Hello, Everyone,
     "setup_arg_pages" will set "current->mm->start_stack = bprm->p;",
the code:
        ....,,
     	current->mm->start_stack = bprm->p;
	ret = expand_stack(vma, stack_base);
	if (ret)
		ret = -EFAULT;

out_unlock:
	up_write(&mm->mmap_sem);
	return ret;
        ......

In "load_elf_binary", it's double set,
        ......
	retval = setup_arg_pages(bprm, randomize_stack_top(STACK_TOP),
				 executable_stack);
	if (retval < 0)
		goto out_free_dentry;
	
	current->mm->start_stack = bprm->p;
        ......

I'm not sure if this's right. Do we have to double set start_stack?