AT&T syntax (used by default in GNU assembler) has a few differences from Intel syntax:
-
immediate values must be prefixed with a dollar sign
$ -
registers must be prefixed with a percent sign
% -
for instructions that have a source and a destination operand, their order is reversed:
instr SOURCE, DEST -
the addressing mode is in the form
displacment(base,index,scale). Only the base is required.
(The address is calculated as base + scale * index + displacment) -
whenever specifying the operand's size is required, this is done as a single-letter suffix in the instruction's name:
byte,word,dwordandqwordbecome suffixesb,w,l(long) andqrespectively.
Those differences are summarized by the table below.
| Intel syntax | AT&T syntax |
|---|---|
| mov rax, 1 | mov $1, %rax |
| mov dword [rsp], eax | movl %eax, (%rsp) |
| mov word [rbp - 8], dx | movw %dx, -8(%rbp) |
| lea rcx, qword [rsp + 2 * rax + 3] | leaq 3(%rsp,%rax,2), %rcx |