtrace を指定して Python をビルドし、probe.d と test.py の例を使って assertion を再現します。Python/import.c の import hook と、リンクされている箇所を含む Python/ceval.c の追加の DTrace コードを調査します。probe がアクティブな間に lone-surrogate の import が stale exception を残さず、debug assertion もトリガーしなくなれば完了です。