汇编语言教程（二） 汇编器 NASM(Intel语法)& as(AT&T语法) 样例
编译器种类
汇编语言取决于处理器的指令集和体系结构。
有很多好的汇编器，例如 -
- 微软汇编器采用Intel语法(MASM)
- Borland Turbo 汇编编译器 (TASM)
- AT&T 语法的汇编编译器 - GNU gas(as) //as是作为gcc的后端来使用的
- Yet Another Assembler - YASM
- NASM是采用Intel风格语法的汇编编译器
两种语法和运行平台决定了，你可能会采用一种编译器
以下主要针对NASM和GNU的as
实验环境:
//nasm 汇编器 [root@ht6 huibian]# nasm -v //centos平台，yum install nasm安装即可 NASM version 2.10.07 compiled on Jun 9 2014 //gnu as 汇编器 [root@ht6 huibian]# as -v GNU assembler version 2.27 (x86_64-redhat-linux) using BFD version version 2.27-44.base.el7_9.1 [root@ht6 huibian]# cat /etc/redhat-release CentOS Linux release 7.9.2009 (Core) [root@ht6 huibian]# uname -a Linux ht6.node 3.10.0-1160.62.1.el7.x86_64 #1 SMP Tue Apr 5 16:57:59 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
一、编译器采用 NASM
1) nasm采用intel语法
2) nasm汇编文件后缀为 .asm
3) 段采用 section .text / section .data / section .bbs
4)注解采用 ; 形式
例子1: 寄存器采用IA-32位架构汇编代码
;Copyright (c) 1999 Konstantin Boldyshev <konst@linuxassembly.org>
;
;"hello, world" in assembly language for Linux
;
; to build an executable:
; nasm -f elf test.asm
; ld -s -o test test.o
section .text
; Export the entry point to the ELF linker or loader. The conventional
; entry point is "_start". Use "ld -e foo" to override the default.
global _start
section .data
msg db 'Hello, world!',0xa ;our dear string
len equ $ - msg ;length of our dear string
section .text
; linker puts the entry point here:
_start:
; Write the string to stdout:
mov edx,len ;message length
mov ecx,msg ;message to write
mov ebx,1 ;file descriptor (stdout)
mov eax,4 ;system call number (sys_write)
int 0x80 ;call kernel
; Exit via the kernel:
mov ebx,0 ;process' exit code
mov eax,1 ;system call number (sys_exit)
int 0x80 ;call kernel - this interrupt won't return
验证、编译test.asm
[root@ht6 huibian]# vim test.asm [root@ht6 huibian]# nasm -f elf test.asm [root@ht6 huibian]# ll total 8 -rw-r--r-- 1 root root 932 Mar 5 18:18 test.asm -rw-r--r-- 1 root root 640 Mar 5 18:18 test.o [root@ht6 huibian]# ld -s -o test test.o ld: i386 architecture of input file `test.o' is incompatible with i386:x86-64 output
这个程序编译是没有问题，因为符合语法，但是ld就会报错, 因为是x86-64平台
ld: i386 architecture of input file `test.o' is incompatible with i386:x86-64 output
例子2： 寄存器采用x86-64位架构汇编代码
; ----------------------------------------------------------------------------- ; A 64-bit Linux application that writes the first 90 Fibonacci numbers. To ; assemble and run: ; ; nasm -felf64 test1.asm && gcc test1.o && ./a.out ; ----------------------------------------------------------------------------- global main extern printf section .text main: push rbx ; we have to save this since we use it mov ecx, 90 ; ecx will countdown to 0 xor rax, rax ; rax will hold the current number xor rbx, rbx ; rbx will hold the next number inc rbx ; rbx is originally 1 print: ; We need to call printf, but we are using rax, rbx, and rcx. printf ; may destroy rax and rcx so we will save these before the call and ; restore them afterwards. push rax ; caller-save register push rcx ; caller-save register mov rdi, format ; set 1st parameter (format) mov rsi, rax ; set 2nd parameter (current_number) xor rax, rax ; because printf is varargs ; Stack is already aligned because we pushed three 8 byte registers call printf ; printf(format, current_number) pop rcx ; restore caller-save register pop rax ; restore caller-save register mov rdx, rax ; save the current number mov rax, rbx ; next number is now current add rbx, rdx ; get the new next number dec ecx ; count down jnz print ; if not done counting, do some more pop rbx ; restore rbx before returning ret format: db "%20ld", 10, 0
验证、编译 test1.asm
[root@ht6 huibian]# nasm -felf64 test1.asm [root@ht6 huibian]# ll total 12 -rw-r--r-- 1 root root 0 Mar 5 18:21 a.out -rw-r--r-- 1 root root 2021 Mar 5 18:56 test1.asm -rw-r--r-- 1 root root 832 Mar 5 18:56 test1.o -rw-r--r-- 1 root root 932 Mar 5 18:18 test.asm [root@ht6 huibian]# gcc test1.o && ./a.out
编译通过....
test1.asm 输出的结果 分析一下:
[root@ht6 huibian]# size a.out text data bss dec hex filename 1208 548 4 1760 6e0 a.out
我们看下 NASM程序的结构大概是下面的样子， 图片来自: https://cs.lmu.edu/~ray/notes/nasmtutorial/
二、汇编语法采用AT&T语法，采用GNU Gas(as) 编译器
1) gnu as采用AT&T语法
2) 段使用 .text .data .bbs
3）注解采用#形式
4) 文件后缀为.s
# ----------------------------------------------------------------------------------------
# Writes "Hello, World" to the console using only system calls. Runs on 64-bit Linux only.
# To assemble and run:
#
# gcc -c aozhejin.s && ld aozhejin.o && ./a.out
#
# or
#
# gcc -nostdlib aozhejin.s && ./a.out
# ----------------------------------------------------------------------------------------
.global _start
.text
_start:
# write(1, message, 13)
mov $1, %rax # system call 1 is write
mov $1, %rdi # file handle 1 is stdout
mov $message, %rsi # address of string to output
mov $13, %rdx # number of bytes
syscall # invoke operating system to do the write
# exit(0)
mov $60, %rax # system call 60 is exit
xor %rdi, %rdi # we want return code 0
syscall # invoke operating system to exit
message:
.ascii "this is test\n"
[root@ht5 s]# gcc -c aozhejin.s && ld aozhejin.o && ./a.out //编译通过
三、NASM 和 as 使用小结:
1、Intel和AT&T 语法是不同的
2、as是从左到右赋值，而nasm是从右到左
3、注解as是 #, 而 nasm采用;
4、标签也不同等。
所以他们之间差异还是比较大的。
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