Problem:-
We have created a table with UTF8_BIN collation.
In case, when in our query we have ORDER BY clause over a function 
call we are getting result in incorrect order.
Note:the bug is not there in 5.5.

Analysis:
In 5.5, for UTF16_BIN, we have min and max multi-byte length is 2 and 4 
respectively.In make_sortkey(),for 2 byte character character we are 
assuming that the resultant length will be 2 byte/character. But when we 
use my_strnxfrm_unicode_full_bin(), we store sorting weights using 3 bytes 
per character.This result in truncated result.

Same thing happen for UTF8MB4, where we have 1 byte min multi-byte and 
4 byte max multi-byte.We will accsume resultant data as 1 byte/character, 
which result in truncated result.

Solution:-
use strnxfrm(means use of MY_CS_STRNXFRM macro) is used for sort, in 
which the resultant length is not dependent on source length.