Session 2 - Kernel: Code, Build, Run

Slides

Tasks

Important

Connect to the Linux virtual machine with:
- ssh student@spook.local

# Compile and boot Linux kernel #* wget kernel.org/pub/linux/kernel/v3.0/linux-3.4.4.tar.bz2 #* tar xjvf linux-3.4.4.tar.bz2 #* Check your current kernel version, and notice the target architecture # uname -a # cat /proc/version # cat /proc/cpuinfo #* Create .config file from i386_defconfig and check the options enabled # make defconfig #* Play around with make config and notice available options # What are the file systems compiled in kernel? # Is IPv6 support enabled ? #* Build kernel image and modules # make -j3 bzImage ; make -j3 modules #* Install kernel image # cp arch/x86/boot/bzImage /boot/vmlinuz-3.4.4 # cp .config /boot/config-3.4.4 # cp System.map /boot/System.map-3.4.4 #* Install modules # make modules_install #* Build initial ramdisk # cd /boot ; sudo mkinitramfs -o initrd.img-3.4.4 3.4.4 #* Update grub and reboot the system # sudo update-grub # reboot #* Boot into the new image and check current kernel version # cat /proc/version # Troubleshooting #* Notice that we can no longer connect, via ssh, to the new booted Linux kernel image inside the virtual machine. # Check the output of ifconfig or ip a s # Conclusion: There is no driver installed for the network card #* Boot into the old working image and figure out the network card type #

student@spook:~$ ethtool -i eth0
driver: pcnet32
version: 1.35
firmware-version: 
bus-info: 0000:00:11.0

#* Compile support for pcnet32 into the kernel # make menuconfig # Search for PCNET32 (use /PCNET32) # Select Y for AMD PCnet32 PCI support #* rebuild the bzImage as explained above, and reboot. # Say hello from the kernel #* Add a printk inside the sources (e.g init/main.c:512) #

 printk("Hello World!\n");

#* Recompile the image and reboot #* Check for the printk message # dmesg | grep Hello # Simple kernel module #* Analyze the source code for our simple module #* <code c simple.c>#include <linux/kernel.h> #include <linux/init.h> #include <linux/module.h> MODULE_DESCRIPTION(“My kernel module”); MODULE_AUTHOR(“Me”); MODULE_LICENSE(“GPL”); static int simple_init(void) { printk( KERN_DEBUG “Hi\n” ); return 0; } static void simple_exit(void) { printk( KERN_DEBUG “Bye\n” ); } module_init(simple_init); module_exit(simple_exit);</code> #* For compiling this module we need Makefile and Kbuid files. #* <code c Makefile>KDIR=/lib/modules/`uname -r`/build kbuild: make -C $(KDIR) M=`pwd` clean: make -C $(KDIR) M=`pwd` clean</code> #* <code make Kbuild>EXTRA_CFLAGS = -g obj-m = simple.o</code> #* Compile simple kernel module # make #* Insert it into the kernel # sudo insmod simple.ko #* Check if module works # dmesg | grep Hi # modinfo simple.ko # rmmod simple.ko #** dmesg | tail