GH-96421: Insert shim frame on entry to interpreter (GH-96319)

* Adds EXIT_INTERPRETER instruction to exit PyEval_EvalDefault()

* Simplifies RETURN_VALUE, YIELD_VALUE and RETURN_GENERATOR instructions as they no longer need to check for entry frames.

Objects/codeobject.c

@@ -2264,3 +2264,78 @@ _PyStaticCode_Init(PyCodeObject *co)
     _PyCode_Quicken(co);
     return 0;
 }
+
+#define MAX_CODE_UNITS_PER_LOC_ENTRY 8
+
+PyCodeObject *
+_Py_MakeShimCode(const _PyShimCodeDef *codedef)
+{
+    PyObject *name = NULL;
+    PyObject *co_code = NULL;
+    PyObject *lines = NULL;
+    PyCodeObject *codeobj = NULL;
+    uint8_t *loc_table = NULL;
+
+    name = _PyUnicode_FromASCII(codedef->cname, strlen(codedef->cname));
+    if (name == NULL) {
+        goto cleanup;
+    }
+    co_code = PyBytes_FromStringAndSize(
+        (const char *)codedef->code, codedef->codelen);
+    if (co_code == NULL) {
+        goto cleanup;
+    }
+    int code_units = codedef->codelen / sizeof(_Py_CODEUNIT);
+    int loc_entries = (code_units + MAX_CODE_UNITS_PER_LOC_ENTRY - 1) /
+                      MAX_CODE_UNITS_PER_LOC_ENTRY;
+    loc_table = PyMem_Malloc(loc_entries);
+    if (loc_table == NULL) {
+        PyErr_NoMemory();
+        goto cleanup;
+    }
+    for (int i = 0; i < loc_entries-1; i++) {
+         loc_table[i] = 0x80 | (PY_CODE_LOCATION_INFO_NONE << 3) | 7;
+         code_units -= MAX_CODE_UNITS_PER_LOC_ENTRY;
+    }
+    assert(loc_entries > 0);
+    assert(code_units > 0 && code_units <= MAX_CODE_UNITS_PER_LOC_ENTRY);
+    loc_table[loc_entries-1] = 0x80 |
+        (PY_CODE_LOCATION_INFO_NONE << 3) | (code_units-1);
+    lines = PyBytes_FromStringAndSize((const char *)loc_table, loc_entries);
+    PyMem_Free(loc_table);
+    if (lines == NULL) {
+        goto cleanup;
+    }
+    _Py_DECLARE_STR(shim_name, "<shim>");
+    struct _PyCodeConstructor con = {
+        .filename = &_Py_STR(shim_name),
+        .name = name,
+        .qualname = name,
+        .flags = CO_NEWLOCALS | CO_OPTIMIZED,
+
+        .code = co_code,
+        .firstlineno = 1,
+        .linetable = lines,
+
+        .consts = (PyObject *)&_Py_SINGLETON(tuple_empty),
+        .names = (PyObject *)&_Py_SINGLETON(tuple_empty),
+
+        .localsplusnames = (PyObject *)&_Py_SINGLETON(tuple_empty),
+        .localspluskinds = (PyObject *)&_Py_SINGLETON(bytes_empty),
+
+        .argcount = 0,
+        .posonlyargcount = 0,
+        .kwonlyargcount = 0,
+
+        .stacksize = codedef->stacksize,
+
+        .exceptiontable = (PyObject *)&_Py_SINGLETON(bytes_empty),
+    };
+
+    codeobj = _PyCode_New(&con);
+cleanup:
+    Py_XDECREF(name);
+    Py_XDECREF(co_code);
+    Py_XDECREF(lines);
+    return codeobj;
+}