ustack             27 kernel/exec.c    uint64 argc, sz = 0, sp, ustack[MAXARG], stackbase;
ustack            100 kernel/exec.c      ustack[argc] = sp;
ustack            102 kernel/exec.c    ustack[argc] = 0;
ustack            109 kernel/exec.c    if(copyout(pagetable, sp, (char *)ustack, (argc+1)*sizeof(uint64)) < 0)