• Slides

Important

• All work from now on will be done on a virtual machine. It should be installed on your lab workstation. To get it for home, use this link.
  • ssh student@spook.local

# Compile and boot Linux kernel #* Check your current kernel version, and notice the target architecture # uname -a # cat /proc/version # cat /proc/cpuinfo #* wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.10.tar.xz #* tar xf linux-3.10.tar.xz #* 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 # Note: the current linux version needs the 'bc' package that is not on the vm. Install it with sudo apt-get install bc. # make -j3 bzImage #* grab a coffee # make -j3 modules #* Install kernel image # sudo cp arch/x86/boot/bzImage /boot/vmlinuz-3.10.0 # sudo cp .config /boot/config-3.10.0 # sudo cp System.map /boot/System.map-3.10.0 #* Install modules # sudo make modules_install #* Build initial ramdisk # cd /boot ; sudo mkinitramfs -o initrd.img-3.10.0 3.10.0 #* Update grub and reboot the system # sudo update-grub # reboot #* Boot into the new image and check current kernel version # cat /proc/version

1. 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.
2. 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
3. Simple kernel module
   • Analyze the source code for our simple module

   • 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);

   • For compiling this module we need Makefile and Kbuid files.

   • Makefile

     KDIR=/lib/modules/`uname -r`/build
     kbuild:
             make -C $(KDIR) M=`pwd`
     clean:
             make -C $(KDIR) M=`pwd` clean

   • Kbuild

     EXTRA_CFLAGS = -g
     obj-m        = simple.o

   • 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 == Resources ==

* The Tanenbaum-Torvalds Debate