上下文切换（中断）

以 fork系统调用 为例

中断描述符

00 00 ef 00
00 08 79 76
selector: 08
offset 00007976

调试脚本

cat gdb/intr.gdb 
set logging file gdb_output/setup.gdb.output
set logging on
set pagination off
set print repeats 0

file tools/system
target remote :1234


b fork
info b
c

#layout asm
si

x /5i $eip

info reg cs ss esp
echo --------------\n
info reg eip cs eflags esp ss

# return addr 0x68e1

######################################
# come into intr

si
echo --------------\n
info reg cs ss esp

p stack_start

x /20bx $esp

b *0x79ef
c

x /i $eip
echo --------------\n
info reg cs ss esp

######################################
# leave intr

x /20bx $esp
si

info reg cs ss esp

调试输出

cat gdb_output/setup.gdb.output 
0x0000fff0 in copy_strings (argc=0, argv=0x0 <startup_32>, page=0x0 <startup_32>, p=0, from_kmem=0) at exec.c:134
134                             if (--offset < 0) {
Breakpoint 1 at 0x68da: fork. (3 locations)
Num     Type           Disp Enb Address    What
1       breakpoint     keep y   <MULTIPLE> 
1.1                         y   0x000068da in fork at init/main.c:25
1.2                         y   0x00006a29 in fork at init/main.c:25
1.3                         y   0x00006ae0 in fork at init/main.c:25

Breakpoint 1, fork () at init/main.c:25
25      static inline _syscall0(int,fork)
0x000068df      25      static inline _syscall0(int,fork)
=> 0x68df <main+362>:   int    $0x80
   0x68e1 <main+364>:   mov    %eax,-0xc(%ebp)
   0x68e4 <main+367>:   cmpl   $0x0,-0xc(%ebp)
   0x68e8 <main+371>:   js     0x68ef <main+378>
   0x68ea <main+373>:   mov    -0xc(%ebp),%eax
cs             0xf                 15
ss             0x17                23
esp            0x29f10             0x29f10 <user_stack+4048>
--------------
eip            0x68df              0x68df <main+362>
cs             0xf                 15
eflags         0x202               [ IOPL=0 IF ]
esp            0x29f10             0x29f10 <user_stack+4048>
ss             0x17                23
0x00007979 in system_call ()
--------------
cs             0x8                 8
ss             0x10                16
esp            0x2420c             0x2420c <init_task+4076>
$1 = {a = 0x29f40 <hash_table>, b = 16}
0x2420c <init_task+4076>:       0xe1    0x68    0x00    0x00    0x0f    0x00    0x00    0x00
0x24214 <init_task+4084>:       0x02    0x02    0x00    0x00    0x10    0x9f    0x02    0x00
0x2421c <init_task+4092>:       0x17    0x00    0x00    0x00
Breakpoint 2 at 0x79ef

Breakpoint 2, 0x000079ef in ret_from_sys_call ()
=> 0x79ef <ret_from_sys_call+69>:       iret   
--------------
cs             0x8                 8
ss             0x10                16
esp            0x2420c             0x2420c <init_task+4076>
0x2420c <init_task+4076>:       0xe1    0x68    0x00    0x00    0x0f    0x00    0x00    0x00
0x24214 <init_task+4084>:       0x02    0x02    0x00    0x00    0x10    0x9f    0x02    0x00
0x2421c <init_task+4092>:       0x17    0x00    0x00    0x00
0x000068e1 in fork () at init/main.c:25
25      static inline _syscall0(int,fork)
cs             0xf                 15
ss             0x17                23
esp            0x29f10             0x29f10 <user_stack+4048>
Detaching from program: /home/mhlee/Work/dev/inf-tech/os/linux0.11_env/Linux-0.11-master/tools/system, process 1
Ending remote debugging.
[Inferior 1 (process 1) detached]