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

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

[liyu@WAN]

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.






   

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

[Gaurav Dhiman]

On 8/31/05, liyu@WAN <liyu@ccoss.com.cn> wrote:
> 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;

try doing the following, I amnot sure of it, just try it.

pt_regs = (struct pt_regs *) (((int *)(THREAD_SIZE + current)) -
(sizeof(pt_regs) + 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.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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