mjhjmtu

Ubuntu18, linux kernel 4.18.13

I added a new system call with following steps:
1. edit ./arth/x86/entry/syscalls/syscall_64.tbl

401 common my_syscall sys_my_syscall

2. edit ./arth/x86/include/asm/syscalls.h

asmlinkage int sys_my_syscall(...)

3. and the ./mine/my_syscall.c, ./mine/my_syscall.h:

my_syscall.c

#include <linux/linkage.h>
asmlinkage int sys_my_syscall(int n) 
 printk("test %dn", n);
 return n;

my_syscall.h

#ifndef HELLO_WORLD_H
#define HELLO_WORLD_H
asmlinkage int sys_my_syscall(int n);
#endif

4. then use Makefile to make the new files in step 3.




5. compile the kernel.



6. 
   

   try my syscall with the following program:

   
   
   

   #include <stdio.h>
   #include <linux/unistd.h>
   int main() 
    int ret = syscall(401, 20);
    printf("ret %dn", ret);
    return 0;
   
   

   
   

And the syscall is successfully called. I can see the "test xxx" and "ret xxx" on my terminal. However, the parameter I pass into the syscall was wrong -- it is always an undefined number, 1018123134, -2021134452, and so on.

see step 2 above:

2. edit ./arth/x86/include/asm/syscalls.h

asmlinkage int sys_my_syscall(...)

You see (...), where I tried (char*), (int), (int, int), (char*, int) but none of them can make it correct. I dont know the principle here. Or maybe the problem is caused by other mistakes?

However, my friend tried the same method but succeeded in linux kernel 4.7.x! How could that be?

I have tried to search by google but failed to find the same problem. Could anyone help me to pass the parameter to my syscall? Thanks very much!

Ubuntu18, linux kernel 4.18.13