1 _system_call:
2 cmpl $nr_system_calls-1,%eax
3 ja bad_sys_call
4 push %ds
5 push %es
6 push %fs
7 pushl %edx
8 pushl %ecx # push %ebx,%ecx,%edx as parameters
9 pushl %ebx # to the system call
10 movl $0x10,%edx # set up ds,es to kernel space
11 mov %dx,%ds
12 mov %dx,%es
13 movl $0x17,%edx # fs points to local data space
14 mov %dx,%fs
15 call _sys_call_table(,%eax,4)
16 pushl %eax
17 movl _current,%eax
18 cmpl $0,state(%eax) # state
19 jne reschedule
20 cmpl $0,counter(%eax) # counter
21 je reschedule
22  ret_from_sys_call:
23 movl _current,%eax # task[0] cannot have signals
24 cmpl _task,%eax
25 je 3f
26 cmpw $0x0f,CS(%esp) # was old code segment supervisor ?
27 jne 3f
28 cmpw $0x17,OLDSS(%esp) # was stack segment = 0x17 ?
29 jne 3f
30 movl signal(%eax),%ebx
31 movl blocked(%eax),%ecx
32 notl %ecx
33 andl %ebx,%ecx
34 bsfl %ecx,%ecx
35 je 3f
36 btrl %ecx,%ebx
37 movl %ebx,signal(%eax)
38 incl %ecx
39 pushl %ecx
40 call _do_signal
41 popl %eax
42  3: popl %eax
43 popl %ebx
44 popl %ecx
45 popl %edx
46 pop %fs
47 pop %es
48 pop %ds
49 iret

1 void schedule(void)
2 {
3 int i,next,c;
4 struct task_struct ** p;
5
6 /* check alarm, wake up any interruptible tasks that have got a signal */
7
8 for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
9 if (*p) {
10 if ((*p)->alarm && (*p)->alarm < jiffies) {
11 (*p)->signal |= (1<<(SIGALRM-1));
12 (*p)->alarm = 0;
13 }
14 if (((*p)->signal & ~(_BLOCKABLE & (*p)->blocked)) &&
15 (*p)->state==TASK_INTERRUPTIBLE)
16 (*p)->state=TASK_RUNNING;
17 }
18
19 /* this is the scheduler proper: */
20
21 while (1) {
22 c = -1;
23 next = 0;
24 i = NR_TASKS;
25 p = &task[NR_TASKS];
26 while (--i) {
27 if (!*--p)
28 continue;
29 if ((*p)->state == TASK_RUNNING && (*p)->counter > c)
30 c = (*p)->counter, next = i;
31 }
32 if (c) break;
33 for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
34 if (*p)
35 (*p)->counter = ((*p)->counter >> 1) +
36 (*p)->priority;
37 }
38 switch_to(next);
39 }

1 #define switch_to(n) {\
2 struct {long a,b;} __tmp; \
3 __asm__("cmpl %%ecx,_current\n\t" \
4 "je 1f\n\t" \
5 "movw %%dx,%1\n\t" \
6 "xchgl %%ecx,_current\n\t" \
7 "ljmp %0\n\t" \
8 "cmpl %%ecx,_last_task_used_math\n\t" \
9 "jne 1f\n\t" \
10 "clts\n" \
11 "1:" \
12 ::"m" (*&__tmp.a),"m" (*&__tmp.b), \
13 "d" (_TSS(n)),"c" ((long) task[n])); \
14 }