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

[stestagg]

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:

cpython/Python/import.c

Lines 4106 to 4107 in e8158d1

	if (PyDTrace_IMPORT_FIND_LOAD_START_ENABLED())
	PyDTrace_IMPORT_FIND_LOAD_START(PyUnicode_AsUTF8(abs_name));

Caution

EDIT: I found some more cases of drace code doing the same, This isn't just limited to import machinery:

cpython/Python/ceval.c

Lines 1198 to 1225 in 91d71dd

	dtrace_function_entry(_PyInterpreterFrame *frame)
	{
	const char *filename;
	const char *funcname;
	int lineno;
	PyCodeObject *code = _PyFrame_GetCode(frame);
	filename = PyUnicode_AsUTF8(code->co_filename);
	funcname = PyUnicode_AsUTF8(code->co_name);
	lineno = PyUnstable_InterpreterFrame_GetLine(frame);
	PyDTrace_FUNCTION_ENTRY(filename, funcname, lineno);
	}
	static void
	dtrace_function_return(_PyInterpreterFrame *frame)
	{
	const char *filename;
	const char *funcname;
	int lineno;
	PyCodeObject *code = _PyFrame_GetCode(frame);
	filename = PyUnicode_AsUTF8(code->co_filename);
	funcname = PyUnicode_AsUTF8(code->co_name);
	lineno = PyUnstable_InterpreterFrame_GetLine(frame);
	PyDTrace_FUNCTION_RETURN(filename, funcname, lineno);
	}

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)]