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_wait(void)
  {
    return wait();
  }
  
  int
  sys_exitS(void)
  {
      int status;
  
      if(argint(0, &status) < 0)
          return -1;
      exitS(status);
      return 0;
  }
  
  int
  sys_waitS(void)
  {
      int *status;
  
      if(argptr(0, (char**)&status, sizeof(int*) < 0))
          return -1;
      return waitS(status);
  }
  
  int
  sys_waitpid(void)
  {
      int pid;
      int *status;
      int options;
  
      if(argint(0, &pid) < 0)
          return -1;
  
      if(argptr(1, (char**)&status, sizeof(int*) < 0))
          return -1;
  
      if(argint(2, &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;
  }
  
  int
  sys_hello(void) {
      hello();
      return 0;
  }
  