pid offset into task structre

pid offset into task structre

[Fabiano Ramos]

Hi All. Some newbie question.

  I am writing some assembly code where I need to access the pid that issue
a certain syscall. In entry.S,  in the syscall stub, I wrote:

   GET_THREAD_INFO(%ebp)
   movl TI_task(%ebp), %ebp
   movl PID_OFFSET(%ebp), %ebx

 Questions are:
    1) Considering that I provided the correct value in PID_OFFSET, will
ebx contain the pid of the task that issued the syscall, at the end of the
fragment?

   2)  By taking some address arithmetic (&tsk.pid - &tsk) I got 144.  Is this
offset always the same? Is that an easy way to get it directly from
assembly code?


TIA,
Fabiano

Re: pid offset into task structre

[Vincent Hanquez]

On Thu, Oct 21, 2004 at 09:34:48PM -0200, Fabiano Ramos wrote:
> Hi All. Some newbie question.
>     1) Considering that I provided the correct value in PID_OFFSET, will
> ebx contain the pid of the task that issued the syscall, at the end of the
> fragment?

yes

>    2)  By taking some address arithmetic (&tsk.pid - &tsk) I got 144.  Is this
> offset always the same? Is that an easy way to get it directly from
> assembly code?

Generate it from arch/$ARCH/kernel/asm-offset.c with the same mecanism that
TI_task uses.

something like:

	OFFSET(TASK_pid, task_struct, pid);

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