New Syscall Not Found (Linux Kernel 3.0.0) Where Should I Start Looking

New syscall not found (linux kernel 3.0.0) where should I start looking?

There is another set of relevant numbers that I was needed to add. The file /linux-3.0/arch/x86/kernel/syscall_table_32.c needed to be modified as well in order to properly add the syscall.

Once I added .long sys_get_slob_amnt_free and .long sys_get_slob_amnt_claimed to that file and rebuilt the kernel, I could hit my syscalls by using syscall(###) where ### is the numbering in syscall_table_32.c (not the numbering in unistd.h)

unistd_32.h and syscall_table_32.h not found

The way you add the system calls in latest kernel has been changed. Now you need to modify the following files to add a new syscall.

      arch/x86/syscalls/syscall_32.tbl >> for 32-bit 
arch/x86/syscalls/syscall_64.tbl >> for 64-bit

An example of adding sys_finit_module:

vim /arch/x86/syscalls/syscall_32.tbl

       347  i386    process_vm_readv    sys_process_vm_readv          compat_sys_process_vm_readv
348 i386 process_vm_writev sys_process_vm_writev compat_sys_process_vm_writev
349 i386 kcmp sys_kcmp
**350 i386 finit_module sys_finit_module**

vim include/linux/syscalls.h

     asmlinkage long sys_finit_module(int fd, const char __user *uargs);

Error syscall : Function not implemented

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
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.

Writing a new system call

You should use SYSCALL_DEFINE* to define syscall (I think, this step you did wrong), then add your syscall into sys_call_table, which is architecture-dependent (arch/arm/kernel/calls.S for arm).

Change your sys_defclose to look like this:

SYSCALL_DEFINE1(defclose, pid_t, pid)
struct task_struct *result = NULL;

result = get_task_by_pid(pid);

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