5.MIT6.s081 lab traps2023-09-13

6.MIT6.s081 lab lazy allocation2023-09-17 7.MIT6.s081 lab cow2023-09-18

1.RISC-V assembly

1.a2, a1 store 12(f(8)+1)
2.26:   45b1   li a1,12
3.0x630
4.0x30
5.He110 World;
i = 0x726c6400;
no
6.之前a2中保存的值

2.Backtrace

关键：怎么判断用户栈超出栈底？

fp != PGROUNDDOWN(fp)

用户栈只有一页（4KB）的大小，当栈帧到达页表头时即到达栈底

void 
backtrace()
{
  printf("backtrace:\n");
  uint64 fp = r_fp();
  while (fp != PGROUNDDOWN(fp)) {
    printf("%p\n", *(uint64 *)(fp-8));
    fp = *(uint64 *)(fp - 16);
  }
  return;
}

3.Alarm

// proc.h 添加以下5个字段
struct trapframe *lastframe; // 用于保存报警前的trapframe
int alarm_interval;          // 报警间隔
uint64 handler;              // 处理函数
int interval_ticks;          // 间隔tick
int alarm_flag;              // 标记是否报警返回

// proc.c中进程启动时和释放时进行初始化和释放空间

// allocporc
// 初始化间断时间和中断返回地址
p->interval_ticks = 0;
p->alarm_flag = 0;
p->alarm_interval = 0;
p->handler = 0;
// Allocate a last trapframe page.
if((p->lastframe = (struct trapframe *)kalloc()) == 0){
release(&p->lock);
return 0;
}

//freeproc
if(p->lastframe)
    kfree((void*)p->lastframe);
p->lastframe = 0;

// sysproc.c
// 警报
uint64 
sys_sigalarm(void)
{
  int n;
  uint64 handler_pointer = 0;
  struct proc *cur_proc = myproc();
  
  if(argint(0, &n) < 0 || argaddr(1, &handler_pointer) < 0)
    return -1;
  cur_proc->alarm_interval = n;
  cur_proc->handler = handler_pointer;
  
  return 0;
}

// 返回
uint64 
sys_sigreturn(void)
{
  struct proc *cur_proc = myproc();

  if (cur_proc->alarm_flag) {
    cur_proc->interval_ticks = 0;
    *cur_proc->trapframe = *cur_proc->lastframe;
    cur_proc->alarm_flag = 0;
  }
  
  return 0;
}

// trap.c的usertrap
// 处理进程报警滴答
if(which_dev == 2) {
    p->interval_ticks ++;
    if ((p->alarm_interval != 0) && (p->alarm_flag == 0) && (p->interval_ticks == p->alarm_interval)) {
        p->alarm_flag = 1;
        *p->lastframe = *p->trapframe;
        p->trapframe->epc = p->handler;
    }
}