stosq
Store quadword to string
Stores rax at [rdi], then advances rdi by 8, backward when DF is set.
x86-64 and later
CFPFAFZFSFDFOF –––––––
- Changes no flag
- Reads DF
Forms
stosq
The q suffix selects an element of 8 bytes. After each element, the instruction increases rdi by 8 when DF = 0, or decreases rdi by 8 when DF = 1. In 64-bit mode the default addresses use rdi. The a32 address-size prefix instead uses edi; 16-bit string addressing is unavailable.
rep repeats until the counter reaches zero. The counter is rcx by default or ecx with a32. If it starts at zero, a repeated instruction accesses no element. The data width is independent of this address and counter width.
global _start
section .data
source: db 1, 2, 3, 4, 5, 6, 7, 8
destination: times 8 db 0
section .text
_start:
cld ; count upwards
mov rsi, source
mov rdi, destination
mov rax, 7
stosq ; writes rax to [rdi]
mov rax, 60 ; syscall 60: exit
xor rdi, rdi
syscall