How to pass parameters to Linux system call?

I'm a college student studying OS.

I'm trying to add my own system call in Linux kernel, and something is going wrong.

My environment is stated below:

• Linux Kernel v.4.19.1
• 64-bit Ubuntu LTS 18.04.1 with Intel Core i5-4210M CPU on Oracle VirtualBox 5.2.18
• 64-bit Windows 10 Home 1803 as a host machine

Since I'm working on x86_64 machine, I started with arch/x86/entry/syscalls/syscall_64.tbl. In Linux kernel v.4.19.1, the last entry is

334     common     rseq             __x64_sys_rseq

so I added those three lines below it.

335     common     my_syscall_0     sys_my_syscall_0
336     common     my_syscall_1     sys_my_syscall_1
337     common     my_syscall_2     sys_my_syscall_2

Second, I added prototypes of functions in include/linux/syscalls.h.

asmlinkage int sys_my_syscall_0(void);
asmlinkage int sys_my_syscall_1(int);
asmlinkage int sys_my_syscall_2(int, int);

Third, I created a new file kernel/my_syscall.c and added implementations of functions.

asmlinkage int sys_my_syscall_0(void)
{
    printk("my_syscall_0\n");
    return 0;
}

asmlinkage int sys_my_syscall_1(int a)
{
    printk("my_syscall_1 : %d\n", a);
    return 0;
}

asmlinkage int sys_my_syscall_0(int a, int b)
{
    printk("my_syscall_2 : %d, %d\n", a, b);
    return b;
}

Then, I added my_syscall.o in kernel/Makefile to compile kernel/my_syscall.c as well.

obj-y = fork.o exec_domain.o panic.o \
        cpu.o exit.o softirq.o resource.o \
        sysctl.o sysctl_binary.o capability.o ptrace.o user.o \
        signal.o sys.o umh.o workqueue.o pid.o task_work.o \
        extable.o params.o \
        kthread.o sys_ni.o nsproxy.o \
        notifier.o ksysfs.o cred.o reboot.o \
        async.o range.o smpboot.o ucount.o \
        my_syscall.o

After compilation with make-kpkg and dpkg command, I made a test program.

#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
int main()
{
    printf("1 : %d\n", syscall(335));
    printf("2 : %d\n", syscall(336, 1));
    printf("3 : %d\n", syscall(337, 2, 3));
    return 0;
}

However, the result is weird. dmesg shows me some huge numbers that does not make sense at all.

# dmesg
...
my_syscall_0
my_syscall_1 : 1111490392
my_syscall_2 : 1111490392, 1111490392

It seems like it is changing every time I execute the program.

Obviously, there's some problem in passing parameters. However, strace command shows me that the values are passed well.

# strace ./syscall
...
syscall_0x14F(0x7ffd21866538, 0x7ffd21866548, ....) = 0
...
syscall_0x150(0x1, 0, 0, 0, 0x7f9e1562f3a0, ....) = 0
...
syscall_0x14F(0x2, 0x3, 0x7f9e1562f3a0, ....) = 0
....

Brief

1. I made simple system calls.

2. Passing parameter to them are not working as the way they should be.

3. Question : Is there any problem in steps above, in order to add new system call?

4. Question : Is there any issues that I should aware when passing parameters to system call?

Thank you in advance.