text: #include "types.h"
  #include "x86.h"
  #include "defs.h"
  #include "date.h"
  #include "param.h"
  #include "memlayout.h"
  #include "mmu.h"
  #include "proc.h"
  
  int
  sys_fork(void)
  {
    return fork();
  }
  
  int
  sys_exit(void)
  {
    exit();
    return 0;  // not reached
  }
  
  int
  sys_exitS(void)
  {
     int status;
     if(argint(0,&status) < 0)
       return -1;
     exitS(status);
     return 0;
  }
  
  int
  sys_wait(void)
  {
    return wait();
  }
  
  int
  sys_waitS(void)
  {
    int *ptr;
    if(argptr(0,(char**)&ptr, sizeof(int*)) < 0)
      return -1;
    return waitS(ptr);
  }
  
  int
  sys_waitPID(void)
  {
    int pid;
    if(argint(0,&pid) < 0)
      return -1;
    int *status;
    if(argptr(1,(char**)&status, sizeof(int*)) < 0)
      return -1;
    int options;
    if(argint(0,&options) < 0)
      return -1;
    return waitPID(pid, status, options);
  }
  
  int
  sys_kill(void)
  {
    int pid;
  
    if(argint(0, &pid) < 0)
      return -1;
    return kill(pid);
  }
  
  int
  sys_getpid(void)
  {
    return myproc()->pid;
  }
  
  int
  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;
  }
  
  int
  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;
  }
  
  // return how many clock tick interrupts have occurred
  // since start.
  int
  sys_uptime(void)
  {
    uint xticks;
  
    acquire(&tickslock);
    xticks = ticks;
    release(&tickslock);
    return xticks;
  }
  