Why system call is returning -1 ??????

["Harshal Sarode" <sarodeharshal@xxxxxxxxx>]

hi,

   Any one  plz help me....

   I want to write a system call into a kernel.

   i followed all steps of writing a system call to kernel.

   i did.....

   1) updated ./linux/include/asm/unistd.h

   2)updated ./linux/arch/386/kernel/syscall_table.S

  3) then wrote my own  system call code in ./linux/kernel/sys.c file

 

asmlinkage long sys_getjiffies( void )       

{
  return (long)get_jiffies_64();       // read jiffies with the get_jiffies_64 function.
}
 

//The Linux kernel maintains a global variable called jiffies, which represents the number of timer ticks since the machine started

 

 4) after compiling kernel , when i tried to call that system call , it returned me -1.

 

Following code i used to call system call created above.

#include <linux/unistd.h>
#include <sys/syscall.h>

#define __NR_getjiffies 320

int main()
{
  long jiffies;

  jiffies = syscall( __NR_getjiffies );

  printf( "Current jiffies is %lx\n", jiffies );

  return 0;
}
 

Plz help me....... why system call  is returning negative value.

 

Thanks in advance.