在openwrt-widora环境下用汇编实现hello world, 用syscall来调用print和exit,其特点就是编译出来的可执行文件比用C编译出的小了很多。
1. 代码： asmhello.S
#include <asm/regdef.h>
#include <asm/unistd.h>
.data
msg: .ascii "Hello World!\n"
length: .word . - msg
.text
.globl main
main:
move a0,$0
la a1,msg
lw a2,length
li v0,__NR_write
syscall
li v0,__NR_exit
syscall
2. 编译：
./openwrt-gcc -c -fno-builtin asmhello.S
3. 链接：
./openwrt-ld -e main -static asmhello.o -o hello
4. 剥离符号:
./openwrt-strip hello -o hello
(openwrt-xx等是相应的openwrt环境下的交叉编译工具）
5. 查看编译出来的文件:
./openwrt-objdump -d /tmp/hello
004000b0 <.text>:
4000b0: 00002021 move a0,zero
4000b4: 3c050041 lui a1,0x41
4000b8: 24a500e0 addiu a1,a1,224
4000bc: 3c060041 lui a2,0x41
4000c0: 8cc600f0 lw a2,240(a2)
4000c4: 24020fa4 li v0,4004
4000c8: 0000000c syscall
4000cc: 24020fa1 li v0,4001
4000d0: 0000000c syscall
./openwrt-objdump -s /tmp/hello
/tmp/hello: file format elf32-tradlittlemips
Contents of section .reginfo:
400094 74000000 00000000 00000000 00000000 t...............
4000a4 00000000 f0804100 ......A.
Contents of section .text:
4000b0 21200000 4100053c e000a524 4100063c ! ..A..<...$A..<
4000c0 f000c68c a40f0224 0c000000 a10f0224 .......$.......$
4000d0 0c000000 00000000 00000000 00000000 ................
Contents of section .data:
4100e0 48656c6c 6f205769 646f7261 210a0000 Hello World!...
4100f0 10000000 00000000 00000000 00000000 ................
参考资料:
http://www.tldp.org/HOWTO/Assembly-HOWTO/mips.html
《程序员的自我修养–链接，装载库》（俞甲子等）
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