creating own syscall on 2.6.37.3 and getting error on compilaton...

[Filipe Rinaldi]

On 22 October 2012 01:10,  <rgonzale at darkterminal.net> wrote:
> Ah the kernel/sched directory was added in 3.3.  I'm using 2.6.37.3.
>
>
> -Tristan
> On Sun, Oct 21, 2012 at 11:14:32PM +0100, Filipe Rinaldi wrote:
>> On 21 October 2012 21:28,  <rgonzale at darkterminal.net> wrote:
>> > I'm trying to implement my own system call on Linux kernel 2.6.37.3 using this guide.
>> >
>> > http://enzam.wordpress.com/2011/03/2...nel-ubuntu-os/
>> >
>> > Here's the code that I have for kernel/mysystemcalls.c
>> > It just takes an int for an argument and then spits out the PIDs for the process that is running on that CPU.
>> > Code:
>> >
>> > #include<linux/linkage.h>
>> > #include<linux/cpumask.h>
>> > asmlinkage long sys_current_pid(int i)  {
>> >         struct rq *rq;
>> >         int num_cpu;
>> >         num_cpu = num_online_cpus();
>> >         if(i <= 0 || i > num_cpu)
>> >                 return -1;
>> >
>> >         rq = cpu_rq(i);
>> >         if(rq->curr != NULL)
>> >                 return rq->curr->pid;
>> >         else
>> >                 return -1;
>> > }
>> >
>> > But on kernel compilation I get this.
>> > Code:
>> >
>> > kernel/mysystemcalls.c: In function 'sys_current_pid':
>> > kernel/mysystemcalls.c:12: error: implicit declaration of function 'cpu_rq'
>> > kernel/mysystemcalls.c:12: warning: assignment makes pointer from integer without a cast
>> > kernel/mysystemcalls.c:13: error: dereferencing pointer to incomplete type
>> > kernel/mysystemcalls.c:14: error: dereferencing pointer to incomplete type
>> > make[1]: *** [kernel/mysystemcalls.o] Error 1
>> > make[1]: *** Waiting for unfinished jobs....
>> >
>> > The definition for cpu_rq() is in kernel/sched.c.
>>
>> sched.c contains the implementation, the definition is in
>> sched/sched.h, you should #include that header.
>>
>> > Here's the pertinent piece of Makefile in kernel/Makefile
>> > Code:
>> >
>> > #
>> > # Makefile for the linux kernel.
>> > #
>> >
>> > obj-y     = sched.o fork.o exec_domain.o panic.o printk.o \
>> >                                 cpu.o exit.o itimer.o time.o softirq.o resource.o \
>> >                                 sysctl.o sysctl_binary.o capability.o ptrace.o timer.o user.o \
>> >                                 signal.o sys.o kmod.o workqueue.o pid.o \
>> >                                 rcupdate.o extable.o params.o posix-timers.o \
>> >                                 kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
>> >                                 hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
>> >                                 notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o \
>> >                                 async.o range.o jump_label.o
>> >                                 obj-y += mysystemcalls.o
>> >
>> >                                 I would think that since sched.o(the first c file that gets compiled) has the definition for the cpu_rq() then mysystemcalls.c should be able to see that function. What am I missing?
>> >
>>
>> You don't have a *link* error. It is not that the linker can't find cpu_rq().
>> It is the compiler that does not understand the cpu_rq() definition.
>> Try to include the header.
>>
>> Cheers,
>> -Filipe


Humm, on 2.6.37 this is a private macro in sched.c.

I suppose you could use "current->pid".
"current" is a macro that returns the current task's structure:
http://lxr.linux.no/linux+v2.6.37.3/arch/x86/include/asm/current.h#L17

-Filipe