libdl: Add object file dependencies to track references

Tracking references lets us manage when an object file can be
unloaded. If an object file has references to it, it cannot be
unloaded.

Modules that depend on each other cannot be unloaded.

Updates #3605

cpukit/libdl/rtl-obj.c

@@ -83,6 +83,7 @@ rtems_rtl_obj_alloc (void)
      * Initialise the chains.
      */
     rtems_chain_initialize_empty (&obj->sections);
+    rtems_chain_initialize_empty (&obj->dependents);
     /*
      * No valid format.
      */
@@ -114,6 +115,8 @@ rtems_rtl_obj_free (rtems_rtl_obj* obj)
     rtems_chain_extract (&obj->link);
   rtems_rtl_alloc_module_del (&obj->text_base, &obj->const_base, &obj->eh_base,
                               &obj->data_base, &obj->bss_base);
+  rtems_rtl_obj_erase_sections (obj);
+  rtems_rtl_obj_erase_dependents (obj);
   rtems_rtl_symbol_obj_erase (obj);
   rtems_rtl_obj_free_names (obj);
   if (obj->sec_num)
@@ -550,6 +553,110 @@ rtems_rtl_obj_find_section_by_mask (const rtems_rtl_obj* obj,
   return match.sect;
 }
 
+bool
+rtems_rtl_obj_alloc_dependents (rtems_rtl_obj* obj, size_t dependents)
+{
+  rtems_rtl_obj_depends* depends;
+  size_t                 size;
+
+  size = sizeof (rtems_rtl_obj_depends) + sizeof (rtems_rtl_obj*) * dependents;
+
+  depends = rtems_rtl_alloc_new (RTEMS_RTL_ALLOC_OBJECT,
+                                 size,
+                                 true);
+  if (depends == NULL)
+  {
+    rtems_rtl_set_error (ENOMEM, "no memory for the dependency");
+  }
+  else
+  {
+    depends->dependents = dependents;
+    rtems_chain_append (&obj->dependents, &depends->node);
+  }
+
+  return depends != NULL;
+}
+
+void
+rtems_rtl_obj_erase_dependents (rtems_rtl_obj* obj)
+{
+  rtems_chain_node* node = rtems_chain_first (&obj->dependents);
+  while (!rtems_chain_is_tail (&obj->dependents, node))
+  {
+    rtems_rtl_obj_depends* depends = (rtems_rtl_obj_depends*) node;
+    rtems_chain_node*      next_node = rtems_chain_next (node);
+    rtems_chain_extract (node);
+    rtems_rtl_alloc_del (RTEMS_RTL_ALLOC_OBJECT, depends);
+    node = next_node;
+  }
+}
+
+bool
+rtems_rtl_obj_add_dependent (rtems_rtl_obj* obj, rtems_rtl_obj* dependent)
+{
+  rtems_rtl_obj**   free_slot;
+  rtems_chain_node* node;
+  if (obj == dependent || dependent == rtems_rtl_baseimage ())
+    return false;
+  free_slot = NULL;
+  node = rtems_chain_first (&obj->dependents);
+  while (!rtems_chain_is_tail (&obj->dependents, node))
+  {
+    rtems_rtl_obj_depends* depends = (rtems_rtl_obj_depends*) node;
+    size_t                 d;
+    for (d = 0; d < depends->dependents; ++d)
+    {
+      if (free_slot == NULL && depends->depends[d] == NULL)
+        free_slot = &(depends->depends[d]);
+      if (depends->depends[d] == dependent)
+        return false;
+    }
+    node = rtems_chain_next (node);
+  }
+  if (free_slot == NULL)
+  {
+    if (rtems_rtl_obj_alloc_dependents (obj,
+                                        RTEMS_RTL_DEPENDENCY_BLOCK_SIZE))
+    {
+      rtems_rtl_obj_depends* depends;
+      node = rtems_chain_last (&obj->dependents);
+      depends = (rtems_rtl_obj_depends*) node;
+      free_slot = &(depends->depends[0]);
+      if (*free_slot != NULL)
+      {
+        rtems_rtl_set_error (EINVAL, "new dependency node not empty");
+        free_slot = NULL;
+      }
+    }
+  }
+  if (free_slot != NULL)
+    *free_slot = dependent;
+  return free_slot != NULL;
+}
+
+bool
+rtems_rtl_obj_iterate_dependents (rtems_rtl_obj*                 obj,
+                                  rtems_rtl_obj_depends_iterator iterator,
+                                  void*                          data)
+{
+  rtems_chain_node* node = rtems_chain_first (&obj->dependents);
+  while (!rtems_chain_is_tail (&obj->dependents, node))
+  {
+    rtems_rtl_obj_depends* depends = (rtems_rtl_obj_depends*) node;
+    size_t                 d;
+    for (d = 0; d < depends->dependents; ++d)
+    {
+      if (depends->depends[d])
+      {
+        if (iterator (obj, depends->depends[d], data))
+          return true;
+      }
+    }
+    node = rtems_chain_next (node);
+  }
+  return false;
+}
+
 size_t
 rtems_rtl_obj_text_size (const rtems_rtl_obj* obj)
 {
@@ -1220,10 +1327,42 @@ static bool
 rtems_rtl_obj_file_unload (rtems_rtl_obj* obj)
 {
   if (obj->format >= 0 && obj->format < RTEMS_RTL_LOADERS)
-      return loaders[obj->format].unload (obj);
+  {
+    rtems_chain_node* node;
+
+    if (!loaders[obj->format].unload (obj))
+      return false;
+
+    node = rtems_chain_first (&obj->dependents);
+    while (!rtems_chain_is_tail (&obj->dependents, node))
+    {
+      rtems_rtl_obj_depends* depends = (rtems_rtl_obj_depends*) node;
+      size_t                 d;
+      for (d = 0; d < depends->dependents; ++d)
+      {
+        if (depends->depends[d] != NULL)
+          rtems_rtl_obj_dec_reference (depends->depends[d]);
+      }
+      node = rtems_chain_next (node);
+    }
+  }
+
   return false;
 }
 
+void
+rtems_rtl_obj_inc_reference (rtems_rtl_obj* obj)
+{
+  ++obj->refs;
+}
+
+void
+rtems_rtl_obj_dec_reference (rtems_rtl_obj* obj)
+{
+  if (obj->refs)
+    --obj->refs;
+}
+
 bool
 rtems_rtl_obj_load (rtems_rtl_obj* obj)
 {