Error syscall : Function not implemented - operating-system

Question

I'm trying to add new (dummy) system call to linux kernel.
1) I added the system call code under linux-source/kernel/myfile.c and updated the Makefile accordingly.
2) Updated syscall.h, unistd.h and entry.S files to reflect the new system call (pedagogictime(int flag,struct timeval *time))
Then compiled the kernel and installed and rebooted the image.
When I run: cat /proc/kallsyms | grep "pedag", this is the output I'm getting
0000000000000000 T sys_pedagogictime
0000000000000000 d event_exit__pedagogictime
0000000000000000 d event_enter__pedagogictime
0000000000000000 d __syscall_meta_pedagogictime
0000000000000000 d types_pedagogictime
0000000000000000 d args__pedagogictime
0000000000000000 t trace_init_flags_enter__pedagogictime
0000000000000000 t trace_init_flags_exit__pedagogictime
0000000000000000 t __event_exit__pedagogictime
0000000000000000 t __event_enter__pedagogictime
0000000000000000 t __p_syscall_meta__pedagogictime
0000000000000000 t __initcall_trace_init_flags_exit__pedagogictimeearly
0000000000000000 t __initcall_trace_init_flags_enter__pedagogictimeearly
which means the system call is registered correctly.
In my user space program, I'm writing:
#define __NR_pedagogictime 1326 //1326 is my system call number
struct timeval *now = (struct timeval *)malloc(sizeof(struct timeval));
long ret = syscall(__NR_pedagogictime,0,now);
if(ret)
perror("syscall ");
But I'm getting the error:
"syscall : Function not implemented"
I would really appreciate any help about this. Thanks.
Edit:
Btw, the assembly code for the syscall() looks like this (if it helps):
movl $6, %esi
movl $1326, %edi
movl $0, %eax
call syscall
cltq

Answer 1

You've chosen the wrong syscall number. Take a look at how the kernel checks the syscall number limits here. For example (x86, 32bit):
496 ENTRY(system_call)
497 RING0_INT_FRAME # can't unwind into user space anyway
498 pushl_cfi %eax # save orig_eax
499 SAVE_ALL
500 GET_THREAD_INFO(%ebp)
501 # system call tracing in operation / emulation
502 testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)
503 jnz syscall_trace_entry
504 cmpl $(nr_syscalls), %eax
505 jae syscall_badsys
506 syscall_call:
507 call *sys_call_table(,%eax,4)
508 movl %eax,PT_EAX(%esp) # store the return value
So, you can see that this code compares %eax (syscall number) and nr_syscalls (sys_call_table size). Above or equal leads to syscall_badsys.
You'll need to modify the arch/x86/include/asm/unistd_32.h header too.