Linux memory

KernelTrap High Memory

LinuxMM HighMemory

Linux Memory

Process Memory

HighMem

• ZONE_HIGHMEM - dynamically mapped pages/processes > 896MB
  

LowMem

• ZONE_NORMAL - normal addressable pages 16-896MB
  
• ZONE_DMA - DMA-able pages <>

Process memory

Stack segment

• Parameters
  
• Return address
• Return frame pointer
  
• Local variables

Heap segment - dynamic memory allocation

Data segment

• BSS - uninitialized global data structures
  
• Data - initialized global variables and data structures

Text/code segment

All threads within a process share code and data segment.
All threads have their own stack.

Linux kernel cross compile with crosstool

Steps to build gcc/glibc toolchain using crosstool

• Download crosstool
• Set CC=gcc-3.4
• Change /bin/sh to bash
• Build crosstool

$ sh demo-powerpc-603.sh

Steps to cross compile Linux kernel using gcc/glibc toolchain

• Set the path to gcc/glibc toolchain
  
• Build Linux kernel
  

$ make ARCH=powerpc CROSS_COMPILE=powerpc-603-linux-gnu-

Linux kernel cross compile with buildroot

Steps to build gcc/uClibc toolchain using buildroot

• Download buildroot
  
• Change configuration to build for powerpc-603
  

$ make menuconfig

• Build buildroot
  

$ make

Steps to cross compile Linux kernel using gcc/uClibc toolchain

• Set the path to gcc/uClibc toolchain
  
• Build Linux kernel

$ make ARCH=powerpc CROSS_COMPILE=powerpc-linux-

Linux bootable disk image using EXTLINUX, debootstrap

Steps to create a bootable disk image using EXTLINUX, debootstrap, Linux kernel and run using QEMU

• Create disk image

$ dd if=/dev/zero of=rootfs.img bs=1M count=2560

• Create ext2 filesystem

$ mke2fs -j rootfs.img
$ tune2fs -c 0 -i 0 rootfs.img

• Mount disk image

$ sudo mount rootfs.img rootfs -o loop -t ext2

• Run debootstrap

$ sudo debootstrap --arch i386 intrepid rootfs

• Copy Linux kernel and initial ramdisk to boot directory
  

$ cp vmlinuz rootfs/boot
$ cp initrd.img rootfs/boot

• Install EXTLINUX bootloader
  

$ extlinux --install rootfs/boot
$ vi rootfs/boot/extlinux.conf
default linux
timeout 10
prompt 1

label linux
kernel /boot/vmlinuz
append initrd=/boot/initrd.img root=/dev/sda clocksource=kvm-clock

• Unmount disk image

$ sudo umount rootfs

• Run in QEMU
  

$ qemu -hda rootfs.img -m 1024

Linux bootable disk image using EXTLINUX, Busybox

Steps to create a minimal root filesystem using BusyBox and run Linux kernel using QEMU

• Download BusyBox and build with CONFIG_STATIC=y
• Create disk image

$ dd if=/dev/zero of=rootfs.img bs=1M count=10

• Make ext2 filesystem

$ mke2fs -j rootfs.img
$ tune2fs -c 0 -i 0 rootfs.img

• Mount disk image

$ sudo mount rootfs.img rootfs -o loop -t ext2

• Make boot directory

$ mkdir rootfs/boot

• Copy busybox to disk image

$ rsync -a busybox*/_install/ rootfs

• Create directories and files
  

$ cd rootfs
$ mkdir etc etc/init.d dev proc sys

$ cd etc
$ vi inittab
::sysinit:/etc/init.d/rcS
::askfirst:/bin/sh
$ chmod 644 inittab

$ cd init.d
$ vi rcS
#! /bin/sh
mount -a
$ chmod 744 rcS

$ cd ..
$ vi fstab
proc /proc proc defaults 0 0
$ chmod 644 fstab
$ cd ../..

• Unmount disk image
  

$ sudo umount rootfs

• Run in QEMU
  

$ qemu -hda rootfs.img -m 1024

Linux bootable disk image using EXTLINUX, buildroot

Steps to create a root filesystem using buildroot and run Linux kernel using QEMU

• Download buildroot

$ git clone git://git.buildroot.net/buildroot

• Update buildroot

$ cd buildroot
$ git pull

• Change configuration to build for i386

$ make menuconfig

• Build buildroot
  

$ make

• Run in QEMU
  

$ qemu -kernel /boot/vmlinuz -initrd /boot/initrd.img -hda binaries/uclibc/rootfs.i386.ext2 -append "root=/dev/sda rw" -m 1024

Steps to create a bootable disk image using EXTLINUX, buildroot, Linux kernel and run using QEMU

• Mount buildroot root filesystem

$ sudo mount binaries/uclibc/rootfs.i386.ext2 buildrootfs -o loop -t ext2

• Create disk image

$ dd if=/dev/zero of=rootfs.img bs=1M count=10

• Create ext2 filesystem

$ mke2fs -j rootfs.img
$ tune2fs -c 0 -i 0 rootfs.img

• Mount disk image

$ sudo mount rootfs.img rootfs -o loop -t ext2

• Copy buildroot to disk image
  

$ rsync -a buildrootfs/ rootfs

• Create boot directory
  

$ mkdir rootfs/boot

• Copy Linux kernel and initial ramdisk to boot directory
  

$ cp vmlinuz rootfs/boot
$ cp initrd.img rootfs/boot

• Install EXTLINUX bootloader
  

$ extlinux --install rootfs/boot
$ vi rootfs/boot/extlinux.conf
default linux
timeout 10
prompt 1

label linux
kernel /boot/vmlinuz
append initrd=/boot/initrd.img root=/dev/sda clocksource=kvm-clock

• Unmount disk image

$ sudo umount rootfs

• Run in QEMU
  

$ qemu -hda rootfs.img -m 1024

Linux kernel development using Eclipse/CDT and QEMU

Steps to build, install and run Linux kernel using QEMU.

• Download Linux kernel tree

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git linux-2.6.git

• Update Linux kernel tree

$ cd linux-2.6.git
$ git pull

• Prepare to build Linux kernel by reusing old Linux kernel config

$ cp /boot/config-`uname -r` .config
$ make oldconfig

• View Linux kernel config

$ make menuconfig

• Build Linux kernel

$ make

• Install Linux kernel modules

$ make modules_install

• Install Linux kernel

$ make install

• Build initial ramdisk

$ update-initramfs -k 2.6 -c

• Update GRUB

$ update-grub

• Browse source code

$ cscope -Rk

• Run new Linux kernel in QEMU

$ qemu -kernel /boot/vmlinuz-2.6 -initrd /boot/initrd.img-2.6 -hda /dev/zero -m 1024

• In QEMU, enter Ctrl+Alt+2 to get into QEMU monitor

• To check everything is ok
  

(qemu) info status

Steps to build and run Linux kernel using Eclipse/CDT and QEMU

• Install Eclipse/CDT and disable indexer
  

• Create new C Makefile project with default location pointing to linux-2.6

• Build Linux kernel in Eclipse

• Configure Eclipse debugger to use C/C++ application as vmlinuz, stop on startup at start_kernel(), use gdbserver with connection type tcp/1234
  

• Run QEMU with GDB-stub

$ qemu -S -s -kernel /boot/vmlinuz-2.6 -hda /dev/zero -m 1024

• Run Linux kernel in Eclipse

• Debug in Eclipse will stop at start_kernel

Linux startup sequence

BIOS

• System startup

Stage 1 boot loader

• MBR

Stage 2 boot loader

• GRUB - /boot/grub
• Loads kernel - /boot/vmlinuz
• Runs kernel - startup_32()

Kernel

• Runs non-architecture kernel - start_kernel()
• Loads initial ramdisk - /boot/initrd.img
• Loads driver modules - /lib/modules
• Loads root filesystem
• Runs /sbin/init

Init

• Reads /etc/inittab
• Reads /etc/event.d
• Runs default run level

Run levels

• /etc/rc0.d System halt
• /etc/rc1.d Single user
• /etc/rc2.d Full multi-user (default)
• /etc/rc3.d Full multi-user
• /etc/rc4.d Full multi-user
• /etc/rc5.d Full multi-user
• /etc/rc6.d System reboot

Mount filesystems

• /proc
• /sys

Linux resources

Linux.com
Linux.org
Kernel.org
Linux Kernel Newbies
Linux Journal

eLinux
CE Linux Forum
Embedded Linux conference
Linux Devices
Free Electrons
Tuxology
Scratchbox
Buildroot

http://www.ibm.com/developerworks/linux/library/l-linux-kernel/
http://www.linuxjournal.com/article/4395
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/index.html