CMPXCHG8B - x86-64 instruction reference

cmpxchg8bCompare and exchange 8 bytes 
Compares the 8-byte value in memory with edx:eax; if equal, stores ecx:ebx there and sets ZF, otherwise loads it into edx:eax.
Pentium and later·takes lock
Intel's reference: CMPXCHG8B/CMPXCHG16B 
CFPFAFZFSFDFOF –––●–––
● set from the result
– not changed
Forms  cmpxchg8b   
Operands mem64 A 64-bit value in memory, for example qword [rbx+8]. 
If they are equal, it sets the zero flag and
stores ECX:EBX into the memory area. If they are unequal, it
clears the zero flag and stores the memory contents into EDX:EAX.
CMPXCHG8B can be used with the LOCK prefix, to allow atomic
execution. This is useful in multi-processor and multi-tasking
environments.
 global _start

section .data
value: dq 7

section .text
_start:
        mov rax, 12
        mov rbx, 5
        mov rcx, 3
        mov rsi, 9

        cmpxchg8b [value]

        mov rax, 60         ; syscall 60: exit
        xor rdi, rdi
        syscall