GH-96421: Insert shim frame on entry to interpreter

Include/internal/pycore_code.h

@@ -456,6 +456,16 @@ _PyCode_LineNumberFromArray(PyCodeObject *co, int index)
     }
 }
 
+typedef struct _PyShimCodeDef {
+    const uint8_t *code;
+    int codelen;
+    int stacksize;
+    const char *cname;
+} _PyShimCodeDef;
+
+extern PyCodeObject *
+_Py_MakeShimCode(const _PyShimCodeDef *code);
+
 
 #ifdef __cplusplus
 }

Include/internal/pycore_frame.h

@@ -42,27 +42,27 @@ 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
     // frame. Rather, it is the code unit *prior to* the *next* instruction. For
     // 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;
 }

Include/internal/pycore_global_strings.h

@@ -48,6 +48,7 @@ struct _Py_global_strings {
         STRUCT_FOR_STR(newline, "\n")
         STRUCT_FOR_STR(open_br, "{")
         STRUCT_FOR_STR(percent, "%")
+        STRUCT_FOR_STR(shim_name, "<shim>")
         STRUCT_FOR_STR(utf_8, "utf-8")
     } literals;
 

Include/internal/pycore_interp.h

@@ -186,6 +186,7 @@ struct _is {
     struct ast_state ast;
     struct types_state types;
     struct callable_cache callable_cache;
+    PyCodeObject *interpreter_trampoline;
 
     /* The following fields are here to avoid allocation during init.
        The data is exposed through PyInterpreterState pointer fields.