buckport to 5.1.26 from 6.0

Bug#35658 (An empty binary value leads to mysqld crash)
  
Before this fix, the following token
  b''
caused the parser to crash when reading the binary value from the empty string.
The crash was caused by:
  ptr+= max_length - 1;
because max_length is unsigned and was 0, causing an overflow.
  
With this fix, an empty binary literal b'' is parsed as a binary value 0,
in Item_bin_string.

mysql-test/r/varbinary.result

@@ -95,3 +95,34 @@ table_28127_b	CREATE TABLE `table_28127_b` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table table_28127_a;
 drop table table_28127_b;
+select 0b01000001;
+0b01000001
+A
+select 0x41;
+0x41
+A
+select b'01000001';
+b'01000001'
+A
+select x'41', 0+x'41';
+x'41'	0+x'41'
+A	65
+select N'abc', length(N'abc');
+abc	length(N'abc')
+abc	3
+select N'', length(N'');
+	length(N'')
+	0
+select '', length('');
+	length('')
+	0
+select b'', 0+b'';
+b''	0+b''
+	0
+select x'', 0+x'';
+x''	0+x''
+	0
+select 0x;
+ERROR 42S22: Unknown column '0x' in 'field list'
+select 0b;
+ERROR 42S22: Unknown column '0b' in 'field list'

mysql-test/t/varbinary.test

@@ -104,3 +104,31 @@ show create table table_28127_b;
 drop table table_28127_a;
 drop table table_28127_b;
 
+#
+# Bug#35658 (An empty binary value leads to mysqld crash)
+#
+
+select 0b01000001;
+
+select 0x41;
+
+select b'01000001';
+
+select x'41', 0+x'41';
+
+select N'abc', length(N'abc');
+
+select N'', length(N'');
+
+select '', length('');
+
+select b'', 0+b'';
+
+select x'', 0+x'';
+
+--error ER_BAD_FIELD_ERROR
+select 0x;
+
+--error ER_BAD_FIELD_ERROR
+select 0b;
+

sql/item.cc

@@ -5172,6 +5172,9 @@ Item_bin_string::Item_bin_string(const char *str, uint str_length)
   if (!ptr)
     return;
   str_value.set(ptr, max_length, &my_charset_bin);
+
+  if (max_length > 0)
+  {
     ptr+= max_length - 1;
     ptr[1]= 0;                     // Set end null for string
     for (; end >= str; end--)
@@ -5187,6 +5190,10 @@ Item_bin_string::Item_bin_string(const char *str, uint str_length)
       power<<= 1;
     }
     *ptr= (char) bits;
+  }
+  else
+    ptr[0]= 0;
+
   collation.set(&my_charset_bin, DERIVATION_COERCIBLE);
   fixed= 1;
 }