A loop is a block of statements that are repeatedly executed until a condition is satisfied. The assembly language uses JMP instruction to implement loops. However, the processor set can use the LOOP instruction to implement loops conveniently.
loop in assembly language
Loop is used to repeatedly run any code block or group of instructions.
loop instruction work in assembly language
The LOOP instruction assumes that the ECX register contains the loop count. When the loop instruction is executed, the ECX register is decremented and the control jumps to the target label, until the ECX register value, i.e., the counter reaches the value zero.
Assembly Loop Syntax
The processor instruction set includes a set of loop instructions to implement recursion. The JMP instruction can be used to implement a loop. Where, label is the target label that identifies the target instruction as in the jump instructions.
Syntax LOOP labelFor example
MOV CL, 10
L1:
-LOOP-BODY-
DEC CL
JNZ L1Assembly Loop Exampal
The following program prints the number 1 to 8 on the screen −
section .text
global _start ;must be declared for using gcc
_start: ;tell linker entry point
mov ecx,9
mov eax, '1'
l1:
mov [num], eax
mov eax, 4
mov ebx, 1
push ecx
mov ecx, num
mov edx, 1
int 0x80
mov eax, [num]
sub eax, '0'
inc eax
add eax, '0'
pop ecx
loop l1
mov eax,1 ;system call number (sys_exit)
int 0x80 ;call kernel
section .bss
num resb 1 When the above code is compiled and executed, it produces the following result −
12345678:
