Assembly Syntax Intel & AT&T
25 Mar 2014This post is just a little cheat sheet for myself on Intel & AT&T syntax.
A useful table mapping some simple instructions between the two syntaxes linked through from the GCC-Inline-Assembly-HOWTO:
| Intel Code | AT&T Code |
|---|---|
mov eax,1 |
movl $1,%eax |
mov ebx,0ffh |
movl $0xff,%ebx |
int 80h |
int $0x80 |
mov ebx, eax |
movl %eax, %ebx |
mov eax,[ecx] |
movl (%ecx),%eax |
mov eax,[ebx+3] |
movl 3(%ebx),%eax |
mov eax,[ebx+20h] |
movl 0x20(%ebx),%eax |
add eax,[ebx+ecx*2h] |
addl (%ebx,%ecx,0x2),%eax |
lea eax,[ebx+ecx] |
leal (%ebx,%ecx),%eax |
sub eax,[ebx+ecx*4h-20h] |
subl -0x20(%ebx,%ecx,0x4),%eax |
Some important points to note:
- Source and destinations are flipped in opcodes.
- Intel is dest, src
- AT&T is src, dest
- AT&T decorates registers and immediates
- Registers are prefixed with a “%”
- Immediates are prefixed with a “$”. This applies to variables being passed in from C (when you’re inline).
- Intel decorates memory operands to denote the operand’s size, AT&T uses different mnemonics to accomplish the same.
- Intel syntax to dereference a memory location is “[ ]”. AT&T uses “( )”.