hi,
intel processors runs in 4 privilage mode,kernel runs
in highest privilage mode
,You are in user mode so the segmenation hardware
loaded the data and code segment descriptor
with user data and user code segment,and you are
trying to access the
kernel data structure from user space which is
something you never reach,
So for accessing the kernel data struture yr data
segment must be set with
kernel data segment,but then yr code segment is set to
user code segment,
so processor will again generate exceptions as your
user space code trying to access kernel space code,
so better way is to do it in kernel modules which is
something like dynamically loaded
extensions to kernel code,
where you can directly access the member of
task_struct structure,
but genrally the work should get done by using the
exported funtions
by kernel u get them in /proc/ksyms,
more information about kernel programming you will get
on web,
and ofcourse the bible for every kernel programmer
"linux device drivers"
by rubini is always there.
Prasanna
--- Alexander Nyberg <alexn@telia.com> wrote:
> > Hi all,
> > I'm trying to develop a C program that access to
> > process descriptor information but I have had some
> > problem with libraries.
> > In particular, I've developed a program like this:
> >
> > #include <linux/sched.h>
> >
> > int main(void){
> > pid_t pid;
> > ....
> > task_struct process = find_task_by_pid(pid);
> > ...
> > }
> >
> > but the compiler can't find get_task_by_pid
> function,
> > while this is a function declared in
> > include/linux/sched.h.
> > What's wrong?
>
> The problem is that the function get_task_by_pid()
> lives in the kernel,
> and you cannot call arbitrary functions in the
> kernel (think of what
> that would mean to security and isolation). The
> functions you can access
> from user space are system calls.
>
> > Are there other methods to access process
> descriptor
> > pointer?
>
> If you need more than what is already available from
> the task_struct you
> would preferably add another system call to your
> linux (there are other
> ways too).
>
> Maybe something like:
> sys_get_task_struct(pid_t pid, struct task_struct
> __user *to)
> {
> task_struct *task = find_task_by_pid(pid);
> copy_to_user(to, task, sizeof(struct task_struct));
> }
>
> Alex
>
>
> --
> Kernelnewbies: Help each other learn about the Linux
> kernel.
> Archive:
> http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
>
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Kernelnewbies: Help each other learn about the Linux kernel.
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