Bug#13871079 RQG_MYISAM_DML_ALTER_VALGRIND FAILS ON VALGRIND PN PB2

The class Copy_field contains a String tmp, 
which may allocate memory on the heap.
That means that all instances of Copy_field
must be properly destroyed. Alas they are not.

Solution: don't use Copy_field::tmp for copying
from_field => tmp => to_field
in do_field_string()

1 files changed, 13 insertions, 1 deletions

diff --git a/sql/field.cc b/sql/field.cc
index 59eb83da5fa..c7f19976260 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -8257,7 +8257,19 @@ String *Field_set::val_str(String *val_buffer,
   ulonglong tmp=(ulonglong) Field_enum::val_int();
   uint bitnr=0;
 
-  val_buffer->set("", 0, field_charset);
+  if (tmp == 0)
+  {
+    /*
+      Some callers expect *val_buffer to contain the result,
+      so we assign to it, rather than doing 'return &empty_set_string.
+     */
+    *val_buffer= empty_set_string;
+    return val_buffer;
+  }
+
+  val_buffer->set_charset(field_charset);
+  val_buffer->length(0);
+
   while (tmp && bitnr < (uint) typelib->count)
   {
     if (tmp & 1)