Control Flow in Assembly

Control flow in assembly allows conditional execution of code based on comparisons or unconditional jumps to other parts of the program.

Basic Instructions

• jmp: Unconditional jump to a label.
• je: Jump if equal (zero flag is set).
• jne: Jump if not equal (zero flag is not set).
• jg: Jump if greater (sign and zero flags are clear).
• jl: Jump if less (sign flag is set).
• loop: Decrement rcx and jump if rcx is not zero.

Example: Unconditional Jump

section .text
    global _start

_start:
    jmp skip          ; Jump to label "skip"
    mov rax, 1        ; This line is skipped
skip:
    mov rax, 2        ; Execution continues here
    

Example: Conditional Jump

section .text
    global _start

_start:
    mov rax, 10       ; Load 10 into rax
    cmp rax, 5        ; Compare rax with 5
    jg greater        ; Jump if greater
    mov rbx, 0        ; This line executes if rax <= 5
    jmp done
greater:
    mov rbx, 1        ; This line executes if rax > 5
done:
    

In this example, the program checks whether rax is greater than 5 and jumps accordingly.