Kernel Compilation for ARM Processor

Raspberry Pi Kernel Compilation

Important note

The instructions provided below appears to outdated, are inconsistent and fail for the current version of the reffered repositories. Consider http://www.raspberrypi.org/documentation/linux/kernel/building.md, for which the cross-compilation instructions is confirmed to work. (19 March 2015, tools: 783eb21c, linux: c4ba28133).

Overview

This page explains how to rebuild the kernel image for the Raspberry Pi. There are two possible routes available:

1.     Compile on the Raspberry Pi itself

2.     Cross compile on another Linux system

Both of these routes are covered below, however, you are strongly recommended to follow the cross-compilation route. The low processing power of the Raspberry Pi means that a local compile will take many hours. A compilation of the latest kernel and modules took about 752 minutes (12h30m)!

If you want to compile an upstream kernel, rather than the Raspberry Pi Foundation's downstream kernel, please see RPi_Upstream_Kernel_Compilation for a few tips.

Example Checklist/Roadmap

This section serves to hold a new user's hand just a bit more than some of the other more generic information below in the document. To get more information on the steps in the roadmap, search this page for additional details. It assumes you can navigate filesystems, move files across systems, and have a general understanding of compiling linux kernels, filesystems, partitions, and block devices.

This series of steps yielded a successful custom/updated hardfp kernel to a stock Raspbian installation, cross compiled from an AMD 64-bit Debian system without regression on any kernel configuration options or requiring modified boot parameters. Be aware that in the worst case, you may need to overlay a stock set of kernel/modules/firmware on the Raspberry Pi if something fails. If you do not know how to do this, then a reimage of the SD card may be necessary. Assuming this is not an issue for your configuration, continue onward:

1.     Get the latest Raspberry Pi kernel source (https://github.com/raspberrypi/linux)

2.     Set an environment variable KERNEL_SRC to point to the location of the source (for example, KERNEL_SRC=/home/me/linux/ )

3.     Get the latest Raspberry Pi compiler (git clone https://github.com/raspberrypi/tools)

4.     Set an environment variable CCPREFIX to point to the location of tools (for example, CCPREFIX=/home/me/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi- )

5.     From the kernel clone location, clean the kernel source with "make mrproper"

6.     Pull the /proc/config.gz from the running Raspbian installation

7.     Prime the kernel with the old configuration by running "ARCH=arm CROSS_COMPILE=${CCPREFIX} make oldconfig"

8.     Modify the kernel configuration by either modifying the .config file or using "ARCH=arm CROSS_COMPILE=${CCPREFIX} make menuconfig"

9.     Build the new kernel by using "ARCH=arm CROSS_COMPILE=${CCPREFIX} make"

10.   Set an environment variable, MODULES_TEMP, to point to the location of the source (for example, MODULES_TEMP=/home/me/modules/ )

11.   Set aside the new kernel modules by using "ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make modules_install"

12.   From the tools clone location, in the mkimage directory, run "./imagetool-uncompressed.py ${KERNEL_SRC}/arch/arm/boot/zImage"

13.   Move the resulting kernel.img to the Raspberry Pi's /boot/ directory

14.   Package up the modules into an archive such that at the top level, the structure looks like this:

·        ./firmware

·        ./firmware/brcm

·        ./firmware/edgeport

·        ./firmware/emi26

·        ...

·        ./modules

·        ./modules/3.6.11+

·        ./modules/3.6.11+/kernel

·        ./modules/3.6.11+/kernel/lib

·        ./modules/3.6.11+/kernel/fs

·        ...

15.   Move the modules archive to the Raspberry Pi and extract them such that the aforementioned firmware and modules directories overwrite /lib/firmware and /lib/modules

16.   Get the latest Raspberry Pi firmware (git://github.com/raspberrypi/firmware.git)

17.   Transfer the following files from the firmware/boot directory to the Raspberry Pi /boot directory:

·        bootcode.bin

·        fixup.dat

·        start.elf

18.   Transfer the firmware/hardfp/opt directory to the Raspberry Pi /opt directory

19.   Reboot the Raspberry Pi

The Raspberry Pi should now boot with the newly configured/recompiled kernel.

Get the kernel source

The kernel source should be downloaded from the Raspberry Pi Linux section on GitHub. Although you could just compile the vanilla kernel from Kernel.org, it will not have the necessary drivers and modules for the Broadcom SoC on the Raspberry Pi. You can however apply patches from the vanilla kernel to the Raspberry Pi one - be prepared for potential compiler grumbles though!

On Jan 2014, the current is rpi-3.10.y. You can check this and other available versions by browsing Raspberry Pi Linux section on GitHub

You can download the source directly using Git. For the 3.10 branch:

git init

git clone --depth 1 git://github.com/raspberrypi/linux.git

And for the other stable code branch, change the numbers in the following to suit:

git init

git fetch git://github.com/raspberrypi/linux.git rpi-3.6.y:refs/remotes/origin/rpi-3.6.y

git checkout rpi-3.6.y

Or you can download a tarball from the same website:

Get a compiler

Next, you will need to get a version of GCC in order to build the kernel.

1. On the Raspberry Pi

Arch Linux

pacman -Syu

pacman -S gcc make

Funtoo or Gentoo Linux

emerge make bc screen

openSUSE Linux

Detailed openSUSE Raspberry Pi 12.3 Image 20130407 + 3.8.8 kernel hack tutorial witten (2013-04-22 updated) see: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=87&t=40664&p=331953#p331953 The kernel compile takes about 22 hours on Raspberry Pi Model B due massive module compiles. Include all IP_VS, ARPD, Fuse-zfs, Zram and more :-)

This works as well for Debian, Fedora Remix and others (just the package install command differs):

zypper install u-boot-tools sudo gcc automake autoconf bison gettext flex libncurses5 ncurses-devel

Raspbian and PiBang

apt-get update

apt-get -y dist-upgrade

apt-get -y install gcc make bc screen ncurses-dev git

cd /usr/src

mkdir GIT; cd GIT; git init; D=`date +"%m-%d-%Y"`

git fetch --depth=1 git://github.com/raspberrypi/linux.git rpi-3.8.y:refs/remotes/origin/rpi-3.8.y

git checkout rpi-3.8.y

tar cpf rpi-3.8.y.$D.tar   rpi-3.8.y

cd /usr/src

tar xpf  GIT/rpi-3.8.y.$D.tar

rm linux

ln -s linux-rpi-3.8.y linux

cd /usr/src/linux

kversion=$(make -s kernelrelease)

cp linux/.config .config_$kversion

cd /usr/src/

# Get config-3.8.7.ipvs+krb5+arpd.tar.bz2 from the tutorial:

wget http://www.raspberrypi.org/phpBB3/download/file.php?id=3174

# Copy the .config file to /usr/src/linux:

tar xpfj config-3.8.7.ipvs+krb5+arpd.tar.bz2

#Make the kernel and go sleep :-)

cd linux

make oldconfig

nohup make zImage dep modules &

#The next day: Install it.

cd /usr/src/linux

kversion=$(make -s kernelrelease)

echo $kversion

mkdir -p  /boot/$kversion

make ARCH=arm INSTALL_PATH=/boot/ install

cp System.map /boot/System.map-$kversion

cp System.map-$kversion /boot/System.map

make ARCH=arm modules_install INSTALL_MOD_PATH=/

make ARCH=arm INSTALL_PATH=/boot/ zinstall

cp .config /boot/config-$kversion

cp ./Module.symvers  /boot/symvers-$kversion

cp arch/arm/boot/Image /boot/kernel.img

2. Cross compiling from Linux

Please note that when cross-compiling, your compiler may not target the correct ARM processor by default. This will at best reduce performance, or worse, compile for a much newer processor resulting in illegal instructions in your code. The pre-built compiler or a custom-built compiler are recommended because of this. (For example, the latest GCC Linaro binary targets armv7-a by default, whereas the Raspberry Pi requires armv6kz). It is possible to add extra compiler options to the HOSTCFLAGS line in Makefile. The correct flags are shown on the software page - note that you may also need to add -marm if your compiler produces Thumb code by default.

Use the provided compiler

Download the pre-built bmc2708 compiler from the Raspberry Pi tools section on GitHub.

git clone git://github.com/raspberrypi/tools.git --depth 1

Or you can download a tarball from the website using this link.

Custom-built Linaro GCC

See Linaro GCC Compilation.

Ubuntu

apt-get install gcc-arm-linux-gnueabi make ncurses-dev

Funtoo or Gentoo Linux

crossdev -S -v -t arm-unknown-linux-gnueabi

Crossdev should create a cross-toolchain using the latest stable versions of the required packages. If it fails, you can specify exact versions by removing the "-S" flag and adding the "--b", "--g", "--k" and "--l" flags. On 2012-05-06, cross -S -v -A gnueabi armworks just fine.

Arch Linux

yaourt -S arm-linux-gnueabi-gcc

Cross compiling from OS X

Macports

The kernel source requires a case-sensitive filesystem. If you do not have a HFS+ case-sensitive partition that can be used, create a disk image with the appropriate format. Ensure the latest versin of Xcode and command line tools are installed from Apple Developer Connection Install macports

port install arm-none-eabi-gcc

port install arm-none-eabi-binutils

If you get an error message that elf.h is missing

sudo port install libelf && sudo ln -s /opt/local/include/libelf /usr/include/libelf

From opensource.apple.com, download and copy elf.h and elftypes.h to /usr/include

Edit elf.h and add

#define EM_S390           22   

#define R_386_NONE        0

#define R_386_32          1

#define R_386_PC32        2

#define R_ARM_NONE        0

#define R_ARM_PC24        1

#define R_ARM_ABS32       2

#define R_MIPS_NONE       0

#define R_MIPS_16         1

#define R_MIPS_32         2

#define R_MIPS_REL32      3

#define R_MIPS_26         4

#define R_MIPS_HI16       5

#define R_MIPS_LO16       6

#define EM_S390           22

#define R_MIPS_64         18

#define R_390_64          22

#define R_X86_64_64       1

#define R_SPARC_64        32

#define R_SH_DIR32        1

#define R_PPC_ADDR32      1

#define R_PPC64_ADDR64    38

#define R_IA64_IMM64      0x23

If you get a "SEGMENT_SIZE is undeclared" error open the Makefile and change the line:

NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)

to

NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) -Dlinux

Complete script requires raspberrypi.config to be in the same folder that you execute from.

sudo port install arm-none-eabi-gcc

sudo port install arm-none-eabi-binutils

sudo port install libelf && sudo ln -s /opt/local/include/libelf /usr/include/libelf

sudo curl http://opensource.apple.com/source/dtrace/dtrace-48/sys/elftypes.h?txt -o  /usr/include/elftypes.h

sudo curl http://opensource.apple.com/source/dtrace/dtrace-48/sys/elf.h?txt -o /usr/include/elf.h

#code to append to elf.h

echo "

#define EM_S390 22    

#define R_386_NONE 0

#define R_386_32 1

#define R_386_PC32 2

#define R_ARM_NONE 0

#define R_ARM_PC24 1

#define R_ARM_ABS32 2

#define R_MIPS_NONE 0

#define R_MIPS_16 1

#define R_MIPS_32 2

#define R_MIPS_REL32 3

#define R_MIPS_26 4

#define R_MIPS_HI16 5

#define R_MIPS_LO16 6

#define EM_S390 22

#define R_MIPS_64 18

#define R_390_64 22

#define R_X86_64_64 1

#define R_SPARC_64 32

#define R_SH_DIR32 1

#define R_PPC_ADDR32 1

#define R_PPC64_ADDR64 38

#define R_IA64_IMM64 0x23" > elf-append.h

sudo -s 'cat elf-append.h >> /usr/include/elf.h'

#Make a case sensitive 3 GB disk image, raspberrypi-kernel, and attach it:

hdiutil create -size 10g -type SPARSEBUNDLE -nospotlight -volname raspberrypi-kernel -fs "Case-sensitive Journaled HFS+" -attach ./raspberrypi-kernel.dmg

cp raspberrypi.config /Volumes/raspberrypi-kernel/

mkdir /Volumes/raspberrypi-kernel/src

cd /Volumes/raspberrypi-kernel/src

#Get source, either 1. from a ZIP file (faster), or 2. from Git

#1. From a ZIP file

curl https://codeload.github.com/raspberrypi/linux/zip/rpi-3.6.y -o ./rpi-3.6.y.zip

unzip rpi-3.6.y.zip

#2. From Git (disabled)

#git init

#git fetch git://github.com/raspberrypi/linux.git rpi-3.6.y:refs/remotes/origin/rpi-3.6.y

#git checkout rpi-3.6.y

cpu=$(sysctl hw.ncpu | awk '{print $2}')

cpup1=$((cpu+1))

cd /Volumes/raspberrypi-kernel/src/linux-rpi-3.6.y/

export CCPREFIX=/opt/local/bin/arm-none-eabi-

make mrproper

cp /Volumes/raspberrypi-kernel/raspberrypi.config .config

#Answer yes to all config options

#yes "" | make ARCH=arm CROSS_COMPILE=${CCPREFIX} oldconfig

make ARCH=arm CROSS_COMPILE=${CCPREFIX} -j$cpup1

#make ARCH=arm CROSS_COMPILE=${CCPREFIX} modules -j$cpup1

Yagarto

Download and install from here.

Perform the compilation

Firstly, ensure your build directory is clean:

make mrproper

Next, in all cases, you will want to get a working kernel configuration to start from. You can get the one running on the Raspberry Pi by typing the following (on the Raspberry Pi):

zcat /proc/config.gz > .config

Then copy .config into your build directory.

Alternatively, the default configuration is available in the downloaded kernel source in arch/arm/configs/bcmrpi_defconfig. Just copy this to .config in the build directory.

From this point on, if you are cross-compiling, set an environment variable CCPREFIX that points to the prefix of your compiler binary as each compiler will be named slightly differently.

export CCPREFIX=/path/to/your/compiler/binary/prefix-of-binary-

If you are building on the Raspberry Pi, remove ARCH=arm CROSS_COMPILE=${CCPREFIX} from each command.

Ensure that your configuration file is up-to-date:

make ARCH=arm CROSS_COMPILE=${CCPREFIX} oldconfig

If any configuration options have been added, you will be asked what set each option to. If you don't know the answer, just press enter to accept the default.

Optionally, if you want to make changes to the configuration, run this next:

make ARCH=arm CROSS_COMPILE=${CCPREFIX} menuconfig

Now you are ready to build:
(On the Raspberry Pi, type 'screen' to open a virtual screen. If you use it you can disconnect from the Raspberry Pi and compile overnight...)

make ARCH=arm CROSS_COMPILE=${CCPREFIX}

If you are on a multi-core system, you can make the build faster by appending -j<N> where <N> is the number of cores on your system plus one (that is, -j3 for two cores).

Find something else to get on with while the compilation takes place. On an average PC with the default configuration, this should take about 15 minutes.

The modules will be build with the following command.

make ARCH=arm CROSS_COMPILE=${CCPREFIX} modules

Transfer the build

The fully built kernel will be arch/arm/boot/Image. Copy your new kernel file into the Raspberry Pi boot partition, though preferably as a new file (such as kernel_new.img) just in case it doesn't work. If you're building on the Raspberry Pi, just copy the file to /boot. If you use a different filename, edit config.txt change the kernel line:

kernel=kernel_new.img

#kernel=kernel.img

Now you need to transfer the modules. Set an environment variable that points to a temporary module path.

export MODULES_TEMP=~/modules

In the build directory, run the following command:

make ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} modules_install

The contents of this directory, a single

lib

directory, should then be copied into the Raspberry Pi root directory, merging or overwriting

/lib

NOTE: If you have rebuilt the new kernel with exactly the same version as the one that's running, you'll need to remove the old modules first. Ideally this should be done offline by mounting the SD card on another system.

NOTE: The lib directory will have symlinks back to the kernel sources (lib/modules/<kernel-version>/source and lib/modules/<kernel-version>/build). If you have limited space on the SD card and don't intend to compile modules on the Raspberry Pi itself, you will probably want to remove those links before you transfer the lib directory. The size difference can be many hundreds of MB.

Your Raspberry Pi should now be ready to boot the new kernel. However, at this point it's recommended that you update your GPU firmware and libraries. This is required if you've just moved from 3.2 to 3.6 as the firmware interface has changed.

Get the firmware

The firmware and boot files should be updated at the same time to ensure that your new kernel works properly. Again, two branches are available:

·        master - This is the version of firmware currently used in Raspbian (that is, it works with the 3.2 kernel).

·        next - This is a development branch which provides a newer GPU firmware to work with the updated drivers in the 3.6 kernel.

You can either download the source directly using Git: You can download the firmware directly using Git. For the master branch:

git clone git://github.com/raspberrypi/firmware.git

And for the next branch:

git fetch git://github.com/raspberrypi/firmware.git next:refs/remotes/origin/next

Or you can download a tarball from the website using these links: master next

Transfer the firmware

Firstly, update the required boot files in the Raspberry Pi boot directory with those you've downloaded. These are:

·        bootcode.bin

·        fixup.dat

·        start.elf

Next, you need to copy the VC libraries over. There are two copies of this: one for hard float and one for soft float. To find the correct one, run the following command:

${CCPREFIX}gcc -v 2>&1 | grep hard

If something prints out, and you can see --with-float=hard, you need the hard float ones. NOTE: The current version of Raspbian uses hard float.

Remove the /opt/vc directory from the Raspberry Pi root, then:

·        For hard float, copy vc from the hardfp/opt directory into /opt in the Raspberry Pi root directory

·        Otherwise copy vc from the top-level opt directory into /opt in the Raspberry Pi root directory.

Note: The hard float vs soft float here refers only to the kernel itself, not the functionality it provides. Your applications will still be able to use hard floats. The kernel doesn't use floats anyway, so it is not something to worry about as long as you select the correct vcdirectory to copy.

Test your build

Power cycle your Raspberry Pi and check the following:

·        If you have the serial port on the GPIO expander wired up, you should see the kernel booting.

·        The screen works - the kernel boots and you get a login prompt.

·        The VC interface is working - if the 'OK' LED flashes regularly eight or so times every few seconds once the OS has booted, it's not. You can also test this by running vcgencmd measure_temp. If it prints "VCHI initialization failed", you have the a mismatch between the firmware, the VC libraries, and the kernel driver.

·        Run uname -a and check that your new kernel is the one that's running.

·        Make sure you don't have any odd error messages during boot that may indicate a module isn't working properly. If you see missed completion of cmd 18 regarding DMA transfers to the SD card, you can safely ignore it.

Build modules for the running kernel

You need the kernel sources for the currently running kernel to successfully build kernel modules for the Raspberry Pi. More specifically, only parts of the complete source, the so called kernel headers are needed. There are two ways to arrive at a state from which you can build kernel modules on the Raspberry Pi. 
1. is most suitable if you have been using Kernel sources from raspberrypi.org 
2. is using only mainline kernel stuff

1. Using rpi-source

rpi-source downloads a matching source for the running kernel. It supports rpi-update kernels and Raspian kernels.

Examples: https://github.com/notro/rpi-source/wiki/Examples-on-how-to-build-various-modules

2. Manually

If you have used or want to stick with a vanilla (mainline) kernel, there is a different way

You have been following the RPi_Upstream_Kernel_Compilation guide, correct? Great, let's move on: That guide is not using modules, so enable modules in make menuconfig first. Then execute

$ ARCH=arm CROSS_COMPILE=${CCPREFIX} chrt -i 0 make -j 8

$ ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} make modules_install

The second line will create the .ko files and it will create the necessary folder structure (/usr/src/linux/lib/modules/`uname -r`/[build|kernel|source]. build and source are symlinks to the kernel sources. kernel contains the module files (under some subdirectories).

Now you can continue with RPi_Upstream_Kernel_Compilation compiling the bootloader and so on. Finally also copy the used kernel sources onto the SD card, e.g. under /home/pi/linux

$ cp -av /usr/src/linux/ <sdcard-ext4-root>/home/pi/

Boot the Raspberry Pi, then execute

$ cd /home/pi

$ sudo chown -R pi:pi linux/

to change back ownership to you (this is necessary unless your username on your build machine is also "pi"...). Now copy /home/pi/linux/lib/modules/* to the correct

$ sudo cp -R /home/pi/linux/lib/modules/`uname -r`/ /lib/modules/

Correct the symlinks:

$ sudo cd /lib/modules/`uname -r`/

$ sudo rm build source

$ ln -s /home/pi/linux build

$ ln -s /home/pi/linux source

Now, we need to fix one more problem: During the cross-compilation build, a couple scripts were compiled for the host. We also need them for the Raspberry Pi. Still on the Pi, this can be checked with e.g.

$ file /home/pi/linux/scripts/recordmcount (returns something with x86-64)

$ cd /home/pi/linux/

$ make scripts

$ file /home/pi/linux/scripts/recordmcount (now returns something with 32-bit and ARM)