Difference between revisions of "RPi Kernel Compilation"

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{{Template:RPi_Software}}
 
{{Template:RPi_Software}}
 
  
 
= Overview =
 
= Overview =
 +
This page explains how to rebuild the kernel image for the RPi. There are two possible routes available:
 +
# Compile on the Raspberry Pi itself
 +
# Cross compile on another Linux system
  
First, you are going to get and build the linux kernel and its modules using a suitable compiler (a "cross-compiler" if you aren't building it on the same hardware you will be running it on) and then you are going to create a kernel image from the uncompressed kernel (Image) to place on the sd, along with the modules you build alongside it.
+
Both of these routes are covered below, however, you are strongly recommended to follow the cross compilation route. The low processing power of the RPi means that a local compile will take many hours.
  
See below for the various guides to get and compile a suitable kernel for your RPi, and then create a kernel.img according to the steps at the end.
+
= Get the kernel source =
 +
The kernel source should be downloaded from the [https://github.com/raspberrypi/linux RPI linux section on GitHub]. Although you could just compile the vanilla kernel from [http://www.kernel.org/ Kernel.org], it will not have the necessary drivers and modules for the Broadcom SoC on the RPi. You can however apply patches from the vanilla kernel to the RPi one - be prepared for potential compiler grumbles though!
  
 +
At the time of writing, two branches of interest are available:
 +
* '''rpi-3.2.27''' - This is the version of the kernel currently used in Raspbian.
 +
* '''rpi-3.6-y''' - This is a development branch based on the current vanilla kernel. It will eventually replace the 3.2 branch.
  
= Firmware =
+
You can download the source directly using git. For the 3.2 branch:
 +
<pre>
 +
git clone git://github.com/raspberrypi/linux.git
 +
</pre>
 +
and for the 3.6 branch:
 +
<pre>
 +
git fetch git://github.com/raspberrypi/linux.git rpi-3.6.y:refs/remotes/origin/rpi-3.6.y
 +
</pre>
 +
Or you can download a tarball from the website using these links: [https://github.com/raspberrypi/linux/archive/rpi-3.2.27.tar.gz rpi-3.2.27] [https://github.com/raspberrypi/linux/archive/rpi-3.6.y.tar.gz rpi-3.6.y]
  
* get the most recent firmware from github:
+
= Get a compiler =
 +
Next, you will need to get a version of GCC in order to build the kernel.
  
git clone https://github.com/raspberrypi/firmware/
+
== On the RPi ==
  
* copy the files from ''firmware/boot/'' to the boot partition of your SD card
+
=== Raspbian ===
+
<pre>
cd firmware/boot
+
apt-get update
cp arm128_start.elf arm192_start.elf arm224_start.elf bootcode.bin loader.bin start.elf /boot/
+
apt-get -y dist-upgrade
 
+
apt-get -y install gcc make
= Raspberry PI kernel compilation =
+
</pre>
 
+
You can compile the kernel on the board itself, but because of the limited resources it will take a lot of time. Alternatively you can crosscompile the kernel on another machine running Linux, Windows or OS X.
+
 
+
== Compiling on the Raspberry pi itself ==
+
 
+
=== Debian ===
+
 
+
apt-get update;
+
apt-get -y dist-upgrade;
+
apt-get -y install git tmux;
+
cd /opt/;
+
mkdir raspberrypi;
+
cd raspberrypi;
+
git clone --depth 1 https://github.com/raspberrypi/linux.git;
+
cd linux;
+
zcat /proc/config.gz > .config;
+
tmux new -s make;
+
nice make; nice make modules;
+
[Ctrl]+[B],[D]
+
############## … 5 hours later ...
+
tmux a -t m;
+
[Ctrl]+[D]
+
cp arch/arm/boot/Image /boot/kernel.img;
+
make ARCH=arm modules_install INSTALL_MOD_PATH=/
+
cd ../;
+
git clone --depth 1 https://github.com/raspberrypi/firmware/;
+
cd firmware/boot;
+
cp arm128_start.elf arm192_start.elf arm224_start.elf bootcode.bin loader.bin start.elf /boot/;
+
shutdown -r now;
+
  
 
=== Arch Linux ===
 
=== Arch Linux ===
 +
<pre>
 +
pacman -Syu
 +
pacman -S gcc make
 +
</pre>
  
==== getting the compiler ====
+
== Cross compiling from Linux ==
You will need GIT to clone the kernel source tree from GitHub, compiler (gcc) and GNU Make:
+
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 RPi requires armv6kz). It is possible to add extra compiler options to the <tt>HOSTCFLAGS</tt> line in <tt>Makefile</tt>. The correct flags are shown on the [[RPi_Software#Compiler|software page]] - note that you may also need to add <tt>-marm</tt> if your compiler produces Thumb code by default.
pacman -S git gcc make
+
  
(NOTE: git might be omitted if you decide to download sources in compressed format; this is far faster)
+
=== Use the provided compiler ===
 +
Download the pre-built bmc2708 compiler from the [https://github.com/raspberrypi/tools/tree/master/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi RPI tools section on GitHub].
 +
<pre>
 +
git clone git://github.com/raspberrypi/tools.git
 +
</pre>
 +
or you can download a tarball from the website using [https://github.com/raspberrypi/tools/archive/master.tar.gz this link].
  
==== getting the sources ====
+
=== Custom-built Linaro GCC ===
 +
See [[RPi_Linaro_GCC_Compilation|Linaro GCC Compilation]].
  
create a directory where you can work on  the raspberry pi software. I called mine "raspberrypi". Then clone the git repository.
+
=== Ubuntu ===
 
+
<pre>
mkdir raspberrypi
+
apt-get install gcc-arm-linux-gnueabi make ncurses-dev
cd raspberrypi
+
</pre>
git clone https://github.com/raspberrypi/linux.git
+
(NOTE: git might fail due to memory constraints; in this case creation of swap file might help. Be warned - this takes ages! To omit the revision history and reduce the download, you can add "--depth 1" to the end of the git clone command.)
+
 
+
Alternatively, download ZIP or TAR.GZ version of the sources from:
+
https://github.com/raspberrypi/linux/downloads
+
unpack and enter the extracted directory (this is your kernel directory - its sources to be precise)
+
 
+
==== configuring the kernel ====
+
Next, the kernel options are configured.  Either copy the cut down Raspberry Pi .config file from the kernel source configs directory:
+
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
+
 
+
Or alternatively, to use the configuration from a currently running Raspberry Pi image, connect to the target and extract the .config file.  Then copy the resultant .config file into the Linux kernel source root directory:
+
zcat /proc/config.gz > .config
+
cp .config <path to linux source root directory>
+
 
+
If needed - manual/additional configuration:
+
make menuconfig
+
 
+
==== compile the kernel ====
+
make
+
 
+
(NOTE: this will take around 6h; You might find GNU Screen useful)
+
 
+
== Cross compiling on a foreign machine==
+
 
+
=== Ubuntu Linux ===
+
 
+
==== getting the compiler ====
+
 
+
On Ubuntu Oneiric getting the arm cross compiler can be as easy as:
+
+
sudo apt-get install gcc-arm-linux-gnueabi make
+
sudo apt-get install git-core  #jhauser14905 -- might as well state the obvious, you need git installed! -- it's git-core on ubuntu. --REW
+
sudo apt-get install ncurses-dev #MatthewEveritt -- Had to install this to use menuconfig.
+
 
+
 
+
(TODO: Is this the right one? More packages required? I did this a while ago! TODO: Other distributions?)
+
 
+
==== getting the sources ====
+
 
+
create a directory where you can work on  the raspberry pi software. I called mine "raspberrypi". Then clone the git repository.
+
 
+
mkdir raspberrypi
+
cd raspberrypi
+
git clone https://github.com/raspberrypi/linux.git
+
cd linux
+
 
+
==== compiling ====
+
 
+
Next, the kernel options are configured.  Either copy the cut down Raspberry Pi .config file from the kernel source configs directory:
+
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
+
 
+
Or alternatively, to use the configuration from a currently running Raspberry Pi image, connect to the target and extract the .config file.  Then copy the resultant .config file into the Linux kernel source root directory:
+
zcat /proc/config.gz > .config
+
cp .config <path to linux source root directory>
+
 
+
Configure the kernel with the copied .config file by running oldconfig:
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- oldconfig
+
 
+
If manual/additional configuration of kernel options are needed run menuconfig:
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- menuconfig
+
 
+
Then build the kernel:
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- -k
+
 
+
You can use the "-j" flag to improve compilation time. If you have a dual core machine you can use "-j 3", for a quad core machine you can use "-j 6", and so on.
+
 
+
If you get the error messages that arm-linux-gnueabi-gcc cannot be found when running make, run the following command:
+
 
+
sudo apt-get install gcc-arm-linux-gnueabi
+
  
 
=== Gentoo Linux ===
 
=== Gentoo Linux ===
 +
<pre>
 +
crossdev -S -v -t arm-unknown-linux-gnueabi
 +
</pre>
  
==== getting the compiler ====
+
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, <tt>cross -S -v -A gnueabi arm</tt> works just fine.
 
+
Build the cross toolchain:
+
crossdev -S -v -t arm-unknown-linux-gnueabi
+
 
+
theBuell: on 2012-05-06, cross -S -v -A gnueabi arm works just fine
+
 
+
This command 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. For the exact usage refer to the crossdev manpage. A good starting point for figuring out the right versions are those which are stable for the arm architecture.
+
 
+
==== getting the sources ====
+
 
+
create a directory where you can work on  the raspberry pi software. I called mine "raspberrypi". Then clone the git repository.
+
 
+
mkdir raspberrypi
+
cd raspberrypi
+
git clone https://github.com/raspberrypi/linux.git
+
cd linux
+
 
+
==== compiling ====
+
 
+
Next you have to configure the kernel:
+
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- oldconfig
+
 
+
Then building the kernel:
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- -k
+
 
+
You can use the "-j" flag to improve compilation time. If you have a dual core machine you can use "-j 3", for a quad core machine you can use "-j 6", and so on.
+
  
 
=== Arch Linux ===
 
=== Arch Linux ===
 +
<pre>
 +
yaourt -S arm-linux-gnueabi-gcc
 +
</pre>
  
==== getting the compiler ====
+
== Cross compiling from OSX ==
You will need GIT to clone the kernel source tree from GitHub:
+
=== Macports ===
pacman -S git
+
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 latest Xcode and command line tools are installed from [http://developer.apple.com/downloads Apple Developer Connection]
Build the cross toolchain:
+
Install [http://guide.macports.org/#installing macports]
arm-linux-gnueabi-gcc is on the AUR. If you use yaourt:
+
<pre>
 
+
port install arm-none-eabi-gcc
yaourt -S arm-linux-gnueabi-gcc
+
port install arm-none-eabi-binutils
 
+
</pre>
Yaourt is recommended as it will build all dependencies.
+
 
+
==== getting the sources ====
+
 
+
create a directory where you can work on  the raspberry pi software. I called mine "raspberrypi". Then clone the git repository.
+
 
+
mkdir raspberrypi
+
cd raspberrypi
+
git clone https://github.com/raspberrypi/linux.git
+
cd linux
+
 
+
==== compiling ====
+
 
+
Next you have to configure the kernel:
+
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- oldconfig
+
 
+
Then building the kernel:
+
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- -k
+
 
+
You can use the "-j" flag to improve compilation time. If you have a dual core machine you can use "-j 3", for a quad core machine you can use "-j 6", and so on.
+
 
+
=== Windows ===
+
 
+
TODO
+
 
+
=== OS X ===
+
 
+
==== getting the compiler ====
+
Ensure latest Xcode and command line tools are installed from [http://developer.apple.com/downloads Apple Developer Connection] then
+
Downoad and install an GNU ARM toolchain such as [http://www.yagarto.de/#downloadmac yagarto]
+
 
+
Another option is the MacPorts arm-none-eabi-*:
+
 
+
ARM gcc:
+
 
+
port install arm-none-eabi-gcc
+
 
+
binutils:
+
 
+
port install arm-none-eabi-binutils
+
 
+
==== getting the sources ====
+
 
+
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 then clone the repository into the mounted image.
+
 
+
Otherwise, create a directory where you can work on  the raspberry pi software. I called mine "raspberrypi". Then clone the git repository.
+
 
+
mkdir raspberrypi
+
cd raspberrypi
+
git clone https://github.com/raspberrypi/linux.git
+
cd linux
+
 
+
==== compiling ====
+
 
+
Next you have to configure the kernel: (the running kernel config can be found in <code>/proc/config.gz</code> on your RPi)
+
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config
+
make ARCH=arm CROSS_COMPILE=/path/to/yagarto/bin/arm-none-eabi- oldconfig
+
 
+
or if you used the MacPorts
+
make ARCH=arm CROSS_COMPILE=/opt/local/bin/arm-none-eabi- oldconfig
+
 
+
Then building the kernel:
+
make ARCH=arm CROSS_COMPILE=/path/to/yagarto/bin/arm-none-eabi- -k
+
 
+
or if you used the MacPorts
+
make ARCH=arm CROSS_COMPILE=/opt/local/bin/arm-none-eabi- -k
+
 
+
You can use the "-j" flag to improve compilation time. If you have a dual core machine you can use "-j 3", for a quad core machine you can use "-j 6", and so on. (Don't use these for the oldconfig option because it messes up the input and output).
+
  
 
'''If you get an error message that elf.h is missing'''
 
'''If you get an error message that elf.h is missing'''
 
install [http://guide.macports.org/#installing macports]
 
install libelf and symlink to /usr/libelf:
 
 
  sudo port install libelf && sudo ln -s /opt/local/include/libelf /usr/include/libelf
 
  sudo port install libelf && sudo ln -s /opt/local/include/libelf /usr/include/libelf
copy [http://opensource.apple.com/source/dtrace/dtrace-48/sys/elf.h?txt elf.h] and [http://opensource.apple.com/source/dtrace/dtrace-48/sys/elftypes.h?txt elftypes.h] to /usr/include
+
From opensource.apple.com, download and copy [http://opensource.apple.com/source/dtrace/dtrace-48/sys/elf.h?txt elf.h] and [http://opensource.apple.com/source/dtrace/dtrace-48/sys/elftypes.h?txt elftypes.h] to /usr/include
  
 
Edit elf.h and add
 
Edit elf.h and add
Line 269: Line 101:
 
  #define R_MIPS_HI16      5
 
  #define R_MIPS_HI16      5
 
  #define R_MIPS_LO16      6
 
  #define R_MIPS_LO16      6
 
 
'''If you get a "SEGMENT_SIZE is undeclared" error'''
 
'''If you get a "SEGMENT_SIZE is undeclared" error'''
 
 
open the Makefile and change the line:
 
open the Makefile and change the line:
 
 
  NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 
  NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 +
to
 +
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) -Dlinux
  
to
+
=== Yagarto ===
 +
Download and install from [http://www.yagarto.de/#downloadmac here].
  
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) -Dlinux
+
= Perform the compilation =
 +
Firstly, ensure your build directory is clean:
 +
<pre>
 +
make mrproper
 +
</pre>
 +
 
 +
Next, in all cases, you will want to get a working kernel configuration to start from. You can get the one running on the RPi by typing the following (on the RPi):
 +
<pre>
 +
zcat /proc/config.gz > .config
 +
</pre>
 +
then copy <tt>.config</tt> into your build directory.
 +
 
 +
Alternatively, the default configuration is available in the downloaded kernel source in <tt>arch/arm/configs/bcmrpi_defconfig</tt>. Just copy this to <tt>.config</tt> in the build directory.
 +
 
 +
From this point on, if you are cross-compiling, please substitute <tt><your_compiler></tt> with your compiler binary prefix (e.g. <tt>arm-bcm2708hardfp-linux-gnueabi-</tt>) as each compiler will be named slightly differently. If you are building on the RPi, remove <tt>ARCH=arm CROSS_COMPILE=<your_compiler></tt> from each command.
 +
 
 +
Ensure that your configuration file is up-to-date:
 +
<pre>
 +
make ARCH=arm CROSS_COMPILE=<your_compiler> oldconfig
 +
</pre>
 +
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:
 +
<pre>
 +
make ARCH=arm CROSS_COMPILE=<your_compiler> menuconfig
 +
</pre>
 +
 
 +
Now you are ready to build:
 +
<pre>
 +
make ARCH=arm CROSS_COMPILE=<your_compiler>
 +
</pre>
 +
If you are on a multi-core system, you can make the build faster by appending <tt>-j<N></tt> where <tt>N</tt> is the number of cores on your system plus one.
 +
 
 +
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.
 +
 
 +
= Prepare the image file =
 +
Because of the way the memory addresses are arranged in the Broadcom SoC, you will need to prepare the compiled image for use.
 +
 
 +
If you haven't got the tools directory from the Git repo, please do so now:
 +
<pre>
 +
git clone git://github.com/raspberrypi/tools.git
 +
</pre>
 +
or you can download a tarball from the website using [https://github.com/raspberrypi/tools/archive/master.tar.gz this link].
 +
 
 +
In the tools set, there is a folder called <tt>mkimage</tt>. Enter this directory, then run the following:
 +
<pre>
 +
./imagetool-uncompressed.py <your_kernel_build_directory>/arch/arm/boot/zImage
 +
</pre>
 +
 
 +
This will output a file called <tt>kernel.img</tt>.
 +
 
 +
= Transfer the build =
 +
Copy your new <tt>kernel.img</tt> file into the RPi boot partition, though preferably as a new file (such as <tt>kernel_new.img</tt>) just in case it doesn't work. If you're building on the RPi, just copy the file to <tt>/boot</tt>. If you use a different filename, edit <tt>config.txt</tt> change the kernel line:
 +
<pre>
 +
kernel=kernel_new.img
 +
#kernel=kernel.img
 +
</pre>
 +
 
 +
Now you need to transfer the modules. In the build directory, run the following (substituting <tt><modules_path></tt> for a folder somewhere (e.g. <tt>~/modules</tt>):
 +
<pre>
 +
ARCH=arm CROSS_COMPILE=<your_compiler> make modules_install INSTALL_MOD_PATH=<modules_path>
 +
</pre>
 +
 
 +
The contents of this directory should then be copied into the RPi root directory. 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.
  
=== Transferring The Build ===
+
Your RPi 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'''.
  
Then you have to transfer this img file to the /boot directory and install the compiled modules. Unfortunately the compiled modules are not in a single place, there are two options of installing them.
+
= 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 (i.e. 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.
  
Boot your RaspberryPi and mount the <code>linux</code> directory over the network using sshfs:
+
You can either download the source directly using git:
cd /mnt
+
You can download the firmware directly using git. For the master branch:
mkdir linux
+
<pre>
sshfs <user>@<host>:<path/to/linux> linux
+
git clone git://github.com/raspberrypi/firmware.git
cd linux
+
</pre>
make install
+
and for the next branch:
make modules_install
+
<pre>
 +
git fetch git://github.com/raspberrypi/firmware.git next:refs/remotes/origin/next
 +
</pre>
 +
Or you can download a tarball from the website using these links: [https://github.com/raspberrypi/firmware/archive/master.tar.gz master] [https://github.com/raspberrypi/firmware/archive/next.tar.gz next]
  
If you got "Permission denied" when doing <code>cd linux</code>, try:
+
= Transfer the firmware =
sudo sh -c "cd linux ; make modules_install"
+
Firstly, update the required boot files in the RPi <tt>boot</tt> directory with those you've downloaded. These are:
 +
* bootcode.bin
 +
* fixup.dat
 +
* start.elf
  
If that is not an option, you can also install the modules into a temporary folder:
+
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 (substituting the program name for your compiler binary as required):
mkdir /tmp/modules
+
<pre>
make ARCH=arm modules_install INSTALL_MOD_PATH=/tmp/modules
+
arm-none-linux-gnueabi-gcc -v 2>&1 | grep hard
 +
</pre>
  
Now you have to copy the contents of that directory to /lib/modules on the SD card.
+
If something prints out, and you can see <tt>--with-float=hard</tt>, you need the hard float ones. NOTE: The current version of Raspbian uses hard float.
scp linux/arch/arm/boot/Image <user>@<host>:/boot/kernel.img
+
scp -r /tmp/modules/* <user>@<host>://lib/modules/
+
  
Once you've done those two steps, you are ready to put the SD card in and try booting your new system!
+
Remove the <tt>/opt/vc</tt> directory from the RPi root, then:
 +
* For hard float, copy <tt>vc</tt> from the <tt>hardfp/opt</tt> directory into <tt>/opt</tt> in the RPi root directory
 +
* Otherwise copy <tt>vc</tt> from the top-level <tt>opt</tt> directory into <tt>/opt</tt> in the RPi root directory.
  
=References=  
+
= Test your build =
<references/>
+
Power cycle your RPi 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 <tt>vcgencmd measure_temp</tt>. If it prints "VCHI initialization failed", you have the a mismatch between the firmware, the VC libraries, and the kernel driver.
 +
* Run <tt>uname -a</tt> 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 <tt>missed completion of cmd 18</tt> regarding DMA transfers to the SD card, you can safely ignore it.
  
 
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[[Category:RaspberryPi]]
 
[[Category:RaspberryPi]]

Revision as of 17:58, 25 November 2012

Back to the Hub.


Software & Distributions:

Software - an overview.

Distributions - operating systems and development environments for the Raspberry Pi.

Kernel Compilation - advice on compiling a kernel.

Performance - measures of the Raspberry Pi's performance.

Programming - programming languages that might be used on the Raspberry Pi.

Overview

This page explains how to rebuild the kernel image for the RPi. 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 RPi means that a local compile will take many hours.

Get the kernel source

The kernel source should be downloaded from the RPI 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 RPi. You can however apply patches from the vanilla kernel to the RPi one - be prepared for potential compiler grumbles though!

At the time of writing, two branches of interest are available:

  • rpi-3.2.27 - This is the version of the kernel currently used in Raspbian.
  • rpi-3.6-y - This is a development branch based on the current vanilla kernel. It will eventually replace the 3.2 branch.

You can download the source directly using git. For the 3.2 branch:

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

and for the 3.6 branch:

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

Or you can download a tarball from the website using these links: rpi-3.2.27 rpi-3.6.y

Get a compiler

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

On the RPi

Raspbian

apt-get update
apt-get -y dist-upgrade
apt-get -y install gcc make

Arch Linux

pacman -Syu
pacman -S gcc make

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 RPi 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 RPI tools section on GitHub.

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

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

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 arm works just fine.

Arch Linux

yaourt -S arm-linux-gnueabi-gcc

Cross compiling from OSX

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 latest 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 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

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

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 RPi by typing the following (on the RPi):

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, please substitute <your_compiler> with your compiler binary prefix (e.g. arm-bcm2708hardfp-linux-gnueabi-) as each compiler will be named slightly differently. If you are building on the RPi, remove ARCH=arm CROSS_COMPILE=<your_compiler> from each command.

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

make ARCH=arm CROSS_COMPILE=<your_compiler> 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=<your_compiler> menuconfig

Now you are ready to build:

make ARCH=arm CROSS_COMPILE=<your_compiler>

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.

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.

Prepare the image file

Because of the way the memory addresses are arranged in the Broadcom SoC, you will need to prepare the compiled image for use.

If you haven't got the tools directory from the Git repo, please do so now:

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

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

In the tools set, there is a folder called mkimage. Enter this directory, then run the following:

./imagetool-uncompressed.py <your_kernel_build_directory>/arch/arm/boot/zImage

This will output a file called kernel.img.

Transfer the build

Copy your new kernel.img file into the RPi 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 RPi, 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. In the build directory, run the following (substituting <modules_path> for a folder somewhere (e.g. ~/modules):

ARCH=arm CROSS_COMPILE=<your_compiler> make modules_install INSTALL_MOD_PATH=<modules_path>

The contents of this directory should then be copied into the RPi root directory. 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.

Your RPi 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 (i.e. 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 RPi 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 (substituting the program name for your compiler binary as required):

arm-none-linux-gnueabi-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 RPi root, then:

  • For hard float, copy vc from the hardfp/opt directory into /opt in the RPi root directory
  • Otherwise copy vc from the top-level opt directory into /opt in the RPi root directory.

Test your build

Power cycle your RPi 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.