Custom linux kernel syscall wrapper function

Question

i am writing a custom system call for linux kernel everything works fine with the function call and now i am trying to create a wrapper function in order to use the function normally in any program without using the syscall (call)

what i have done so far is

#include <stdlib.h>
#include<stdio.h>
#include<linux/unistd.h>
#include<errno.h>
#include <sys/types.h>
#include <unistd.h>
#include<string.h>
#include <linux/sched.h>
#include <linux/kernel.h>

long *__wrap_process_info(int myid , void *udata)
{
    return syscall(337 , myid , udata);
}

my system call returns -1 on error and 0 if executed correctly my question is , how to make the wrapper function return the syscall return value ? and ,do i need to include a main in the wrapper function ?

Eugene Sh. Eugene Sh. · Accepted Answer · 2015-03-04T17:10:37

Assuming that you are using the * as a wildcard and not pointer notation. Your implementation is already returning the value returned by the function syscall. In case there is an error, it's code is stored in errno variable, which you might want to copy to some additional parameter you will pass to your function:

long <???>__wrap_process_info(int myid , void *udata, long *err )
{
    long result;
    result = syscall(337 , myid , udata);
    *err = errno;
    return result;
}

Custom linux kernel syscall wrapper function

1 Answers