问尝试将系统调用添加到xv6时未定义“‘proc”

EN

int clone(void(*fcn)(void*), void* arg, void* stack)
{
int i, pid;
struct proc *np;
int *myarg;
int *myret;

if((np = allocproc()) == 0)
  return -1;

np->pgdir = proc->pgdir;   //Here's where it tell's me proc is undefined
np->sz = proc->sz;
np->parent = proc;
*np->tf = *proc->tf;
np->stack = stack;

np->tf->eax = 0;

np->tf->eip = (int)fcn;

myret = stack + 4096 - 2 * sizeof(int *);
*myret = 0xFFFFFFFF;

myarg = stack + 4096 - sizeof(int *);
*myarg = (int)arg;

np->tf->esp = (int)stack +  PGSIZE - 2 * sizeof(int *);
np->tf->ebp = np->tf->esp;

np->isthread = 1;

for(i = 0; i < NOFILE; i++)
  if(proc->ofile[i])
    np->ofile[i] = filedup(proc->ofile[i]);
np->cwd = idup(proc->cwd);

safestrcpy(np->name, proc->name, sizeof(proc->name));

pid = np->pid;

acquire(&ptable.lock);
np->state = RUNNABLE;
release(&ptable.lock);

return pid;

}