Don't copy uninitialized bytes when copying varstrings

When using field_conv(), which is called in case of field1=field2 copy in
fill_records(), full varstring's was copied, including unitialized bytes.
This caused valgrind to compilain about usage of unitialized bytes when
using Aria static length records.
Fixed by not using memcpy when copying varstrings but instead just copy
the real bytes.

sql/field.cc

@@ -7613,6 +7613,17 @@ int Field_varstring::save_field_metadata(uchar *metadata_ptr)
   return 2;
 }
 
+
+bool Field_varstring::memcpy_field_possible(const Field *from) const
+{
+  return (Field_str::memcpy_field_possible(from) &&
+          !compression_method() == !from->compression_method() &&
+          length_bytes == ((Field_varstring*) from)->length_bytes &&
+          (table->file && !(table->file->ha_table_flags() &
+                            HA_RECORD_MUST_BE_CLEAN_ON_WRITE)));
+}
+
+
 int Field_varstring::store(const char *from,size_t length,CHARSET_INFO *cs)
 {
   ASSERT_COLUMN_MARKED_FOR_WRITE_OR_COMPUTED;

sql/field.h

@@ -3463,12 +3463,7 @@ class Field_varstring :public Field_longstr {
                                     length_bytes : 0);
   }
   Copy_func *get_copy_func(const Field *from) const;
-  bool memcpy_field_possible(const Field *from) const
-  {
-    return Field_str::memcpy_field_possible(from) &&
-           !compression_method() == !from->compression_method() &&
-           length_bytes == ((Field_varstring*) from)->length_bytes;
-  }
+  bool memcpy_field_possible(const Field *from) const;
   int  store(const char *to,size_t length,CHARSET_INFO *charset);
   using Field_str::store;
 #ifdef HAVE_valgrind_or_MSAN

sql/handler.h

@@ -200,7 +200,8 @@ enum enum_alter_inplace_result {
 #define HA_HAS_NEW_CHECKSUM    (1ULL << 38)
 #define HA_CAN_VIRTUAL_COLUMNS (1ULL << 39)
 #define HA_MRR_CANT_SORT       (1ULL << 40)
-#define HA_RECORD_MUST_BE_CLEAN_ON_WRITE (1ULL << 41) /* unused */
+/* All of VARCHAR is stored, including bytes after real varchar data */
+#define HA_RECORD_MUST_BE_CLEAN_ON_WRITE (1ULL << 41)
 
 /*
   This storage engine supports condition pushdown

storage/maria/ha_maria.cc

@@ -1162,7 +1162,7 @@ int ha_maria::open(const char *name, int mode, uint test_if_locked)
     that all bytes in the row is properly reset.
   */
   if (file->s->data_file_type == STATIC_RECORD &&
-      (file->s->has_varchar_fields | file->s->has_null_fields))
+      (file->s->has_varchar_fields || file->s->has_null_fields))
     int_table_flags|= HA_RECORD_MUST_BE_CLEAN_ON_WRITE;
 
   for (i= 0; i < table->s->keys; i++)

storage/myisam/ha_myisam.cc

@@ -863,8 +863,9 @@ int ha_myisam::open(const char *name, int mode, uint test_if_locked)
     the full row to ensure we don't get any errors from valgrind and
     that all bytes in the row is properly reset.
   */
-  if ((file->s->options & HA_OPTION_PACK_RECORD) &&
-      (file->s->has_varchar_fields | file->s->has_null_fields))
+  if (!(file->s->options &
+        (HA_OPTION_PACK_RECORD | HA_OPTION_COMPRESS_RECORD)) &&
+      (file->s->has_varchar_fields || file->s->has_null_fields))
     int_table_flags|= HA_RECORD_MUST_BE_CLEAN_ON_WRITE;
 
   for (i= 0; i < table->s->keys; i++)