Use objdump to produce an assembler listing, but which includes the machine byte representation of each instruction (redirect output to a different .s file):

        $ objdump -d mycode.o >mycode_obj.s
     

Here is mycoe_obj.s

   0:   68 ac 3d 04 08          push   $0x8043dac
   5:   68 00 05 40 fd          push   $0xfd400500
   a:   89 e5                   mov    %esp,%ebp
   c:   b8 05 00 00 00          mov    $0x5,%eax
  11:   5d                      pop    %ebp
  12:   c3                      ret

The machine program code is 18 (0x12) bytes long and (ignoring blanks) is:

68 ac 3d 04 08 68 00 05 40 fd 89 e5 b8 05 00 00 00 5d c3