Bug#42733: Type-punning warnings when compiling MySQL --

            strict aliasing violations.

One somewhat major source of strict-aliasing violations and
related warnings is the SQL_LIST structure. For example,
consider its member function `link_in_list` which takes
a pointer to pointer of type T (any type) as a pointer to
pointer to unsigned char. Dereferencing this pointer, which
is done to reset the next field, violates strict-aliasing
rules and might cause problems for surrounding code that
uses the next field of the object being added to the list.

The solution is to use templates to parametrize the SQL_LIST
structure in order to deference the pointers with compatible
types. As a side bonus, it becomes possible to remove quite
a few casts related to acessing data members of SQL_LIST.

1 files changed, 10 insertions, 14 deletions

diff --git a/sql/sp.cc b/sql/sp.cc
index ef69edb96c6..e0c1fcfa378 100644
--- a/sql/sp.cc
+++ b/sql/sp.cc
@@ -1630,8 +1630,7 @@ extern "C" uchar* sp_sroutine_key(const uchar *ptr, size_t *plen,
 void sp_get_prelocking_info(THD *thd, bool *need_prelocking, 
                             bool *first_no_prelocking)
 {
-  Sroutine_hash_entry *routine;
-  routine= (Sroutine_hash_entry*)thd->lex->sroutines_list.first;
+  Sroutine_hash_entry *routine= thd->lex->sroutines_list.first;
 
   DBUG_ASSERT(routine);
   bool first_is_procedure= (routine->key.str[0] == TYPE_ENUM_PROCEDURE);
@@ -1694,7 +1693,7 @@ static bool add_used_routine(LEX *lex, Query_arena *arena,
     memcpy(rn->key.str, key->str, key->length + 1);
     if (my_hash_insert(&lex->sroutines, (uchar *)rn))
       return FALSE;
-    lex->sroutines_list.link_in_list((uchar *)rn, (uchar **)&rn->next);
+    lex->sroutines_list.link_in_list(rn, &rn->next);
     rn->belong_to_view= belong_to_view;
     return TRUE;
   }
@@ -1740,7 +1739,7 @@ void sp_add_used_routine(LEX *lex, Query_arena *arena,
 void sp_remove_not_own_routines(LEX *lex)
 {
   Sroutine_hash_entry *not_own_rt, *next_rt;
-  for (not_own_rt= *(Sroutine_hash_entry **)lex->sroutines_list_own_last;
+  for (not_own_rt= *lex->sroutines_list_own_last;
        not_own_rt; not_own_rt= next_rt)
   {
     /*
@@ -1751,7 +1750,7 @@ void sp_remove_not_own_routines(LEX *lex)
     hash_delete(&lex->sroutines, (uchar *)not_own_rt);
   }
 
-  *(Sroutine_hash_entry **)lex->sroutines_list_own_last= NULL;
+  *lex->sroutines_list_own_last= NULL;
   lex->sroutines_list.next= lex->sroutines_list_own_last;
   lex->sroutines_list.elements= lex->sroutines_list_own_elements;
 }
@@ -1832,11 +1831,11 @@ sp_update_stmt_used_routines(THD *thd, LEX *lex, HASH *src,
     It will also add elements to end of 'LEX::sroutines_list' list.
 */
 
-static void sp_update_stmt_used_routines(THD *thd, LEX *lex, SQL_LIST *src,
+static void sp_update_stmt_used_routines(THD *thd, LEX *lex,
+                                         SQL_I_List<Sroutine_hash_entry> *src,
                                          TABLE_LIST *belong_to_view)
 {
-  for (Sroutine_hash_entry *rt= (Sroutine_hash_entry *)src->first;
-       rt; rt= rt->next)
+  for (Sroutine_hash_entry *rt= src->first; rt; rt= rt->next)
     (void)add_used_routine(lex, thd->stmt_arena, &rt->key, belong_to_view);
 }
 
@@ -1971,8 +1970,7 @@ int
 sp_cache_routines_and_add_tables(THD *thd, LEX *lex, bool first_no_prelock)
 {
   return sp_cache_routines_and_add_tables_aux(thd, lex,
-           (Sroutine_hash_entry *)lex->sroutines_list.first,
-           first_no_prelock);
+           lex->sroutines_list.first, first_no_prelock);
 }
 
 
@@ -1996,8 +1994,7 @@ sp_cache_routines_and_add_tables(THD *thd, LEX *lex, bool first_no_prelock)
 int
 sp_cache_routines_and_add_tables_for_view(THD *thd, LEX *lex, TABLE_LIST *view)
 {
-  Sroutine_hash_entry **last_cached_routine_ptr=
-                          (Sroutine_hash_entry **)lex->sroutines_list.next;
+  Sroutine_hash_entry **last_cached_routine_ptr= lex->sroutines_list.next;
   sp_update_stmt_used_routines(thd, lex, &view->view->sroutines_list,
                                view->top_table());
   return sp_cache_routines_and_add_tables_aux(thd, lex,
@@ -2026,8 +2023,7 @@ sp_cache_routines_and_add_tables_for_triggers(THD *thd, LEX *lex,
 {
   int ret= 0;
 
-  Sroutine_hash_entry **last_cached_routine_ptr=
-    (Sroutine_hash_entry **)lex->sroutines_list.next;
+  Sroutine_hash_entry **last_cached_routine_ptr= lex->sroutines_list.next;
 
   if (static_cast<int>(table->lock_type) >=
       static_cast<int>(TL_WRITE_ALLOW_WRITE))