系统调用是一个软中断，中断号是0x80，它是上层应用程序与Linux系统内核进行交互通信的唯一接口。
这个中断的设置在kernel/sched.c中443行函数中
1
void
sched_init(
void
)
2
{
3
int
i;
4
struct
desc_struct *
p;
5
6
if
(
sizeof
(
struct
sigaction) !=
16
)
7
panic(
"
Struct sigaction MUST be 16 bytes
"
);
8
set_tss_desc(gdt+FIRST_TSS_ENTRY,&
(init_task.task.tss));
9
set_ldt_desc(gdt+FIRST_LDT_ENTRY,&
(init_task.task.ldt));
10
p = gdt+
2
+
FIRST_TSS_ENTRY;
11
for
(i=
1
;i<NR_TASKS;i++
) {
12
task[i] =
NULL;
13
p->a=p->b=
0
;
14
p++
;
15
p->a=p->b=
0
;
16
p++
;
17
}
18
/*
Clear NT, so that we won't have troubles with that later on
*/
19
__asm__(
"
pushfl ; andl $0xffffbfff,(%esp) ; popfl
"
);
20
ltr(
0
);
21
lldt(
0
);
22
outb_p(
0x36
,
0x43
);
/*
binary, mode 3, LSB/MSB, ch 0
*/
23
outb_p(LATCH &
0xff
,
0x40
);
/*
LSB
*/
24
outb(LATCH >>
8
,
0x40
);
/*
MSB
*/
25
set_intr_gate(
0x20
,&
timer_interrupt);
26
outb(inb_p(
0x21
)&~
0x01
,
0x21
);
27
set_system_gate(
0x80
,&
system_call);
28
}
http://blog.csdn.net/yming0221/article/details/6398414
