Revert "Revert "Rely on conservative stack scanning to find "emacs_value"s""

This reverts commit ee7ad83f20903208404a84b58b7a478b62924570.

There was no consensus on reverting
3eb93c07f7a60ac9ce8a16f10c3afd5a3a31243a, so doing that will have to
wait until the discussion ends.

1 files changed, 198 insertions, 175 deletions

diff --git a/src/emacs-module.c b/src/emacs-module.c
index df9a491a864..4e2411cb295 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -25,7 +25,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
-#include <stdlib.h>
 
 #include "lisp.h"
 #include "dynlib.h"
@@ -66,6 +65,18 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include "w32term.h"
 #endif
 
+/* True if Lisp_Object and emacs_value have the same representation.
+   This is typically true unless WIDE_EMACS_INT.  In practice, having
+   the same sizes and alignments and maximums should be a good enough
+   proxy for equality of representation.  */
+enum
+  {
+    plain_values
+      = (sizeof (Lisp_Object) == sizeof (emacs_value)
+         && alignof (Lisp_Object) == alignof (emacs_value)
+         && INTPTR_MAX == EMACS_INT_MAX)
+  };
+
 /* Function prototype for the module init function.  */
 typedef int (*emacs_init_function) (struct emacs_runtime *);
 
@@ -76,43 +87,6 @@ typedef int (*emacs_init_function) (struct emacs_runtime *);
 typedef void (*emacs_finalizer_function) (void *);
 
 
-/* Memory management.  */
-
-/* An `emacs_value' is just a pointer to a structure holding an
-   internal Lisp object.  */
-struct emacs_value_tag { Lisp_Object v; };
-
-/* Local value objects use a simple fixed-sized block allocation
-   scheme without explicit deallocation.  All local values are
-   deallocated when the lifetime of their environment ends.  Keep
-   track of a current frame from which new values are allocated,
-   appending further dynamically-allocated frames if necessary.  */
-
-enum { value_frame_size = 512 };
-
-/* A block from which `emacs_value' object can be allocated.  */
-struct emacs_value_frame
-{
-  /* Storage for values.  */
-  struct emacs_value_tag objects[value_frame_size];
-
-  /* Index of the next free value in `objects'.  */
-  int offset;
-
-  /* Pointer to next frame, if any.  */
-  struct emacs_value_frame *next;
-};
-
-/* A structure that holds an initial frame (so that the first local
-   values require no dynamic allocation) and keeps track of the
-   current frame.  */
-static struct emacs_value_storage
-{
-  struct emacs_value_frame initial;
-  struct emacs_value_frame *current;
-} global_storage;
-
-
 /* Private runtime and environment members.  */
 
 /* The private part of an environment stores the current non local exit state
@@ -125,9 +99,12 @@ struct emacs_env_private
   /* Dedicated storage for non-local exit symbol and data so that
      storage is always available for them, even in an out-of-memory
      situation.  */
-  struct emacs_value_tag non_local_exit_symbol, non_local_exit_data;
+  Lisp_Object non_local_exit_symbol, non_local_exit_data;
 
-  struct emacs_value_storage storage;
+  /* List of values allocated from this environment.  The code uses
+     this only if the user gave the -module-assertions command-line
+     option.  */
+  Lisp_Object values;
 };
 
 /* The private parts of an `emacs_runtime' object contain the initial
@@ -141,7 +118,6 @@ struct emacs_runtime_private
 /* Forward declarations.  */
 
 static Lisp_Object value_to_lisp (emacs_value);
-static emacs_value allocate_emacs_value (emacs_env *, struct emacs_value_storage *, Lisp_Object);
 static emacs_value lisp_to_value (emacs_env *, Lisp_Object);
 static enum emacs_funcall_exit module_non_local_exit_check (emacs_env *);
 static void module_assert_thread (void);
@@ -163,7 +139,16 @@ static void module_non_local_exit_throw_1 (emacs_env *,
 static void module_out_of_memory (emacs_env *);
 static void module_reset_handlerlist (struct handler **);
 
+/* We used to return NULL when emacs_value was a different type from
+   Lisp_Object, but nowadays we just use Qnil instead.  Although they
+   happen to be the same thing in the current implementation, module
+   code should not assume this.  */
+verify (NIL_IS_ZERO);
+static emacs_value const module_nil = 0;
+
 static bool module_assertions = false;
+static emacs_env *global_env;
+static struct emacs_env_private global_env_private;
 
 /* Convenience macros for non-local exit handling.  */
 
@@ -308,7 +293,7 @@ module_get_environment (struct emacs_runtime *ert)
 static emacs_value
 module_make_global_ref (emacs_env *env, emacs_value ref)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   struct Lisp_Hash_Table *h = XHASH_TABLE (Vmodule_refs_hash);
   Lisp_Object new_obj = value_to_lisp (ref);
   EMACS_UINT hashcode;
@@ -328,7 +313,7 @@ module_make_global_ref (emacs_env *env, emacs_value ref)
       hash_put (h, new_obj, make_fixed_natnum (1), hashcode);
     }
 
-  return allocate_emacs_value (env, &global_storage, new_obj);
+  return lisp_to_value (module_assertions ? global_env : env, new_obj);
 }
 
 static void
@@ -356,16 +341,23 @@ module_free_global_ref (emacs_env *env, emacs_value ref)
 
   if (module_assertions)
     {
+      Lisp_Object globals = global_env_private.values;
+      Lisp_Object prev = Qnil;
       ptrdiff_t count = 0;
-      for (struct emacs_value_frame *frame = &global_storage.initial;
-           frame != NULL; frame = frame->next)
+      for (Lisp_Object tail = globals; CONSP (tail);
+           tail = XCDR (tail))
         {
-          for (int i = 0; i < frame->offset; ++i)
+          emacs_value global = xmint_pointer (XCAR (tail));
+          if (global == ref)
             {
-              if (&frame->objects[i] == ref)
-                return;
-              ++count;
+              if (NILP (prev))
+                global_env_private.values = XCDR (globals);
+              else
+                XSETCDR (prev, XCDR (tail));
+              return;
             }
+          ++count;
+          prev = tail;
         }
       module_abort ("Global value was not found in list of %"pD"d globals",
                     count);
@@ -396,8 +388,9 @@ module_non_local_exit_get (emacs_env *env, emacs_value *sym, emacs_value *data)
   struct emacs_env_private *p = env->private_members;
   if (p->pending_non_local_exit != emacs_funcall_exit_return)
     {
-      *sym = &p->non_local_exit_symbol;
-      *data = &p->non_local_exit_data;
+      /* FIXME: lisp_to_value can exit non-locally.  */
+      *sym = lisp_to_value (env, p->non_local_exit_symbol);
+      *data = lisp_to_value (env, p->non_local_exit_data);
     }
   return p->pending_non_local_exit;
 }
@@ -441,7 +434,7 @@ module_make_function (emacs_env *env, ptrdiff_t min_arity, ptrdiff_t max_arity,
                       emacs_subr subr, const char *documentation,
                       void *data)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
 
   if (! (0 <= min_arity
          && (max_arity < 0
@@ -474,7 +467,7 @@ static emacs_value
 module_funcall (emacs_env *env, emacs_value fun, ptrdiff_t nargs,
                 emacs_value args[])
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
 
   /* Make a new Lisp_Object array starting with the function as the
      first arg, because that's what Ffuncall takes.  */
@@ -495,14 +488,14 @@ module_funcall (emacs_env *env, emacs_value fun, ptrdiff_t nargs,
 static emacs_value
 module_intern (emacs_env *env, const char *name)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   return lisp_to_value (env, intern (name));
 }
 
 static emacs_value
 module_type_of (emacs_env *env, emacs_value value)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   return lisp_to_value (env, Ftype_of (value_to_lisp (value)));
 }
 
@@ -535,7 +528,7 @@ module_extract_integer (emacs_env *env, emacs_value n)
 static emacs_value
 module_make_integer (emacs_env *env, intmax_t n)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   return lisp_to_value (env, make_int (n));
 }
 
@@ -551,7 +544,7 @@ module_extract_float (emacs_env *env, emacs_value f)
 static emacs_value
 module_make_float (emacs_env *env, double d)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   return lisp_to_value (env, make_float (d));
 }
 
@@ -588,7 +581,7 @@ module_copy_string_contents (emacs_env *env, emacs_value value, char *buffer,
 static emacs_value
 module_make_string (emacs_env *env, const char *str, ptrdiff_t length)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   if (! (0 <= length && length <= STRING_BYTES_BOUND))
     overflow_error ();
   /* FIXME: AUTO_STRING_WITH_LEN requires STR to be null-terminated,
@@ -601,7 +594,7 @@ module_make_string (emacs_env *env, const char *str, ptrdiff_t length)
 static emacs_value
 module_make_user_ptr (emacs_env *env, emacs_finalizer_function fin, void *ptr)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   return lisp_to_value (env, make_user_ptr (fin, ptr));
 }
 
@@ -663,7 +656,7 @@ module_vec_set (emacs_env *env, emacs_value vec, ptrdiff_t i, emacs_value val)
 static emacs_value
 module_vec_get (emacs_env *env, emacs_value vec, ptrdiff_t i)
 {
-  MODULE_FUNCTION_BEGIN (NULL);
+  MODULE_FUNCTION_BEGIN (module_nil);
   Lisp_Object lvec = value_to_lisp (vec);
   check_vec_index (lvec, i);
   return lisp_to_value (env, AREF (lvec, i));
@@ -706,11 +699,9 @@ module_signal_or_throw (struct emacs_env_private *env)
     case emacs_funcall_exit_return:
       return;
     case emacs_funcall_exit_signal:
-      xsignal (value_to_lisp (&env->non_local_exit_symbol),
-               value_to_lisp (&env->non_local_exit_data));
+      xsignal (env->non_local_exit_symbol, env->non_local_exit_data);
     case emacs_funcall_exit_throw:
-      Fthrow (value_to_lisp (&env->non_local_exit_symbol),
-              value_to_lisp (&env->non_local_exit_data));
+      Fthrow (env->non_local_exit_symbol, env->non_local_exit_data);
     default:
       eassume (false);
     }
@@ -786,12 +777,17 @@ funcall_module (Lisp_Object function, ptrdiff_t nargs, Lisp_Object *arglist)
   record_unwind_protect_ptr (finalize_environment_unwind, env);
 
   USE_SAFE_ALLOCA;
-  emacs_value *args = nargs > 0 ? SAFE_ALLOCA (nargs * sizeof *args) : NULL;
-  for (ptrdiff_t i = 0; i < nargs; ++i)
+  ATTRIBUTE_MAY_ALIAS emacs_value *args;
+  if (plain_values && ! module_assertions)
+    /* FIXME: The cast below is incorrect because the argument array
+       is not declared as const, so module functions can modify it.
+       Either declare it as const, or remove this branch.  */
+    args = (emacs_value *) arglist;
+  else
     {
-      args[i] = lisp_to_value (env, arglist[i]);
-      if (! args[i])
-        memory_full (sizeof *args[i]);
+      args = SAFE_ALLOCA (nargs * sizeof *args);
+      for (ptrdiff_t i = 0; i < nargs; i++)
+        args[i] = lisp_to_value (env, arglist[i]);
     }
 
   emacs_value ret = func->subr (env, nargs, args, func->data);
@@ -871,8 +867,8 @@ module_non_local_exit_signal_1 (emacs_env *env, Lisp_Object sym,
   if (p->pending_non_local_exit == emacs_funcall_exit_return)
     {
       p->pending_non_local_exit = emacs_funcall_exit_signal;
-      p->non_local_exit_symbol.v = sym;
-      p->non_local_exit_data.v = data;
+      p->non_local_exit_symbol = sym;
+      p->non_local_exit_data = data;
     }
 }
 
@@ -884,8 +880,8 @@ module_non_local_exit_throw_1 (emacs_env *env, Lisp_Object tag,
   if (p->pending_non_local_exit == emacs_funcall_exit_return)
     {
       p->pending_non_local_exit = emacs_funcall_exit_throw;
-      p->non_local_exit_symbol.v = tag;
-      p->non_local_exit_data.v = value;
+      p->non_local_exit_symbol = tag;
+      p->non_local_exit_data = value;
     }
 }
 
@@ -902,8 +898,54 @@ module_out_of_memory (emacs_env *env)
 
 /* Value conversion.  */
 
-/* Convert an `emacs_value' to the corresponding internal object.
-   Never fails.  */
+/* We represent Lisp objects differently depending on whether the user
+   gave -module-assertions.  If assertions are disabled, emacs_value
+   objects are Lisp_Objects cast to emacs_value.  If assertions are
+   enabled, emacs_value objects are pointers to Lisp_Object objects
+   allocated from the free store; they are never freed, which ensures
+   that their addresses are unique and can be used for liveness
+   checking.  */
+
+/* Unique Lisp_Object used to mark those emacs_values which are really
+   just containers holding a Lisp_Object that does not fit as an emacs_value,
+   either because it is an integer out of range, or is not properly aligned.
+   Used only if !plain_values.  */
+static Lisp_Object ltv_mark;
+
+/* Convert V to the corresponding internal object O, such that
+   V == lisp_to_value_bits (O).  Never fails.  */
+static Lisp_Object
+value_to_lisp_bits (emacs_value v)
+{
+  if (plain_values || USE_LSB_TAG)
+    return XPL (v);
+
+  /* With wide EMACS_INT and when tag bits are the most significant,
+     reassembling integers differs from reassembling pointers in two
+     ways.  First, save and restore the least-significant bits of the
+     integer, not the most-significant bits.  Second, sign-extend the
+     integer when restoring, but zero-extend pointers because that
+     makes TAG_PTR faster.  */
+
+  intptr_t i = (intptr_t) v;
+  EMACS_UINT tag = i & ((1 << GCTYPEBITS) - 1);
+  EMACS_UINT untagged = i - tag;
+  switch (tag)
+    {
+    case_Lisp_Int:
+      {
+        bool negative = tag & 1;
+        EMACS_UINT sign_extension
+          = negative ? VALMASK & ~(INTPTR_MAX >> INTTYPEBITS): 0;
+        uintptr_t u = i;
+        intptr_t all_but_sign = u >> GCTYPEBITS;
+        untagged = sign_extension + all_but_sign;
+        break;
+      }
+    }
+
+  return XIL ((tag << VALBITS) + untagged);
+}
 
 /* If V was computed from lisp_to_value (O), then return O.
    Exits non-locally only if the stack overflows.  */
@@ -914,134 +956,91 @@ value_to_lisp (emacs_value v)
     {
       /* Check the liveness of the value by iterating over all live
          environments.  */
+      void *vptr = v;
+      ATTRIBUTE_MAY_ALIAS Lisp_Object *optr = vptr;
       ptrdiff_t num_environments = 0;
       ptrdiff_t num_values = 0;
       for (Lisp_Object environments = Vmodule_environments;
            CONSP (environments); environments = XCDR (environments))
         {
           emacs_env *env = xmint_pointer (XCAR (environments));
-          struct emacs_env_private *priv = env->private_members;
-          /* The value might be one of the nonlocal exit values.  Note
-             that we don't check whether a nonlocal exit is currently
-             pending, because the module might have cleared the flag
-             in the meantime.  */
-          if (&priv->non_local_exit_symbol == v
-              || &priv->non_local_exit_data == v)
-            goto ok;
-          for (struct emacs_value_frame *frame = &priv->storage.initial;
-               frame != NULL; frame = frame->next)
+          for (Lisp_Object values = env->private_members->values;
+               CONSP (values); values = XCDR (values))
             {
-              for (int i = 0; i < frame->offset; ++i)
-                {
-                  if (&frame->objects[i] == v)
-                    goto ok;
-                  ++num_values;
-                }
-            }
-          ++num_environments;
-        }
-      /* Also check global values.  */
-      for (struct emacs_value_frame *frame = &global_storage.initial;
-           frame != NULL; frame = frame->next)
-        {
-          for (int i = 0; i < frame->offset; ++i)
-            {
-              if (&frame->objects[i] == v)
-                goto ok;
+              Lisp_Object *p = xmint_pointer (XCAR (values));
+              if (p == optr)
+                return *p;
               ++num_values;
             }
+          ++num_environments;
         }
       module_abort (("Emacs value not found in %"pD"d values "
                      "of %"pD"d environments"),
                     num_values, num_environments);
     }
 
- ok: return v->v;
+  Lisp_Object o = value_to_lisp_bits (v);
+  if (! plain_values && CONSP (o) && EQ (XCDR (o), ltv_mark))
+    o = XCAR (o);
+  return o;
 }
 
-/* Convert an internal object to an `emacs_value'.  Allocate storage
-   from the environment; return NULL if allocation fails.  */
+/* Attempt to convert O to an emacs_value.  Do not do any checking
+   or allocate any storage; the caller should prevent or detect
+   any resulting bit pattern that is not a valid emacs_value.  */
 static emacs_value
-lisp_to_value (emacs_env *env, Lisp_Object o)
+lisp_to_value_bits (Lisp_Object o)
 {
-  struct emacs_env_private *p = env->private_members;
-  if (p->pending_non_local_exit != emacs_funcall_exit_return)
-    return NULL;
-  return allocate_emacs_value (env, &p->storage, o);
-}
+  if (plain_values || USE_LSB_TAG)
+    return XLP (o);
 
-/* Must be called for each frame before it can be used for allocation.  */
-static void
-initialize_frame (struct emacs_value_frame *frame)
-{
-  frame->offset = 0;
-  frame->next = NULL;
-}
-
-/* Must be called for any storage object before it can be used for
-   allocation.  */
-static void
-initialize_storage (struct emacs_value_storage *storage)
-{
-  initialize_frame (&storage->initial);
-  storage->current = &storage->initial;
-}
-
-/* Must be called for any initialized storage object before its
-   lifetime ends.  Free all dynamically-allocated frames.  */
-static void
-finalize_storage (struct emacs_value_storage *storage)
-{
-  struct emacs_value_frame *next = storage->initial.next;
-  while (next != NULL)
+  /* Compress O into the space of a pointer, possibly losing information.  */
+  EMACS_UINT u = XLI (o);
+  if (FIXNUMP (o))
     {
-      struct emacs_value_frame *current = next;
-      next = current->next;
-      free (current);
+      uintptr_t i = (u << VALBITS) + XTYPE (o);
+      return (emacs_value) i;
+    }
+  else
+    {
+      char *p = XLP (o);
+      void *v = p - (u & ~VALMASK) + XTYPE (o);
+      return v;
     }
 }
 
-/* Allocate a new value from STORAGE and stores OBJ in it.  Return
-   NULL if allocation fails and use ENV for non local exit reporting.  */
+/* Convert O to an emacs_value.  Allocate storage if needed; this can
+   signal if memory is exhausted.  Must be an injective function.  */
 static emacs_value
-allocate_emacs_value (emacs_env *env, struct emacs_value_storage *storage,
-                      Lisp_Object obj)
+lisp_to_value (emacs_env *env, Lisp_Object o)
 {
-  eassert (storage->current);
-  eassert (storage->current->offset < value_frame_size);
-  eassert (! storage->current->next);
-  if (storage->current->offset == value_frame_size - 1)
+  if (module_assertions)
     {
-      storage->current->next = malloc (sizeof *storage->current->next);
-      if (! storage->current->next)
-        {
-          module_out_of_memory (env);
-          return NULL;
-        }
-      initialize_frame (storage->current->next);
-      storage->current = storage->current->next;
+      /* Add the new value to the list of values allocated from this
+         environment.  The value is actually a pointer to the
+         Lisp_Object cast to emacs_value.  We make a copy of the
+         object on the free store to guarantee unique addresses.  */
+      ATTRIBUTE_MAY_ALIAS Lisp_Object *optr = xmalloc (sizeof o);
+      *optr = o;
+      void *vptr = optr;
+      ATTRIBUTE_MAY_ALIAS emacs_value ret = vptr;
+      struct emacs_env_private *priv = env->private_members;
+      priv->values = Fcons (make_mint_ptr (ret), priv->values);
+      return ret;
     }
-  emacs_value value = storage->current->objects + storage->current->offset;
-  value->v = obj;
-  ++storage->current->offset;
-  return value;
-}
 
-/* Mark all objects allocated from local environments so that they
-   don't get garbage-collected.  */
-void
-mark_modules (void)
-{
-  for (Lisp_Object tem = Vmodule_environments; CONSP (tem); tem = XCDR (tem))
+  emacs_value v = lisp_to_value_bits (o);
+
+  if (! EQ (o, value_to_lisp_bits (v)))
     {
-      emacs_env *env = xmint_pointer (XCAR (tem));
-      struct emacs_env_private *priv = env->private_members;
-      for (struct emacs_value_frame *frame = &priv->storage.initial;
-           frame != NULL;
-           frame = frame->next)
-        for (int i = 0; i < frame->offset; ++i)
-          mark_object (frame->objects[i].v);
+      /* Package the incompressible object pointer inside a pair
+         that is compressible.  */
+      Lisp_Object pair = Fcons (o, ltv_mark);
+      v = (emacs_value) ((intptr_t) XCONS (pair) + Lisp_Cons);
     }
+
+  eassert (EQ (o, value_to_lisp (v)));
+  return v;
 }
 
 
@@ -1060,7 +1059,7 @@ initialize_environment (emacs_env *env, struct emacs_env_private *priv)
       env = xmalloc (sizeof *env);
 
   priv->pending_non_local_exit = emacs_funcall_exit_return;
-  initialize_storage (&priv->storage);
+  priv->values = priv->non_local_exit_symbol = priv->non_local_exit_data = Qnil;
   env->size = sizeof *env;
   env->private_members = priv;
   env->make_global_ref = module_make_global_ref;
@@ -1101,9 +1100,11 @@ initialize_environment (emacs_env *env, struct emacs_env_private *priv)
 static void
 finalize_environment (emacs_env *env)
 {
-  finalize_storage (&env->private_members->storage);
   eassert (xmint_pointer (XCAR (Vmodule_environments)) == env);
   Vmodule_environments = XCDR (Vmodule_environments);
+  if (module_assertions)
+    /* There is always at least the global environment.  */
+    eassert (CONSP (Vmodule_environments));
 }
 
 static void
@@ -1121,6 +1122,20 @@ finalize_runtime_unwind (void *raw_ert)
   finalize_environment (ert->private_members->env);
 }
 
+void
+mark_modules (void)
+{
+  for (Lisp_Object tail = Vmodule_environments; CONSP (tail);
+       tail = XCDR (tail))
+    {
+      emacs_env *env = xmint_pointer (XCAR (tail));
+      struct emacs_env_private *priv = env->private_members;
+      mark_object (priv->non_local_exit_symbol);
+      mark_object (priv->non_local_exit_data);
+      mark_object (priv->values);
+    }
+}
+
 
 /* Non-local exit handling.  */
 
@@ -1160,7 +1175,8 @@ init_module_assertions (bool enable)
   /* If enabling module assertions, use a hidden environment for
      storing the globals.  This environment is never freed.  */
   module_assertions = enable;
-  initialize_storage (&global_storage);
+  if (enable)
+    global_env = initialize_environment (NULL, &global_env_private);
 }
 
 static _Noreturn void
@@ -1183,6 +1199,13 @@ module_abort (const char *format, ...)
 void
 syms_of_module (void)
 {
+  if (!plain_values)
+    {
+      ltv_mark = Fcons (Qnil, Qnil);
+      staticpro (&ltv_mark);
+    }
+  eassert (NILP (value_to_lisp (module_nil)));
+
   DEFSYM (Qmodule_refs_hash, "module-refs-hash");
   DEFVAR_LISP ("module-refs-hash", Vmodule_refs_hash,
                doc: /* Module global reference table.  */);