SYSCALL_DEFINE3(calc, int, a, int, b, char, op)
{
    long result = 0;
    int i;

    switch (op) {
    case '+': result = a + b; break;
    case '-': result = a - b; break;
    case '*': result = a * b; break;
    case '/':
        if (b == 0) return -EINVAL;
        result = a / b;
        break;
    case '%':
        if (b == 0) return -EINVAL;
        result = a % b;
        break;
    case '^':
        result = a ^ b;
        break;
    case 'p':   /* 表示 ** */
        result = 1;
        for (i = 0; i < b; i++)
            result *= a;
        break;
    default:
        return -EINVAL;
    }

    printk(KERN_INFO "sys_calc: %d %c %d = %ld\n", a, op, b, result);
    return result;
}

#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>

#define __NR_calc 548

int main(void)
{
    printf("3 + 4 = %ld\n", syscall(__NR_calc, 3, 4, '+'));
    printf("5 ** 3 = %ld\n", syscall(__NR_calc, 5, 3, 'p'));
    printf("10 %% 4 = %ld\n", syscall(__NR_calc, 10, 4, '%'));
    return 0;
}