Bug#38999 valgrind warnings for update statement in function compare_record()

Valgrind warning happpens because of uninitialized null bytes.
In row_sel_push_cache_row_for_mysql() function we fill fetch cache
with necessary field values, row_sel_store_mysql_rec() is called
for this and leaves null bytes untouched.
Later row_sel_pop_cached_row_for_mysql() rewrites table record
buffer with uninited null bytes. We can see the problem from the
test case:
At 'SELECT...' we call row_sel_push...->row_sel_store...->row_sel_pop_cached...
chain which rewrites table->record[0] buffer with uninitialized null bytes.
When we call 'UPDATE...' statement, compare_record uses this buffer and
valgrind warning occurs.
The fix is to init null bytes with default values.

mysql-test/suite/innodb/r/innodb_mysql.result

@@ -2378,4 +2378,16 @@ SELECT SECOND(c)-@bug47453 FROM t1 JOIN t2 ON d=a;
 SECOND(c)-@bug47453
 0
 DROP TABLE t1, t2;
+#
+# Bug#38999 valgrind warnings for update statement in function compare_record()
+#
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 values (1),(2),(3),(4),(5);
+INSERT INTO t2 values (1);
+SELECT * FROM t1 WHERE a = 2;
+a
+2
+UPDATE t1,t2 SET t1.a = t1.a + 100 WHERE t1.a = 1;
+DROP TABLE t1,t2;
 End of 5.1 tests

mysql-test/suite/innodb/t/innodb_mysql.test

@@ -618,5 +618,18 @@ SELECT SECOND(c)-@bug47453 FROM t1 JOIN t2 ON d=a;
 
 DROP TABLE t1, t2;
 
+--echo #
+--echo # Bug#38999 valgrind warnings for update statement in function compare_record()
+--echo #
+
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 values (1),(2),(3),(4),(5);
+INSERT INTO t2 values (1);
+
+SELECT * FROM t1 WHERE a = 2;
+UPDATE t1,t2 SET t1.a = t1.a + 100 WHERE t1.a = 1;
+
+DROP TABLE t1,t2;
 
 --echo End of 5.1 tests

mysql-test/t/ps_3innodb.test

@@ -8,10 +8,6 @@
 # NOTE: PLEASE SEE ps_1general.test (bottom) 
 #       BEFORE ADDING NEW TEST CASES HERE !!!
 
-# See Bug#38999 valgrind warnings for update statement in function
-# compare_record()
--- source include/not_valgrind.inc
-
 use test;
 
 -- source include/have_innodb.inc

storage/innobase/row/row0sel.c

@@ -2621,6 +2621,12 @@ row_sel_store_mysql_rec(
 		prebuilt->blob_heap = NULL;
 	}
 
+	/* init null bytes with default values as they might be
+	left uninitialized in some cases and this uninited bytes
+	might be copied into mysql record buffer that leads to
+	valgrind warnings */
+	memcpy(mysql_rec, prebuilt->default_rec, prebuilt->null_bitmap_len);
+
 	for (i = 0; i < prebuilt->n_template; i++) {
 
 		templ = prebuilt->mysql_template + i;