kernel_basics

COMMON ERRORS

1. Required key not available: Solution: disable Secure Boot in UEFI (BIOS) settings. Since Ubuntu kernel build 4.4.0-21.37 this can be fixed by running

   sudo apt install mokutil
   sudo mokutil --disable-validation
   

It will require to create a password. The password should be at least 8 characters long. After you reboot, UEFI will ask if you want to change security settings. Choose "Yes".

Help :- https://sourceware.org/systemtap/wiki/SecureBoot

https://askubuntu.com/questions/762254/why-do-i-get-required-key-not-available-when-install-3rd-party-kernel-modules

2. printk() not displaying message: Solution: adding '\n' to the printed text on the display function

3. Could not open device file: This is because the file was created in superuser mode while using the mknod command. Refer to #1.

Running Module

1. make to compile using Makefile
2. sudo insmod 'module-name'.ko to install the module
3. dmesg to display message

Using the ARM Cross Compiler

1. Install the arm-linux-gnueabi-gcc compiler

   sudo apt-get install gcc-arm-linux-gnueabi g++-arm-linux-gnueabi
   

2. Install qemu-arm-static

    sudo apt-get install qemu binfmt-support qemu-user-static
   

3. Make the binary file:

   make CC=arm-linux-gnueabi-gcc
   

   The Makefile can be found here: https://github.com/jadonk/gsoc-application

4. Execute the binary using QEMU emulator:

   qemu-arm-static ./helloworld.bin
   

5. To compile a normal C program:

    arm-linux-gnueabi-gcc helloworld.c