# Assembly


* Instruction Set Architecture

** representation

| LLVM       | Intel             | Meaning       |
| *COMMONDq* | command qword ptr | qword (64bit) |

** divl
| Opcode        | Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description                                                                                |
| F6 /6         | DIV r/m8    | M     | Valid       | Valid           | Unsigned divide AX by r/m8, with result stored in AL := Quotient, AH := Remainder.         |
| REX + F6 /6   | DIV r/m81   | M     | Valid       | N.E.            | Unsigned divide AX by r/m8, with result stored in AL := Quotient, AH := Remainder.         |
| F7 /6         | DIV r/m16   | M     | Valid       | Valid           | Unsigned divide DX:AX by r/m16, with result stored in AX := Quotient, DX := Remainder.     |
| F7 /6         | DIV r/m32   | M     | Valid       | Valid           | Unsigned divide EDX:EAX by r/m32, with result stored in EAX := Quotient, EDX := Remainder. |
| REX.W + F7 /6 | DIV r/m64   | M     | Valid       | N.E.            | Unsigned divide RDX:RAX by r/m64, with result stored in RAX := Quotient, RDX := Remainder. |


- dividend:  ~[%edx (high 32 bit), %eax (low 32 bit)]~
- divisor:   ~operand~
- remainder: ~[%edx (high 32 bit), %eax (low 32 bit)]~
- quotient: ~rax~


* AT&T -- Intel

** syntax
|                  | Intel                                     | AT&T                            |
| Comments         | ;                                         | //                              |
| Instructions     | Untagged add                              | Tagged with operand sizes: addq |
| Registers        | eax, ebx, etc.                            | %eax,%ebx, etc.                 |
| Immediates       | 0x100                                     | $0x100                          |
| Indirect         | [eax]                                     | (%eax)                          |
| General indirect | [base + reg + reg * scale + displacement] | displacement(reg, reg, scale)   |

*** prefix

| Intex Syntax     | AT&T Syntax        |
| mov     eax,1    | movl    $1,%eax    |
| mov     ebx,0ffh | movl    $0xff,%ebx |
| int     80h      | int     $0x80      |

*** direction

| Intex Syntax        | AT&T Syntax          |
| instr   dest,source | instr   source,dest  |
| mov     eax,[ebx+3] | movl    3(%ebx),%eax |


** gdb
#+begin_src gdb
set disassembly-flavor att/intel
#+end_src

** objdump
#+begin_src
objdump -M intel
#+end_src