CDQE - x86-64 instruction reference

cdqeSign-extend eax into rax 
Sign-extends eax into rax, filling the upper 32 bits with copies of eax's sign bit so 32-bit signed values work in 64-bit arithmetic.
x86-64 and later
Intel's reference: CBW/CWDE/CDQE 
CFPFAFZFSFDFOF –––––––
Changes no flag
Forms  cdqe  
It takes no operands and changes no other register or flags. For example, eax = 0xffffffff becomes rax = -1. NASM can assemble movsxd rax, eax to the same instruction.
 global _start

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

        cdqe

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