gh-106597: Add debugging struct with offsets for out-of-process tools (#106598)

Include/internal/pycore_runtime.h

@@ -53,12 +53,101 @@ typedef struct _Py_AuditHookEntry {
     void *userData;
 } _Py_AuditHookEntry;
 
+typedef struct _Py_DebugOffsets {
+    char cookie[8];
+    uint64_t version;
+    // Runtime state offset;
+    struct _runtime_state {
+        off_t finalizing;
+        off_t interpreters_head;
+    } runtime_state;
+
+    // Interpreter state offset;
+    struct _interpreter_state {
+        off_t next;
+        off_t threads_head;
+        off_t gc;
+        off_t imports_modules;
+        off_t sysdict;
+        off_t builtins;
+        off_t ceval_gil;
+        off_t gil_runtime_state_locked;
+        off_t gil_runtime_state_holder;
+    } interpreter_state;
+
+    // Thread state offset;
+    struct _thread_state{
+        off_t prev;
+        off_t next;
+        off_t interp;
+        off_t cframe;
+        off_t thread_id;
+        off_t native_thread_id;
+    } thread_state;
+
+    // InterpreterFrame offset;
+    struct _interpreter_frame {
+        off_t previous;
+        off_t executable;
+        off_t prev_instr;
+        off_t localsplus;
+        off_t owner;
+    } interpreter_frame;
+
+    // CFrame offset;
+    struct _cframe {
+        off_t current_frame;
+        off_t previous;
+    } cframe;
+
+    // Code object offset;
+    struct _code_object {
+        off_t filename;
+        off_t name;
+        off_t linetable;
+        off_t firstlineno;
+        off_t argcount;
+        off_t localsplusnames;
+        off_t localspluskinds;
+        off_t co_code_adaptive;
+    } code_object;
+
+    // PyObject offset;
+    struct _pyobject {
+        off_t ob_type;
+    } pyobject;
+
+    // PyTypeObject object offset;
+    struct _type_object {
+        off_t tp_name;
+    } type_object;
+
+    // PyTuple object offset;
+    struct _tuple_object {
+        off_t ob_item;
+    } tuple_object;
+} _Py_DebugOffsets;
+
 /* Full Python runtime state */
 
 /* _PyRuntimeState holds the global state for the CPython runtime.
    That data is exposed in the internal API as a static variable (_PyRuntime).
    */
 typedef struct pyruntimestate {
+    /* This field must be first to facilitate locating it by out of process
+     * debuggers. Out of process debuggers will use the offsets contained in this
+     * field to be able to locate other fields in several interpreter structures
+     * in a way that doesn't require them to know the exact layout of those
+     * structures.
+     *
+     * IMPORTANT:
+     * This struct is **NOT** backwards compatible between minor version of the
+     * interpreter and the members, order of members and size can change between
+     * minor versions. This struct is only guaranteed to be stable between patch
+     * versions for a given minor version of the interpreter.
+     */
+    _Py_DebugOffsets debug_offsets;
+
     /* Has been initialized to a safe state.
 
        In order to be effective, this must be set to 0 during or right