Avoid upcall arguments conversion for unicode decoder

Author: qunaibit

graalpython/com.oracle.graal.python.cext/src/unicodeobject.c

@@ -516,9 +516,15 @@ PyObject * PyUnicode_DecodeUTF8(const char *s, Py_ssize_t size, const char *erro
     return PyUnicode_DecodeUTF8Stateful(s, size, errors, NULL);
 }
 
-UPCALL_ID(PyUnicode_DecodeUTF8Stateful);
+typedef PyObject* (*unicode_DecodeUTF8Stateful_fun_t)(void *data, const char *errors, int consumed);
+UPCALL_TYPED_ID(PyUnicode_DecodeUTF8Stateful, unicode_DecodeUTF8Stateful_fun_t);
 PyObject * PyUnicode_DecodeUTF8Stateful(const char *s, Py_ssize_t size, const char *errors, Py_ssize_t *consumed) {
-	PyObject* result = UPCALL_CEXT_O(_jls_PyUnicode_DecodeUTF8Stateful, polyglot_from_i8_array(s, size), polyglot_from_string(errors, SRC_CS), consumed != NULL ? 1 : 0);
+	// This does deliberately not use UPCALL_CEXT_O to avoid argument conversion since
+	// 'PyUnicode_DecodeUTF8Stateful' really expects the bare pointer.
+	PyObject* result = _jls_PyUnicode_DecodeUTF8Stateful( 
+                                                polyglot_from_i8_array(s, size), 
+                                                polyglot_from_string(errors, SRC_CS), 
+                                                consumed != NULL ? 1 : 0);
 	if (result != NULL) {
 		if (consumed != NULL) {
 			*consumed = PyLong_AsSsize_t(PyTuple_GetItem(result, 1));
@@ -532,7 +538,10 @@ PyObject * PyUnicode_DecodeUTF8Stateful(const char *s, Py_ssize_t size, const ch
 // partially taken from CPython "Python/Objects/unicodeobject.c"
 PyObject * _PyUnicode_FromId(_Py_Identifier *id) {
     if (!id->object) {
-        id->object = PyUnicode_DecodeUTF8Stateful(id->string, strlen(id->string), NULL, NULL);
+        id->object = PyUnicode_DecodeUTF8Stateful(id->string, 
+                                                        strlen(id->string), 
+                                                        "strict", 
+                                                        NULL);
         if (!id->object) {
             return NULL;
         }

graalpython/com.oracle.graal.python.test/src/tests/cpyext/test_unicode.py

@@ -304,6 +304,24 @@ def compile_module(self, name):
         cmpfunc=unhandled_error_compare
     )
 
+    test_PyUnicode_DecodeUTF8Stateful = CPyExtFunction(
+        lambda args: args[0],
+        lambda: (
+            ("_type_", ),
+        ),
+        code="""PyObject* wrap_PyUnicode_DecodeUTF8Stateful(PyObject* _type_str) {
+            _Py_IDENTIFIER(_type_);
+            // _PyUnicode_FromId --> PyUnicode_DecodeUTF8Stateful
+            return _PyUnicode_FromId(&PyId__type_);
+        }
+        """,
+        resultspec="O",
+        argspec='O',
+        arguments=["PyObject* s"],
+        callfunction="wrap_PyUnicode_DecodeUTF8Stateful",
+        cmpfunc=unhandled_error_compare
+    )
+
     test_PyUnicode_AsLatin1String = CPyExtFunction(
         lambda args: args[0].encode("iso-8859-1"),
         lambda: (

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PythonCextBuiltins.java

@@ -1153,7 +1153,12 @@ protected static CharBuffer allocateCharBuffer(int cap) {
 
         @TruffleBoundary
         protected static String toString(CharBuffer cb) {
-            return cb.toString();
+            int len = cb.position();
+            if (len > 0) {
+                cb.rewind();
+                return cb.subSequence(0, len).toString();
+            }
+            return "";
         }
 
         @TruffleBoundary