Memory Addressing Modes

Memory addressing modes define how instructions access data stored in memory or registers. Understanding these modes is crucial for efficient assembly programming.

Common Addressing Modes

• Immediate Addressing: The operand is a constant value.
• Register Addressing: The operand is in a register.
• Direct Addressing: The operand's memory address is specified.
• Indirect Addressing: The memory address is stored in a register.
• Indexed Addressing: A base address plus an index is used to calculate the effective address.

Examples

1. Immediate Addressing

mov rax, 5       ; Load the immediate value 5 into rax
    

2. Register Addressing

mov rax, rbx     ; Copy the value of rbx into rax
    

3. Direct Addressing

section .data
    num db 10       ; Define a byte in memory

section .text
    mov al, [num]   ; Load the value at memory address 'num' into AL
    

4. Indirect Addressing

section .bss
    buffer resb 4    ; Reserve 4 bytes in memory

section .text
    mov rsi, buffer  ; Load the address of 'buffer' into RSI
    mov byte [rsi], 42 ; Store 42 at the address in RSI
    

5. Indexed Addressing

section .data
    array db 1, 2, 3, 4  ; Define an array

section .text
    mov rsi, array       ; Load the base address of 'array' into RSI
    mov al, [rsi+2]      ; Load the third element of the array into AL
    

Indexed addressing is useful for working with arrays and data structures.