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.

1 files changed, 8 insertions, 9 deletions

diff --git a/Include/internal/pycore_frame.h b/Include/internal/pycore_frame.h
index feee692d0f..7fa410d288 100644
--- a/Include/internal/pycore_frame.h
+++ b/Include/internal/pycore_frame.h
@@ -42,17 +42,18 @@ typedef enum _framestate {
 enum _frameowner {
     FRAME_OWNED_BY_THREAD = 0,
     FRAME_OWNED_BY_GENERATOR = 1,
-    FRAME_OWNED_BY_FRAME_OBJECT = 2
+    FRAME_OWNED_BY_FRAME_OBJECT = 2,
+    FRAME_OWNED_BY_CSTACK = 3,
 };
 
 typedef struct _PyInterpreterFrame {
     /* "Specials" section */
-    PyObject *f_funcobj; /* Strong reference */
-    PyObject *f_globals; /* Borrowed reference */
-    PyObject *f_builtins; /* Borrowed reference */
-    PyObject *f_locals; /* Strong reference, may be NULL */
+    PyObject *f_funcobj; /* Strong reference. Only valid if not on C stack */
+    PyObject *f_globals; /* Borrowed reference. Only valid if not on C stack */
+    PyObject *f_builtins; /* Borrowed reference. Only valid if not on C stack */
+    PyObject *f_locals; /* Strong reference, may be NULL. Only valid if not on C stack */
     PyCodeObject *f_code; /* Strong reference */
-    PyFrameObject *frame_obj; /* Strong reference, may be NULL */
+    PyFrameObject *frame_obj; /* Strong reference, may be NULL. Only valid if not on C stack */
     /* Linkage section */
     struct _PyInterpreterFrame *previous;
     // NOTE: This is not necessarily the last instruction started in the given
@@ -60,9 +61,8 @@ typedef struct _PyInterpreterFrame {
     // example, it may be an inline CACHE entry, an instruction we just jumped
     // over, or (in the case of a newly-created frame) a totally invalid value:
     _Py_CODEUNIT *prev_instr;
-    int stacktop;     /* Offset of TOS from localsplus  */
+    int stacktop;  /* Offset of TOS from localsplus  */
     uint16_t yield_offset;
-    bool is_entry;  // Whether this is the "root" frame for the current _PyCFrame.
     char owner;
     /* Locals and stack */
     PyObject *localsplus[1];
@@ -110,7 +110,6 @@ _PyFrame_InitializeSpecials(
     frame->stacktop = code->co_nlocalsplus;
     frame->frame_obj = NULL;
     frame->prev_instr = _PyCode_CODE(code) - 1;
-    frame->is_entry = false;
     frame->yield_offset = 0;
     frame->owner = FRAME_OWNED_BY_THREAD;
 }