text: #include "types.h"
  #include "riscv.h"
  #include "defs.h"
  #include "date.h"
  #include "param.h"
  #include "memlayout.h"
  #include "spinlock.h"
  #include "proc.h"
  #include "syscall.h"
  
  void
  print_trace(struct proc *p, char *call_name, int call_num, int retval) {
    int trace_mask = p->trace_mask;
    int pid = p->pid;
    if ((trace_mask & call_num) == call_num) {
      printf("%d: syscall %s -> %d\n", pid, call_name, retval);
    }
  }
  
  uint64
  sys_exit(void)
  {
    int n;
    if(argint(0, &n) < 0)
      return -1;
    exit(n);
    return 0;  // not reached
  }
  
  uint64
  sys_getpid(void)
  {
    return myproc()->pid;
  }
  
  uint64
  sys_fork(void)
  {
    return fork();
  }
  
  uint64
  sys_wait(void)
  {
    uint64 p;
    if(argaddr(0, &p) < 0)
      return -1;
    return wait(p);
  }
  
  uint64
  sys_sbrk(void)
  {
    int addr;
    int n;
  
    if(argint(0, &n) < 0)
      return -1;
    addr = myproc()->sz;
    if(growproc(n) < 0)
      return -1;
    return addr;
  }
  
  uint64
  sys_sleep(void)
  {
    int n;
    uint ticks0;
  
    if(argint(0, &n) < 0)
      return -1;
    acquire(&tickslock);
    ticks0 = ticks;
    while(ticks - ticks0 < n){
      if(myproc()->killed){
        release(&tickslock);
        return -1;
      }
      sleep(&ticks, &tickslock);
    }
    release(&tickslock);
    return 0;
  }
  
  uint64
  sys_kill(void)
  {
    int pid;
  
    if(argint(0, &pid) < 0)
      return -1;
    return kill(pid);
  }
  
  // return how many clock tick interrupts have occurred
  // since start.
  uint64
  sys_uptime(void)
  {
    uint xticks;
  
    acquire(&tickslock);
    xticks = ticks;
    release(&tickslock);
    return xticks;
  }
  
  uint64
  sys_trace(void)
  {
    int n;
    if (argint(0, &n) < 0) 
      return -1;
    myproc()->trace_mask = n;
    printf("sys_trace set mask complete : %d\n", n);
    return 0;
  }
  