asm_x86_无条件跳转

汇编语言程序设计-学习
第6章：控制执行流程
目录：
无条件分支：
<1>.跳转
短跳：128byte之内
长跳：分段内存模式，跳转到另一个段
近跳：其他
<2>.调用
<3>.中断
条件分支：(EFLAGS-register)
carry--进位(CF):0bit,主要用于无符号数小于0，或是大于数字范围。
overflow--溢出（OF）：11bit，主要用于有符号位，超出范围。
parity--奇偶校验（PF）：2bit
sign--符号（SF）：7bit
zero--零（ZF）：6bit

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一.无条跳转：


1.跳转：
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<1>//编辑汇编源文件
root@ubuntu-core:/home/asm/6_1# cat test.s
# jump test.s -An example of the jmp instruction.


.section .text
.globl _start
_start:
nop
movl $1 ,%eax
jmp overhere
movl $10,%ebx
int $0x80
overhere:
movl $20,%ebx
int $0x80
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<2>.//编译、链接、运行
root@ubuntu-core:/home/asm/6_1# 
root@ubuntu-core:/home/asm/6_1# as -o test.o test.s
root@ubuntu-core:/home/asm/6_1# ld -o test test.o
root@ubuntu-core:/home/asm/6_1# ./test
root@ubuntu-core:/home/asm/6_1# echo $?
20
root@ubuntu-core:/home/asm/6_1# 
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<3>.//使用可执行文件，反汇编，监视程序中实际使用的内存位置
root@ubuntu-core:/home/asm/6_1# objdump -D test


test:     file format elf64-x86-64  //我的系统时64位的.


Disassembly of section .text:


0000000000400078 <_start>:
  400078: 90                   nop
  400079: b8 01 00 00 00       mov    $0x1,%eax
  40007e: eb 07                 jmp    400087 <overhere>
  400080: bb 0a 00 00 00       mov    $0xa,%ebx
  400085: cd 80                 int    $0x80


0000000000400087 <overhere>:
  400087: bb 14 00 00 00       mov    $0x14,%ebx
  40008c: cd 80                 int    $0x80
root@ubuntu-core:/home/asm/6_1# 


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<4>.//gdb单步调试，查看程序执行流程
root@ubuntu-core:/home/asm/6_1# as -gstabs  -o test.o test.s  //-gstabs
调试参数：调试器对代码进行汇编
root@ubuntu-core:/home/asm/6_1# ld -o test test.o
root@ubuntu-core:/home/asm/6_1# gdb -q test //-q 去除一些开始信息
Reading symbols from /home/asm/6_1/test...done.
(gdb) break *_start+1 //设置断点
Breakpoint 1 at 0x400079: file test.s, line 10.
(gdb) run //开始运行
Starting program: /home/asm/6_1/test 
warning: no loadable sections found in added symbol-file system-supplied DSO 
at 0x7ffff7ffd000


Breakpoint 1, _start () at test.s:10
10 movl $1 ,%eax
(gdb) info register //查看程序运行中，各个寄存器的值
rax            0x0 0
rbx            0x0 0
rcx            0x0 0
rdx            0x0 0
rsi            0x0 0
rdi            0x0 0
rbp            0x0 0x0
rsp            0x7fffffffe010 0x7fffffffe010
r8             0x0 0
r9             0x0 0
r10            0x0 0
r11            0x200 512
r12            0x0 0
r13            0x0 0
r14            0x0 0
r15            0x0 0
rip            0x400079 0x400079 <_start+1>
eflags         0x202 [ IF ]
cs             0x33 51
ss             0x2b 43
ds             0x0 0
es             0x0 0
fs             0x0 0
gs             0x0 0
(gdb) print/x $rip //十六进制打印单个寄存器
$1 = 0x400079
(gdb) s //step，单步运行
11 jmp overhere
(gdb) s
overhere () at test.s:15
15 movl $20,%ebx
(gdb) print/x $rip
$2 = 0x400087
(gdb) s
16 int $0x80
(gdb) print/x $rip
$3 = 0x40008c
(gdb) s
[Inferior 1 (process 50888) exited with code 024]
(gdb) 




++++++++++++++++++++++++++++++++++++++++++++++++++++++
2.调用：


root@ubuntu-core:/home/asm/6_1# cat calltest.s 
#calltest.s -An example of using the CALL instruction


#.code32 //64位汇编与32位汇编不大一样，限定为32位汇编
.section .data
output:
.asciz "This is section %d\n"
.section .text
.globl main
main:
pushl $1
pushl $output
call printf
add $8,%esp
call overhere
pushl $3
pushl $output
call printf
add $8,%esp
pushl $0
call exit


overhere:
pushl %ebp
movl %esp,%ebp
pushl $2
pushl $output
call printf
add $8,%esp
movl %ebp,%esp
popl %ebp
ret
root@ubuntu-core:/home/asm/6_1# gcc -m32 calltest.s -o test  //由于我的机子是
X64的
root@ubuntu-core:/home/asm/6_1# ./test
This is section 1
This is section 2
This is section 3
root@ubuntu-core:/home/asm/6_1# 


++++++++++++++++++++++++++++++++++++++++++++++++++++++
3.中断
软中断：linux中系统调用也是软件中断
硬中断：硬件产生。
linux：0x80


======================================================
二.条件跳转
使用奇偶校验标志为例：
root@ubuntu-core:/home/asm/6_1# cat paritytest.s 


#paritytest.s -An example of testing the parity flag


.section .text
.globl _start
_start:
movl $1,%eax
movl $4,%ebx
subl $3,%ebx
jp overhere
int $0x80
overhere:
movl $100,%ebx
int $0x80


root@ubuntu-core:/home/asm/6_1# as paritytest.s -o test.o
root@ubuntu-core:/home/asm/6_1# ld test.o -o test
root@ubuntu-core:/home/asm/6_1# ./test
root@ubuntu-core:/home/asm/6_1# echo $?
1
root@ubuntu-core:/home/asm/6_1# vim paritytest.s 
root@ubuntu-core:/home/asm/6_1# as paritytest.s -o test.o
root@ubuntu-core:/home/asm/6_1# ld test.o -o test
root@ubuntu-core:/home/asm/6_1# ./test
root@ubuntu-core:/home/asm/6_1# echo $?
100
root@ubuntu-core:/home/asm/6_1#