[Question] How get instruction pointer of user space ???

["liyu@WAN" <liyu@ccoss.com.cn>]

Hi everyone:

    I am implemnting one ioctl() in one character device.

    That need know instruction pointer of user space. I am on i386 
platform.
I can sure I am in process context. and enter kernel by system call way.

    As I known, in default case, each task have one kernel stack, its length
is THREAD_SIZE(2 pages),  and current_thread_info() is at its top. the
struct pt_regs is at bottom of this stack.

    so I write the code like here:

    pt_regs = ((struct pt_regs *)(THREAD_SIZE + current_thread_info()))+1;
    return pt_regs->eip;

    but it do not work! even, I get segment fault and kernel Oops at 
sometime.
   
    Also, I am sure current_thread_info() return right value of current 
user task.

    Any idea on here?

    thanks


                                                                   sailor.