Allow gap before first non-Lisp pseudovec member

Problem reported by Keith David Bershatsky in:
https://lists.gnu.org/r/emacs-devel/2019-04/msg00259.html
Solution suggested by Stefan Monnier in:
https://lists.gnu.org/r/emacs-devel/2019-04/msg00282.html
* src/buffer.h (BUFFER_LISP_SIZE): Simplify by using PSEUDOVECSIZE.
(BUFFER_REST_SIZE): Simplify by using VECSIZE and BUFFER_LISP_SIZE.
* src/lisp.h (PSEUDOVECSIZE): Base it on the last Lisp field,
not the first non-Lisp field.  All callers changed.  Callers
without Lisp fields changed to use ALLOCATE_PLAIN_PSEUDOVECTOR.
(ALLOCATE_PLAIN_PSEUDOVECTOR): New macro.

22 files changed, 76 insertions, 78 deletions

diff --git a/src/alloc.c b/src/alloc.c
index e48807c49ad..dd783863be8 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -3718,8 +3718,8 @@ Its value is void, and its function definition and property list are nil.  */)
 Lisp_Object
 make_misc_ptr (void *a)
 {
-  struct Lisp_Misc_Ptr *p = ALLOCATE_PSEUDOVECTOR (struct Lisp_Misc_Ptr, pointer,
-                                                   PVEC_MISC_PTR);
+  struct Lisp_Misc_Ptr *p = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_Misc_Ptr,
+                                                         PVEC_MISC_PTR);
   p->pointer = a;
   return make_lisp_ptr (p, Lisp_Vectorlike);
 }
@@ -3729,7 +3729,7 @@ make_misc_ptr (void *a)
 Lisp_Object
 build_overlay (Lisp_Object start, Lisp_Object end, Lisp_Object plist)
 {
-  struct Lisp_Overlay *p = ALLOCATE_PSEUDOVECTOR (struct Lisp_Overlay, next,
+  struct Lisp_Overlay *p = ALLOCATE_PSEUDOVECTOR (struct Lisp_Overlay, plist,
                                                   PVEC_OVERLAY);
   Lisp_Object overlay = make_lisp_ptr (p, Lisp_Vectorlike);
   OVERLAY_START (overlay) = start;
@@ -3743,8 +3743,8 @@ DEFUN ("make-marker", Fmake_marker, Smake_marker, 0, 0, 0,
        doc: /* Return a newly allocated marker which does not point at any place.  */)
   (void)
 {
-  struct Lisp_Marker *p = ALLOCATE_PSEUDOVECTOR (struct Lisp_Marker, buffer,
-                                                 PVEC_MARKER);
+  struct Lisp_Marker *p = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_Marker,
+                                                       PVEC_MARKER);
   p->buffer = 0;
   p->bytepos = 0;
   p->charpos = 0;
@@ -3766,8 +3766,8 @@ build_marker (struct buffer *buf, ptrdiff_t charpos, ptrdiff_t bytepos)
   /* Every character is at least one byte.  */
   eassert (charpos <= bytepos);
 
-  struct Lisp_Marker *m = ALLOCATE_PSEUDOVECTOR (struct Lisp_Marker, buffer,
-                                                 PVEC_MARKER);
+  struct Lisp_Marker *m = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_Marker,
+                                                       PVEC_MARKER);
   m->buffer = buf;
   m->charpos = charpos;
   m->bytepos = bytepos;
@@ -3821,8 +3821,8 @@ make_event_array (ptrdiff_t nargs, Lisp_Object *args)
 Lisp_Object
 make_user_ptr (void (*finalizer) (void *), void *p)
 {
-  struct Lisp_User_Ptr *uptr = ALLOCATE_PSEUDOVECTOR (struct Lisp_User_Ptr,
-                                                      finalizer, PVEC_USER_PTR);
+  struct Lisp_User_Ptr *uptr
+    = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_User_Ptr, PVEC_USER_PTR);
   uptr->finalizer = finalizer;
   uptr->p = p;
   return make_lisp_ptr (uptr, Lisp_Vectorlike);
@@ -3945,7 +3945,7 @@ FUNCTION.  FUNCTION will be run once per finalizer object.  */)
   (Lisp_Object function)
 {
   struct Lisp_Finalizer *finalizer
-    = ALLOCATE_PSEUDOVECTOR (struct Lisp_Finalizer, prev, PVEC_FINALIZER);
+    = ALLOCATE_PSEUDOVECTOR (struct Lisp_Finalizer, function, PVEC_FINALIZER);
   finalizer->function = function;
   finalizer->prev = finalizer->next = NULL;
   finalizer_insert (&finalizers, finalizer);
diff --git a/src/bignum.c b/src/bignum.c
index 4118601e108..009d73118c2 100644
--- a/src/bignum.c
+++ b/src/bignum.c
@@ -86,8 +86,8 @@ make_bignum_bits (size_t bits)
   if (integer_width < bits)
     overflow_error ();
 
-  struct Lisp_Bignum *b = ALLOCATE_PSEUDOVECTOR (struct Lisp_Bignum, value,
-                                                 PVEC_BIGNUM);
+  struct Lisp_Bignum *b = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_Bignum,
+                                                       PVEC_BIGNUM);
   mpz_init (b->value);
   mpz_swap (b->value, mpz[0]);
   return make_lisp_ptr (b, Lisp_Vectorlike);
@@ -342,8 +342,8 @@ bignum_to_string (Lisp_Object num, int base)
 Lisp_Object
 make_bignum_str (char const *num, int base)
 {
-  struct Lisp_Bignum *b = ALLOCATE_PSEUDOVECTOR (struct Lisp_Bignum, value,
-                                                 PVEC_BIGNUM);
+  struct Lisp_Bignum *b = ALLOCATE_PLAIN_PSEUDOVECTOR (struct Lisp_Bignum,
+                                                       PVEC_BIGNUM);
   mpz_init (b->value);
   int check = mpz_set_str (b->value, num, base);
   eassert (check == 0);
diff --git a/src/buffer.h b/src/buffer.h
index 63b162161c6..f42c3e97b97 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -741,8 +741,8 @@ struct buffer
      See `cursor-type' for other values.  */
   Lisp_Object cursor_in_non_selected_windows_;
 
-  /* No more Lisp_Object beyond this point.  Except undo_list,
-     which is handled specially in Fgarbage_collect.  */
+  /* No more Lisp_Object beyond cursor_in_non_selected_windows_.
+     Except undo_list, which is handled specially in Fgarbage_collect.  */
 
   /* This structure holds the coordinates of the buffer contents
      in ordinary buffers.  In indirect buffers, this is not used.  */
@@ -1019,14 +1019,12 @@ bset_width_table (struct buffer *b, Lisp_Object val)
    structure, make sure that this is still correct.  */
 
 #define BUFFER_LISP_SIZE                                                \
-  ((offsetof (struct buffer, own_text) - header_size) / word_size)
+  PSEUDOVECSIZE (struct buffer, cursor_in_non_selected_windows_)
 
-/* Size of the struct buffer part beyond leading Lisp_Objects, in word_size
-   units.  Rounding is needed for --with-wide-int configuration.  */
+/* Allocated size of the struct buffer part beyond leading
+   Lisp_Objects, in word_size units.  */
 
-#define BUFFER_REST_SIZE                                                \
-  ((((sizeof (struct buffer) - offsetof (struct buffer, own_text))      \
-     + (word_size - 1)) & ~(word_size - 1)) / word_size)
+#define BUFFER_REST_SIZE (VECSIZE (struct buffer) - BUFFER_LISP_SIZE)
 
 /* Initialize the pseudovector header of buffer object.  BUFFER_LISP_SIZE
    is required for GC, but BUFFER_REST_SIZE is set up just to be consistent
diff --git a/src/emacs-module.c b/src/emacs-module.c
index 2bb1062574e..47ca3368c0f 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -427,7 +427,7 @@ static struct Lisp_Module_Function *
 allocate_module_function (void)
 {
   return ALLOCATE_PSEUDOVECTOR (struct Lisp_Module_Function,
-                                min_arity, PVEC_MODULE_FUNCTION);
+                                documentation, PVEC_MODULE_FUNCTION);
 }
 
 #define XSET_MODULE_FUNCTION(var, ptr) \
diff --git a/src/fns.c b/src/fns.c
index b97b132b0fe..c3202495daf 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -3904,7 +3904,7 @@ static struct Lisp_Hash_Table *
 allocate_hash_table (void)
 {
   return ALLOCATE_PSEUDOVECTOR (struct Lisp_Hash_Table,
-                                count, PVEC_HASH_TABLE);
+                                index, PVEC_HASH_TABLE);
 }
 
 /* An upper bound on the size of a hash table index.  It must fit in
diff --git a/src/frame.c b/src/frame.c
index 6fdb7d0cbb9..192ef4244fb 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -798,7 +798,8 @@ adjust_frame_size (struct frame *f, int new_width, int new_height, int inhibit,
 static struct frame *
 allocate_frame (void)
 {
-  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct frame, face_cache, PVEC_FRAME);
+  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct frame, tool_bar_items,
+                                       PVEC_FRAME);
 }
 
 struct frame *
diff --git a/src/frame.h b/src/frame.h
index ed62e7ace0f..ec8f61465f2 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -190,9 +190,6 @@ struct frame
   Lisp_Object current_tool_bar_string;
 #endif
 
-  /* Desired and current tool-bar items.  */
-  Lisp_Object tool_bar_items;
-
 #ifdef USE_GTK
   /* Where tool bar is, can be left, right, top or bottom.
      Except with GTK, the only supported position is `top'.  */
@@ -204,7 +201,9 @@ struct frame
   Lisp_Object font_data;
 #endif
 
-  /* Beyond here, there should be no more Lisp_Object components.  */
+  /* Desired and current tool-bar items.  */
+  Lisp_Object tool_bar_items;
+  /* tool_bar_items should be the last Lisp_Object member.  */
 
   /* Cache of realized faces.  */
   struct face_cache *face_cache;
diff --git a/src/lisp.h b/src/lisp.h
index a0a7cbdf518..681efc3b52b 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1904,9 +1904,9 @@ memclear (void *p, ptrdiff_t nbytes)
    at the end and we need to compute the number of Lisp_Object fields (the
    ones that the GC needs to trace).  */
 
-#define PSEUDOVECSIZE(type, nonlispfield)                       \
-   (offsetof (type, nonlispfield) < header_size                 \
-    ? 0 : (offsetof (type, nonlispfield) - header_size) / word_size)
+#define PSEUDOVECSIZE(type, lastlispfield)                              \
+  (offsetof (type, lastlispfield) + word_size < header_size             \
+   ? 0 : (offsetof (type, lastlispfield) + word_size - header_size) / word_size)
 
 /* Compute A OP B, using the unsigned comparison operator OP.  A and B
    should be integer expressions.  This is not the same as
@@ -2109,11 +2109,14 @@ enum char_table_specials
     /* This is the number of slots that every char table must have.  This
        counts the ordinary slots and the top, defalt, parent, and purpose
        slots.  */
-    CHAR_TABLE_STANDARD_SLOTS = PSEUDOVECSIZE (struct Lisp_Char_Table, extras),
+    CHAR_TABLE_STANDARD_SLOTS
+      = (PSEUDOVECSIZE (struct Lisp_Char_Table, contents) - 1
+         + (1 << CHARTAB_SIZE_BITS_0)),
 
-    /* This is an index of first Lisp_Object field in Lisp_Sub_Char_Table
+    /* This is the index of the first Lisp_Object field in Lisp_Sub_Char_Table
        when the latter is treated as an ordinary Lisp_Vector.  */
-    SUB_CHAR_TABLE_OFFSET = PSEUDOVECSIZE (struct Lisp_Sub_Char_Table, contents)
+    SUB_CHAR_TABLE_OFFSET
+      = PSEUDOVECSIZE (struct Lisp_Sub_Char_Table, contents) - 1
   };
 
 /* Sanity-check pseudovector layout.  */
@@ -2313,8 +2316,8 @@ struct Lisp_Hash_Table
      hash table size to reduce collisions.  */
   Lisp_Object index;
 
-  /* Only the fields above are traced normally by the GC.  The ones below
-     `count' are special and are either ignored by the GC or traced in
+  /* Only the fields above are traced normally by the GC.  The ones after
+     'index' are special and are either ignored by the GC or traced in
      a special way (e.g. because of weakness).  */
 
   /* Number of key/value entries in the table.  */
@@ -3940,6 +3943,11 @@ make_nil_vector (ptrdiff_t size)
 extern struct Lisp_Vector *allocate_pseudovector (int, int, int,
                                                   enum pvec_type);
 
+/* Allocate uninitialized pseudovector with no Lisp_Object slots.  */
+
+#define ALLOCATE_PLAIN_PSEUDOVECTOR(type, tag) \
+  ((type *) allocate_pseudovector (VECSIZE (type), 0, 0, tag))
+
 /* Allocate partially initialized pseudovector where all Lisp_Object
    slots are set to Qnil but the rest (if any) is left uninitialized.  */
 
diff --git a/src/pdumper.c b/src/pdumper.c
index b19f206d1bd..cb2915cb203 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -2702,7 +2702,7 @@ dump_hash_table (struct dump_context *ctx,
                  Lisp_Object object,
                  dump_off offset)
 {
-#if CHECK_STRUCTS && !defined (HASH_Lisp_Hash_Table_73C9BFB7D1)
+#if CHECK_STRUCTS && !defined HASH_Lisp_Hash_Table_EF95ED06FF
 # error "Lisp_Hash_Table changed. See CHECK_STRUCTS comment."
 #endif
   const struct Lisp_Hash_Table *hash_in = XHASH_TABLE (object);
@@ -2770,7 +2770,7 @@ dump_hash_table (struct dump_context *ctx,
 static dump_off
 dump_buffer (struct dump_context *ctx, const struct buffer *in_buffer)
 {
-#if CHECK_STRUCTS && !defined HASH_buffer_2CEE653E74
+#if CHECK_STRUCTS && !defined HASH_buffer_E34A11C6B9
 # error "buffer changed. See CHECK_STRUCTS comment."
 #endif
   struct buffer munged_buffer = *in_buffer;
diff --git a/src/process.c b/src/process.c
index 802ac026249..6770a5ed884 100644
--- a/src/process.c
+++ b/src/process.c
@@ -858,7 +858,8 @@ allocate_pty (char pty_name[PTY_NAME_SIZE])
 static struct Lisp_Process *
 allocate_process (void)
 {
-  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct Lisp_Process, pid, PVEC_PROCESS);
+  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct Lisp_Process, thread,
+                                       PVEC_PROCESS);
 }
 
 static Lisp_Object
diff --git a/src/process.h b/src/process.h
index d66aa062a54..5e957c4298e 100644
--- a/src/process.h
+++ b/src/process.h
@@ -117,9 +117,7 @@ struct Lisp_Process
 
     /* The thread a process is linked to, or nil for any thread.  */
     Lisp_Object thread;
-
-    /* After this point, there are no Lisp_Objects any more.  */
-    /* alloc.c assumes that `pid' is the first such non-Lisp slot.  */
+    /* After this point, there are no Lisp_Objects.  */
 
     /* Process ID.  A positive value is a child process ID.
        Zero is for pseudo-processes such as network or serial connections,
diff --git a/src/termhooks.h b/src/termhooks.h
index ca6782f461b..a92b981110d 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -408,7 +408,7 @@ struct terminal
      whether the mapping is available.  */
   Lisp_Object glyph_code_table;
 
-  /* All fields before `next_terminal' should be Lisp_Object and are traced
+  /* All earlier fields should be Lisp_Objects and are traced
      by the GC.  All fields afterwards are ignored by the GC.  */
 
   /* Chain of all terminal devices. */
diff --git a/src/terminal.c b/src/terminal.c
index 1d7a965dd26..0ee0121e35e 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -264,8 +264,8 @@ get_named_terminal (const char *name)
 static struct terminal *
 allocate_terminal (void)
 {
-  return ALLOCATE_ZEROED_PSEUDOVECTOR
-    (struct terminal, next_terminal, PVEC_TERMINAL);
+  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct terminal, glyph_code_table,
+                                       PVEC_TERMINAL);
 }
 
 /* Create a new terminal object of TYPE and add it to the terminal list.  RIF
diff --git a/src/thread.c b/src/thread.c
index e51d6144347..670680f2b0d 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -267,7 +267,7 @@ informational only.  */)
   if (!NILP (name))
     CHECK_STRING (name);
 
-  mutex = ALLOCATE_PSEUDOVECTOR (struct Lisp_Mutex, mutex, PVEC_MUTEX);
+  mutex = ALLOCATE_PSEUDOVECTOR (struct Lisp_Mutex, name, PVEC_MUTEX);
   memset ((char *) mutex + offsetof (struct Lisp_Mutex, mutex),
           0, sizeof (struct Lisp_Mutex) - offsetof (struct Lisp_Mutex,
                                                     mutex));
@@ -386,7 +386,7 @@ informational only.  */)
   if (!NILP (name))
     CHECK_STRING (name);
 
-  condvar = ALLOCATE_PSEUDOVECTOR (struct Lisp_CondVar, cond, PVEC_CONDVAR);
+  condvar = ALLOCATE_PSEUDOVECTOR (struct Lisp_CondVar, name, PVEC_CONDVAR);
   memset ((char *) condvar + offsetof (struct Lisp_CondVar, cond),
           0, sizeof (struct Lisp_CondVar) - offsetof (struct Lisp_CondVar,
                                                       cond));
@@ -805,7 +805,7 @@ If NAME is given, it must be a string; it names the new thread.  */)
   if (!NILP (name))
     CHECK_STRING (name);
 
-  new_thread = ALLOCATE_PSEUDOVECTOR (struct thread_state, m_stack_bottom,
+  new_thread = ALLOCATE_PSEUDOVECTOR (struct thread_state, event_object,
                                       PVEC_THREAD);
   memset ((char *) new_thread + offset, 0,
           sizeof (struct thread_state) - offset);
@@ -1064,7 +1064,7 @@ static void
 init_main_thread (void)
 {
   main_thread.s.header.size
-    = PSEUDOVECSIZE (struct thread_state, m_stack_bottom);
+    = PSEUDOVECSIZE (struct thread_state, event_object);
   XSETPVECTYPE (&main_thread.s, PVEC_THREAD);
   main_thread.s.m_last_thing_searched = Qnil;
   main_thread.s.m_saved_last_thing_searched = Qnil;
diff --git a/src/thread.h b/src/thread.h
index 50f8f5cbe0a..0514669a87d 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -61,8 +61,8 @@ struct thread_state
   /* If we are waiting for some event, this holds the object we are
      waiting on.  */
   Lisp_Object event_object;
+  /* event_object must be the last Lisp field.  */
 
-  /* m_stack_bottom must be the first non-Lisp field.  */
   /* An address near the bottom of the stack.
      Tells GC how to save a copy of the stack.  */
   char const *m_stack_bottom;
diff --git a/src/w32term.c b/src/w32term.c
index 7dbeda7a716..bb1f0bad018 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -3896,7 +3896,7 @@ x_scroll_bar_create (struct window *w, int left, int top, int width, int height,
   HWND hwnd;
   SCROLLINFO si;
   struct scroll_bar *bar
-    = ALLOCATE_PSEUDOVECTOR (struct scroll_bar, top, PVEC_OTHER);
+    = ALLOCATE_PSEUDOVECTOR (struct scroll_bar, w32_widget_high, PVEC_OTHER);
   Lisp_Object barobj;
 
   block_input ();
diff --git a/src/window.c b/src/window.c
index be338c2af61..f911c0c7d44 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4170,8 +4170,8 @@ temp_output_buffer_show (register Lisp_Object buf)
 static struct window *
 allocate_window (void)
 {
-  return ALLOCATE_ZEROED_PSEUDOVECTOR
-    (struct window, current_matrix, PVEC_WINDOW);
+  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct window, mode_line_help_echo,
+                                       PVEC_WINDOW);
 }
 
 /* Make new window, have it replace WINDOW in window-tree, and make
@@ -6710,7 +6710,8 @@ struct save_window_data
     Lisp_Object saved_windows;
 
     /* All fields above are traced by the GC.
-       From `frame-cols' down, the fields are ignored by the GC.  */
+       After saved_windows, the fields are ignored by the GC.  */
+
     /* We should be able to do without the following two.  */
     int frame_cols, frame_lines;
     /* These two should get eventually replaced by their pixel
@@ -7383,15 +7384,11 @@ redirection (see `redirect-frame-focus').  The variable
 saved by this function.  */)
   (Lisp_Object frame)
 {
-  Lisp_Object tem;
-  ptrdiff_t i, n_windows;
-  struct save_window_data *data;
   struct frame *f = decode_live_frame (frame);
-
-  n_windows = count_windows (XWINDOW (FRAME_ROOT_WINDOW (f)));
-  data = ALLOCATE_PSEUDOVECTOR (struct save_window_data, frame_cols,
-                               PVEC_WINDOW_CONFIGURATION);
-
+  ptrdiff_t n_windows = count_windows (XWINDOW (FRAME_ROOT_WINDOW (f)));
+  struct save_window_data *data
+    = ALLOCATE_PSEUDOVECTOR (struct save_window_data, saved_windows,
+                             PVEC_WINDOW_CONFIGURATION);
   data->frame_cols = FRAME_COLS (f);
   data->frame_lines = FRAME_LINES (f);
   data->frame_menu_bar_lines = FRAME_MENU_BAR_LINES (f);
@@ -7407,9 +7404,9 @@ saved by this function.  */)
   data->minibuf_selected_window = minibuf_level > 0 ? minibuf_selected_window : Qnil;
   data->root_window = FRAME_ROOT_WINDOW (f);
   data->focus_frame = FRAME_FOCUS_FRAME (f);
-  tem = make_uninit_vector (n_windows);
+  Lisp_Object tem = make_uninit_vector (n_windows);
   data->saved_windows = tem;
-  for (i = 0; i < n_windows; i++)
+  for (ptrdiff_t i = 0; i < n_windows; i++)
     ASET (tem, i, make_nil_vector (VECSIZE (struct saved_window)));
   save_window_save (FRAME_ROOT_WINDOW (f), XVECTOR (tem), 0);
   XSETWINDOW_CONFIGURATION (tem, data);
diff --git a/src/window.h b/src/window.h
index 4235a6eade2..fdef407041b 100644
--- a/src/window.h
+++ b/src/window.h
@@ -212,9 +212,8 @@ struct window
     /* The help echo text for this window.  Qnil if there's none.  */
     Lisp_Object mode_line_help_echo;
 
-    /* No Lisp data may follow below this point without changing
-       mark_object in alloc.c.  The member current_matrix must be the
-       first non-Lisp member.  */
+    /* No Lisp data may follow this point; mode_line_help_echo must be
+       the last Lisp member.  */
 
     /* Glyph matrices.  */
     struct glyph_matrix *current_matrix;
diff --git a/src/xterm.c b/src/xterm.c
index 2f830afe61b..5aa3e3ff25c 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -6611,8 +6611,8 @@ x_scroll_bar_create (struct window *w, int top, int left,
                      int width, int height, bool horizontal)
 {
   struct frame *f = XFRAME (w->frame);
-  struct scroll_bar *bar
-    = ALLOCATE_PSEUDOVECTOR (struct scroll_bar, x_window, PVEC_OTHER);
+  struct scroll_bar *bar = ALLOCATE_PSEUDOVECTOR (struct scroll_bar, prev,
+                                                  PVEC_OTHER);
   Lisp_Object barobj;
 
   block_input ();
diff --git a/src/xterm.h b/src/xterm.h
index 972a10f4d41..c5ad38650c2 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -897,7 +897,7 @@ struct scroll_bar
   /* The next and previous in the chain of scroll bars in this frame.  */
   Lisp_Object next, prev;
 
-  /* Fields from `x_window' down will not be traced by the GC.  */
+  /* Fields after 'prev' are not traced by the GC.  */
 
   /* The X window representing this scroll bar.  */
   Window x_window;
diff --git a/src/xwidget.c b/src/xwidget.c
index c56284928e3..2486a2d4da8 100644
--- a/src/xwidget.c
+++ b/src/xwidget.c
@@ -41,14 +41,13 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 static struct xwidget *
 allocate_xwidget (void)
 {
-  return ALLOCATE_PSEUDOVECTOR (struct xwidget, height, PVEC_XWIDGET);
+  return ALLOCATE_PSEUDOVECTOR (struct xwidget, script_callbacks, PVEC_XWIDGET);
 }
 
 static struct xwidget_view *
 allocate_xwidget_view (void)
 {
-  return ALLOCATE_PSEUDOVECTOR (struct xwidget_view, redisplayed,
-                                PVEC_XWIDGET_VIEW);
+  return ALLOCATE_PSEUDOVECTOR (struct xwidget_view, w, PVEC_XWIDGET_VIEW);
 }
 
 #define XSETXWIDGET(a, b) XSETPSEUDOVECTOR (a, b, PVEC_XWIDGET)
diff --git a/src/xwidget.h b/src/xwidget.h
index 8c598efb2e2..1b6368daabf 100644
--- a/src/xwidget.h
+++ b/src/xwidget.h
@@ -49,8 +49,7 @@ struct xwidget
 
   /* Vector of currently executing scripts with callbacks.  */
   Lisp_Object script_callbacks;
-
-  /* Here ends the Lisp part.  "height" is the marker field.  */
+  /* Here ends the Lisp part.  script_callbacks is the marker field.  */
 
   int height;
   int width;
@@ -68,8 +67,7 @@ struct xwidget_view
   union vectorlike_header header;
   Lisp_Object model;
   Lisp_Object w;
-
-  /* Here ends the lisp part.  "redisplayed" is the marker field.  */
+  /* Here ends the lisp part.  "w" is the marker field.  */
 
   /* If touched by redisplay.  */
   bool redisplayed;