Star on github
AI Chat

movabs

Move with explicit immediate or absolute offset

Copies a full-width immediate into a register, or transfers accumulator data using an absolute memory offset.

8086 and later

Intel's reference: MOV

CFPFAFZFSFDFOF –––––––
  • Changes no flag

Forms

Operands

reg
A general-purpose register matching the operation’s size, for example al, ax, eax or rax. The byte registers ah, bh, ch and dh cannot be used with a REX prefix, which is required by spl, bpl, sil, dil and r8–r15.
imm
An immediate value encoded in the instruction, written as a number, character or label. Its encoded width and any sign extension depend on the instruction; arithmetic immediates may be sign-extended, while shift counts are used without sign extension.
acc
The accumulator matching the operation’s size: al, ax, eax or rax. A shorter encoding may be available.
moffs
An absolute memory address with no base or index register, such as [label], used by mov to transfer data to or from the accumulator.

For example, movabs rax, 1 keeps the full 64-bit immediate and is 10 bytes, whereas NASM can shorten mov rax, 1 to a 32-bit register write. Both mov rax, 0x123456789abcdef0 and movabs rax, 0x123456789abcdef0 load the complete constant.

The byte, word and doubleword register-immediate forms use their respective immediate widths. The memory forms transfer data between an absolute address and al, ax, eax or rax. Use an explicit 64-bit memory offset in 64-bit code, for example movabs rax, [abs qword 0x1000]. Their lengths depend on the address and data widths. The 10-byte length applies to movabs reg64, imm64.

global _start

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

        movabs rax, 5

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