本文是GCC-Inline-Assembly-HOWTO的翻译，尽量翻译正确，如有疑惑，或参看原文。

3.gcc汇编语法

GCC, the GNU C Compiler for Linux, uses AT&T/UNIX assembly syntax. Here we’ll be using AT&T syntax for assembly coding. Don’t worry if you are not familiar with AT&T syntax, I will teach you. This is quite different from Intel syntax. I shall give the major differences.

GCC使用AT&T/UNIX汇编语法。这里我们将使用AT&T汇编语法来codeing。如果你对AT&T语法不熟悉也不要担心，接下来会告诉你。GCC的AT&T汇编语法与Intel语法区别较大，主要区别有：

1. Source-Destination Ordering.

   源-目标顺序

   The direction of the operands in AT&T syntax is opposite to that of Intel. In Intel syntax the first operand is the destination, and the second operand is the source whereas in AT&T syntax the first operand is the source and the second operand is the destination. ie

   AT&T语法的操作码顺序刚好和Intel相反。在Intel语法中，它的第一个操作数是目标操作数，第二个则是源操作数。而在AT&T语法中，第一个操作数是源操作数，第二个才是目标操作数。

   *“Op-code dst src” in Intel syntax *

   “Op-code src dst” in AT&T syntax.

2. Register Naming.

   寄存器命名

   Register names are prefixed by % ie, if eax is to be used, write %eax.

   AT&T语法中，寄存器命名以%为前缀，如使用eax，写作%eax

3. Immediate Operand.

   立即操作数

   AT&T immediate operands are preceded by $. For static “C” variables also prefix a $. In Intel syntax, for hexadecimal constants an ’h’ is suffixed, instead of that, here we prefix ’0x’ to the constant. So, for hexadecimals, we first see a ’$’, then ’0x’ and finally the constants.

   AT&T立即操作数以$开头，对static“c”变量也是前置$。16进制常量，Intel语法后缀h，AT&T前缀0x。所以对于16进制数，我们会先看到$,然后是0x,最后是常量。

4. Operand Size.

   操作数大小

   In AT&T syntax the size of memory operands is determined from the last character of the op-code name. Op-code suffixes of ’b’, ’w’, and ’l’ specify byte(8-bit), word(16-bit), and long(32-bit) memory references. Intel syntax accomplishes this by prefixing memory operands (not the op-codes) with ’byte ptr’, ’word ptr’, and ’dword ptr’.

   AT&T语法中操作数大小取决于操作码最后一个字符。操作码后缀b,w,l 对应 byte(8-bit), word(16-bit), 和 long(32-bit)。Intel语法中，通过在操作数（非操作码）前缀 byte ptr, word ptr, 和 dword ptr 实现该功能。

   Thus, Intel “mov al, byte ptr foo” is “movb foo, %al” in AT&T syntax.

5. Memory Operands.

   内存操作数

   In Intel syntax the base register is enclosed in ’[’ and ’]’ where as in AT&T they change to ’(’ and ’)’. Additionally, in Intel syntax an indirect memory reference is like

   Intel语法中基址寄存器（The base register）内于[、]之间，而AT&T于(、) 之间。此外，间接内存引用（indirect memory reference）。

   section:[base + indexscale + disp] in Intel

   section:disp(base, index, scale) in AT&T.

   One point to bear in mind is that, when a constant is used for disp/scale, ’$’ shouldn’t be prefixed.

   需指出，当常量使用disp/scale，$ 无需前置。

Now we saw some of the major differences between Intel syntax and AT&T syntax. I’ve wrote only a few of them. For a complete information, refer to GNU Assembler documentations. Now we’ll look at some examples for better understanding.

以上是Intel于AT&T语法的主要区别，完整信息请参加GNU Assembler documentations。以下一些例子有助于我们更好的理解：

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