Move observability-relevant structure fields to top

Some structures have fields that are used by out-of-process tools, like
Austin. Having these fields defined after some more complex structures
makes it hard to maintain these tools. With this change, we move the
declaration of the most useful fields to the top of the structure
definition. This reduces the amount of irrelevant information that the
mentioned tools have to replicate to retrieve the actually useful data

Author: P403n1x87

Include/internal/pycore_frame.h

@@ -49,16 +49,20 @@ enum _frameowner {
 typedef struct _PyInterpreterFrame {
     PyCodeObject *f_code; /* Strong reference */
     struct _PyInterpreterFrame *previous;
-    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 */
-    PyFrameObject *frame_obj; /* Strong reference, may be NULL. Only valid if not on C stack */
     // 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;
+
+    /* The fields above this line are declared as early as possible to
+       facilitate out-of-process observability tools. */
+
+    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 */
+    PyFrameObject *frame_obj; /* Strong reference, may be NULL. Only valid if not on C stack */
     int stacktop;  /* Offset of TOS from localsplus  */
     /* The return_offset determines where a `RETURN` should go in the caller,
      * relative to `prev_instr`.

Include/internal/pycore_interp.h

@@ -47,13 +47,35 @@ struct _Py_long_state {
    The PyInterpreterState typedef is in Include/pytypedefs.h.
    */
 struct _is {
-
-    struct _ceval_state ceval;
     PyInterpreterState *next;
 
+    int64_t id;
+    int64_t id_refcount;
+    int requires_idref;
+    PyThread_type_lock id_mutex;
+
+    /* Has been initialized to a safe state.
+
+       In order to be effective, this must be set to 0 during or right
+       after allocation. */
+    int _initialized;
+    int finalizing;
+
     uint64_t monitoring_version;
     uint64_t last_restart_version;
 
+    /* The fields above this line are declared as early as possible to
+       facilitate out-of-process observability tools. */
+
+    /* Set by Py_EndInterpreter().
+
+       Use _PyInterpreterState_GetFinalizing()
+       and _PyInterpreterState_SetFinalizing()
+       to access it, don't access it directly. */
+    _Py_atomic_address _finalizing;
+
+    PyCodeObject *interpreter_trampoline;
+
     struct pythreads {
         uint64_t next_unique_id;
         /* The linked list of threads, newest first. */
@@ -72,30 +94,22 @@ struct _is {
        Get runtime from tstate: tstate->interp->runtime. */
     struct pyruntimestate *runtime;
 
-    int64_t id;
-    int64_t id_refcount;
-    int requires_idref;
-    PyThread_type_lock id_mutex;
-
-    /* Has been initialized to a safe state.
-
-       In order to be effective, this must be set to 0 during or right
-       after allocation. */
-    int _initialized;
-    int finalizing;
-
-    /* Set by Py_EndInterpreter().
+    struct _gc_runtime_state gc;
 
-       Use _PyInterpreterState_GetFinalizing()
-       and _PyInterpreterState_SetFinalizing()
-       to access it, don't access it directly. */
-    _Py_atomic_address _finalizing;
+    /* The following fields are here to avoid allocation during init.
+       The data is exposed through PyInterpreterState pointer fields.
+       These fields should not be accessed directly outside of init.
 
-    struct _obmalloc_state obmalloc;
+       All other PyInterpreterState pointer fields are populated when
+       needed and default to NULL.
 
-    struct _gc_runtime_state gc;
+       For now there are some exceptions to that rule, which require
+       allocation during init.  These will be addressed on a case-by-case
+       basis.  Also see _PyRuntimeState regarding the various mutex fields.
+       */
 
-    struct _import_state imports;
+    /* The per-interpreter GIL, which might not be used. */
+    struct _gil_runtime_state _gil;
 
     // Dictionary of the sys module
     PyObject *sysdict;
@@ -133,6 +147,12 @@ struct _is {
     struct _warnings_runtime_state warnings;
     struct atexit_state atexit;
 
+    struct _ceval_state ceval;
+
+    struct _obmalloc_state obmalloc;
+
+    struct _import_state imports;
+
     PyObject *audit_hooks;
     PyType_WatchCallback type_watchers[TYPE_MAX_WATCHERS];
     PyCode_WatchCallback code_watchers[CODE_MAX_WATCHERS];
@@ -159,7 +179,6 @@ struct _is {
     struct ast_state ast;
     struct types_state types;
     struct callable_cache callable_cache;
-    PyCodeObject *interpreter_trampoline;
     _PyOptimizerObject *optimizer;
     uint16_t optimizer_resume_threshold;
     uint16_t optimizer_backedge_threshold;
@@ -176,21 +195,6 @@ struct _is {
     struct _Py_interp_cached_objects cached_objects;
     struct _Py_interp_static_objects static_objects;
 
-    /* The following fields are here to avoid allocation during init.
-       The data is exposed through PyInterpreterState pointer fields.
-       These fields should not be accessed directly outside of init.
-
-       All other PyInterpreterState pointer fields are populated when
-       needed and default to NULL.
-
-       For now there are some exceptions to that rule, which require
-       allocation during init.  These will be addressed on a case-by-case
-       basis.  Also see _PyRuntimeState regarding the various mutex fields.
-       */
-
-    /* The per-interpreter GIL, which might not be used. */
-    struct _gil_runtime_state _gil;
-
     /* the initial PyInterpreterState.threads.head */
     PyThreadState _initial_thread;
 };

Include/internal/pycore_runtime.h

@@ -84,13 +84,6 @@ typedef struct pyruntimestate {
        to access it, don't access it directly. */
     _Py_atomic_address _finalizing;
 
-    struct _pymem_allocators allocators;
-    struct _obmalloc_global_state obmalloc;
-    struct pyhash_runtime_state pyhash_state;
-    struct _time_runtime_state time;
-    struct _pythread_runtime_state threads;
-    struct _signals_runtime_state signals;
-
     struct pyinterpreters {
         PyThread_type_lock mutex;
         /* The linked list of interpreters, newest first. */
@@ -109,13 +102,24 @@ typedef struct pyruntimestate {
            using a Python int. */
         int64_t next_id;
     } interpreters;
+
+    unsigned long main_thread;
+
+    /* The fields above this line are declared as early as possible to
+       facilitate out-of-process observability tools. */
+
     // XXX Remove this field once we have a tp_* slot.
     struct _xidregistry {
         PyThread_type_lock mutex;
         struct _xidregitem *head;
     } xidregistry;
 
-    unsigned long main_thread;
+    struct _pymem_allocators allocators;
+    struct _obmalloc_global_state obmalloc;
+    struct pyhash_runtime_state pyhash_state;
+    struct _time_runtime_state time;
+    struct _pythread_runtime_state threads;
+    struct _signals_runtime_state signals;
 
     /* Used for the thread state bound to the current thread. */
     Py_tss_t autoTSSkey;