Bug#37075: offset of limit clause might be truncated on 32-bits server w/o big tables

The problem is that the offset argument of the limit clause
might be truncated on a 32-bits server built without big
tables support. The truncation was happening because the
original 64-bits long argument was being cast to a 32-bits
(ha_rows) offset counter.

The solution is to check if the conversing resulted in value
truncation and if so, the offset is set to the maximum possible
value that can fit on the type.

mysql-test/r/limit.result:
  Add test case result for Bug#37075
mysql-test/t/limit.test:
  Add test case for Bug#37075
sql/sql_lex.cc:
  Check for truncation of the offset value. If value was
  truncated, set to the maximum possible value.

mysql-test/r/limit.result

@@ -111,3 +111,6 @@ set @a=-14632475938453979136;
 execute s using @a, @a;
 ERROR HY000: Incorrect arguments to EXECUTE
 End of 5.0 tests
+select 1 as a limit 4294967296,10;
+a
+End of 5.1 tests

mysql-test/t/limit.test

@@ -95,3 +95,11 @@ set @a=-14632475938453979136;
 execute s using @a, @a;
 
 --echo End of 5.0 tests
+
+#
+# Bug#37075: offset of limit clause might be truncated to 0 on 32-bits server w/o big tables
+#
+
+select 1 as a limit 4294967296,10;
+
+--echo End of 5.1 tests

sql/sql_lex.cc

@@ -2041,12 +2041,26 @@ st_lex::copy_db_to(char **p_db, uint *p_db_length) const
 void st_select_lex_unit::set_limit(SELECT_LEX *sl)
 {
   ha_rows select_limit_val;
+  ulonglong val;
 
   DBUG_ASSERT(! thd->stmt_arena->is_stmt_prepare());
-  select_limit_val= (ha_rows)(sl->select_limit ? sl->select_limit->val_uint() :
-                                                 HA_POS_ERROR);
-  offset_limit_cnt= (ha_rows)(sl->offset_limit ? sl->offset_limit->val_uint() :
-                                                 ULL(0));
+  val= sl->select_limit ? sl->select_limit->val_uint() : HA_POS_ERROR;
+  select_limit_val= (ha_rows)val;
+#ifndef BIG_TABLES
+  /*
+    Check for overflow : ha_rows can be smaller then ulonglong if
+    BIG_TABLES is off.
+    */
+  if (val != (ulonglong)select_limit_val)
+    select_limit_val= HA_POS_ERROR;
+#endif
+  val= sl->offset_limit ? sl->offset_limit->val_uint() : ULL(0);
+  offset_limit_cnt= (ha_rows)val;
+#ifndef BIG_TABLES
+  /* Check for truncation. */
+  if (val != (ulonglong)offset_limit_cnt)
+    offset_limit_cnt= HA_POS_ERROR;
+#endif
   select_limit_cnt= select_limit_val + offset_limit_cnt;
   if (select_limit_cnt < select_limit_val)
     select_limit_cnt= HA_POS_ERROR;		// no limit