Kernel module

Write a kernel module and syscall layer.

Kernel module

In the second lesson you add the kernel module. The kernel_init function initializes the kernel and prints a message. The syscall function doubles a system call number — a simple model of a syscall dispatcher.

In real kernels, syscall transitions from user space to kernel space; here a simplified version suffices. The kernel_init call is done at the start of main; this way the kernel is ready. The skeleton from the previous lesson is in the starting code; you add the new functions.

The syscall dispatcher pattern

A syscall dispatcher routes to different functions based on a number. In this project we use a simplified version: int syscall(int num) { return num * 2; }. A real dispatcher looks up a table and calls the relevant function.

The dispatcher pattern is implemented with a switch or a function pointer table. Here num * 2 simulates the dispatcher processing a call. kernel_init is called from main and signals the kernel is ready. These two functions form the kernel layer of the mini system.

Exercise Add the kernel module

Below the existing declarations, write void kernel_init(void) that prints printf("Çekirdek başladı\n"). Write int syscall(int num) that returns num * 2;. In main call kernel_init().

Show example solution

#include <stdio.h>
#include <string.h>

void kernel_init(void);
int parse_command(const char *cmd);
int security_check(const char *buf, int len);

void kernel_init(void) {
    printf("Çekirdek başladı\n");
}

int syscall(int num) {
    return num * 2;
}

int main(void) {
    printf("Proje başladı\n");
    kernel_init();
    return 0;
}

Test yourself

Complete the syscall return value

int syscall(int num) {
    return num * ____;
}

Show answer

int syscall(int num) {
    return num * 2;
}

What does kernel_init do?
- Reads a file
- Sets up a network connection
- Frees memory
- Initializes the kernel and prints a message
Show answer

Initializes the kernel and prints a message — kernel_init initializes the kernel and prints 'Çekirdek başladı'.
Match kernel function

kernel_init

Print kernel
syscall

Return num * 2
main

Control flow
printf

Print message

Next lesson: Compiler component

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