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{{Merge | Rebuilding OLPC kernel}} |
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== The OLPC kernel == |
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We use a modified version of the Linux kernel on the OLPC laptop. |
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OLPC OS [[Releases]] use our OLPC-modified version of the [[Linux]] kernel. |
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== The OLPC kernel git repository == |
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The OLPC kernel is maintained in git: |
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We use git to track changes that we've made, as well as to easily merge with Linus's (and others!) kernel tree. The git repository can be downloading with the following command: |
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* git://dev.laptop.org/olpc-kernel |
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* http://dev.laptop.org/git/olpc-kernel |
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Current maintainers: James Cameron. |
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<pre> |
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git clone git://dev.laptop.org/olpc-2.6 |
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</pre> |
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We work on specific git branches, which vary by hardware and operating system release. |
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Alternatively, you can use gitweb to view and search changes by going to: |
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{| border="1" cellspacing="0" cellpadding="2" width="100%" class="wikitable" |
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http://dev.laptop.org/git?p=olpc-2.6;a=summary |
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! operating system release |
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! git branches |
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|- |
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| (none) ARM XO-1.75 |
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| [http://dev.laptop.org/git/olpc-kernel/log/?h=olpc-5.0 olpc-5.0] |
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|- |
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| (none) i386 XO-1 XO-1.5 |
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| olpc-4.6 |
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|- |
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| [[14.1.0]] i386 XO-1 XO-1.5 |
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| olpc-3.10 |
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|- |
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| [[Android]] 5.x ARM XO-4 |
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| arm-3.5-android |
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|- |
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| [[Android]] 4.x ARM XO-4 |
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| arm-3.5-android-4.x |
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|- |
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| [[14.1.0]] [[13.2.1]] [[13.2.0]] [[13.1.0]] ARM XO-4 |
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| arm-3.5 |
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|- |
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| [[13.2.1]] [[13.2.0]] [[13.1.0]] [[12.1.0]] i386 XO-1 XO-1.5 |
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| x86-3.3 |
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|- |
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| [[14.1.0]] [[13.2.1]] [[13.2.0]] [[13.1.0]] [[12.1.0]] [[11.3.1]] ARM XO-1.75 |
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| [http://dev.laptop.org/git/olpc-3.0/log/?h=arm-3.0-wip arm-3.0-wip] |
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|- |
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| [[11.2.0]] i386 |
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| [http://dev.laptop.org/git/olpc-kernel/log/?h=olpc-2.6.35 olpc-2.6.35] |
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|- |
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| [[Release_notes/10.1.3|10.1.3]] i386 |
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| [http://dev.laptop.org/git/olpc-kernel/log/?h=olpc-2.6.31 olpc-2.6.31] |
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|} |
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Or looking at git history may identify which branches we are actively working on, and looking at the version of each branch compared to the kernel shipped in each release will help you identify which branch corresponds to which release(s). |
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Note that at the bottom of that page, there is a list of branches. We keep around different branches for a number of reasons; within a cloned git repository, you can switch to branch 'FOO' by running: |
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OLPC-specific configurations can be found at arch/x86/configs/ and arch/arm/configs/, these are what we use for automated builds and official releases. This configuration is also installed in /boot in our software releases. |
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<pre> |
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git checkout FOO |
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</pre> |
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Questions and contributions should be sent to the devel [[Mailing lists|mailing list]]. |
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The branches currently in use are: |
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=== Installing kernel RPMs === |
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* master - this is the default branch, and is the equivalent of cvs's HEAD. Code that we want in our future releases goes into this branch, and needs to be vetted before being committed. |
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* stable - this is the branch that we automatically pull kernels from when we build a release. It is usually a snapshot of the 'master' branch, although we sometimes cherry-pick fixes into it. |
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* powermgmt - this branch is where all the power management (suspend/resume) activity was happening. This code is now (mostly) in master; use that instead. |
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* origin - this is a git-ism; it basically marks where the 'master' branch was checked out from. It can be ignored. |
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* devtree - this branch is being used for development on the in-kernel OpenFirmware device tree. |
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<b>The following section only applies to pre-13.2 OS releases. On 13.2.0 and newer, installing a new kernel RPM on an XO will automatically activate it on the boot partition as well.</b> |
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The other branches are no longer used, and can be ignored. |
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Due to OLPC's versioned filesystem layout, installing a new kernel RPM is not enough for it to become active on reboot. This is explained in detail in /boot/README. To summarise, after installing a kernel you must copy it to a special place: |
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== OLPC kernel configuration == |
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If running a software release that uses partitions, first check to ensure that /bootpart is mounted (it should have several directories in it). If it isn't, mount it: |
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The Linux kernel has a config file that describes the various options that are built into the kernel. For OLPC, we store that in the root of the git repository, in the 'arch/i386/configs/olpc_defconfig' file. Via gitweb, it can be viewed (for the 'master' branch) here: |
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mount /dev/mmcblk0p1 /bootpart |
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Then: |
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http://dev.laptop.org/git?p=olpc-2.6;a=blob;f=arch/i386/configs/olpc_defconfig;h=f1675e86312eee9c1cc9e59ebefca91ff8afe979;hb=HEAD |
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rsync --delete-before -av /boot/ /bootpart/boot/ |
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If running a software release that does not use partitions: |
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For official OLPC kernel RPMS (and on OLPC OS images), the config ends up being installed as /boot/config-$VERS. This allows you to see how the currently running kernel is configured. |
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cp -a /boot/* /versions/boot/current/boot/ |
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== |
=== Building a kernel RPM === |
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* If using OLPC OS on your build host, install general development packages needed for kernel compiling: |
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We auto-build kernel RPMs every 30 mins, which means that new, shiny commit that just occurred will show up in the following places (depending upon branch): |
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yum install -y git rpmdevtools gcc make ncurses-devel m4 redhat-rpm-config |
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* Install build prerequisites: |
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yum install -y unifdef lzop dracut-modules-olpc |
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:* On Fedora 14 and older, [[Dracut-modules-olpc#Special considerations for Fedora 14 and older|be careful with dracut-modules-olpc]]. |
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* Install kernel prerequisites: |
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yum install -y libertas-usb8388-olpc-firmware \ |
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libertas-sd8686-firmware \ |
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libertas-sd8787-firmware |
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* Clone the git repository; you will need at least 1.5 GBytes free: |
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git clone git://dev.laptop.org/olpc-kernel |
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* Checkout the appropriate branch: |
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git checkout x86-3.3 |
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* Clean the source tree: |
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make clean distclean |
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* Make your source changes, |
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* Make any defconfig changes, for the laptop model, |
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** XO-1: arch/x86/configs/xo_1_defconfig |
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** XO-1.5: arch/x86/configs/xo_1.5_defconfig |
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** XO-1.75: arch/arm/configs/xo_175_defconfig |
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** XO-4: arch/arm/configs/xo_4_defconfig |
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* Commit all your changes, |
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* Run {{code|olpc/buildrpm}}, for the laptop model; |
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** XO-1: {{code|olpc/buildrpm 1.0}} |
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** XO-1.5: {{code|olpc/buildrpm 1.5}} |
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** XO-1.75: {{code|olpc/buildrpm 1.75}} |
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** XO-4: {{code|olpc/buildrpm 4}} |
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The output RPM files will be in olpc/RPMS/ which you can install on an XO, with the above versioned filesystem layout issues in mind. |
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* master - http://dev.laptop.org/~dilinger/master/ |
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* stable - http://dev.laptop.org/~dilinger/stable/ |
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=== Cross compiling === |
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The SRPMs (Source RPMs) are available in the same place. |
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Compiling ARM kernels on ARM is sloooow. It's very easy to cross-compile from a faster box. |
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The RPMs have the dates they were built, and the number of the build. For example, 'kernel-2.6.21-20070322.4.olpc.5fe63334a44da42.i586.rpm' was built on March 22, 2007. It was the 4th build on that day. The '5fe63334a44da42' is part of the git commit ID, if you're trying to match up what specific commits made it into the kernel. |
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Another option (a little more tricky) would be to use [http://crosstool-ng.org/ crosstool-ng] to build and install a cross-compiler. |
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The 'kernel-' RPMs contains all you need to boot into that new kernel; simply install it, reboot, and you're set. The 'kernel-devel-' RPMs contain headers necessary for building out-of-tree kernel modules. The 'kernel-debuginfo-' RPMs contain debugging info necessary for debugging the kernel with, say, systemtap. |
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==== Fedora ==== |
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To install your rpm: |
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rpm -ivh kernel-....rpm |
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On Fedora 16 or later, you can install an ARM cross compiler with: |
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cp -a /boot/* /versions/boot/current/boot/ |
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yum install gcc-arm-linux-gnu binutils-arm-linux-gnu |
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(If you omit the -a in the above recipe, the vmlinuz symlink will not be updated correctly) |
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To build the kernel, set these environment variables: |
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export ARCH=arm |
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export CROSS_COMPILE=armv7-linux-gnu- |
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==== Ubuntu ==== |
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On Ubuntu 13.04 or later, you can install an ARM cross compiler with: |
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apt-get install gcc-arm-linux-gnueabi |
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To build the kernel, set these environment variables: |
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export ARCH=arm |
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export CROSS_COMPILE=arm-linux-gnueabi- |
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Now you can compile kernels in the normal way. Here is a recipe: |
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mkdir -p /tmp/xo/lib/modules |
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mkdir -p /tmp/xo/bootpart/boot |
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cp arch/arm/configs/xo*fig .config |
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make oldconfig zImage |
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make modules |
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INSTALL_MOD_STRIP=1 INSTALL_MOD_PATH=/tmp/xo make modules_install |
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cp arch/arm/boot/zImage /tmp/xo/bootpart/boot/ |
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(cd /tmp/xo/bootpart/boot/ && ln -sf zImage vmlinuz) |
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After this, /tmp/xo can be tar'd up and extracted on the XO, on USB media, or on an NFS mount point. |
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=== Automatic RPM generation === |
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During development some branches are automatically built every 30 minutes (but only when there are new changes), the results are published at http://dev.laptop.org/~kernels/ |
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The directories you see there are also linked to [[RPM Dropbox|RPM dropboxes]], therefore are automatically published for inclusion in development builds. In other words, to get your kernel changes included in the current software release development efforts, you simply have to push your changes to the correct branch. |
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The utility behind this magic is olpc-kernel-builder: |
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* http://dev.laptop.org/git/projects/olpc-kernel-builder/ |
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* git://dev.laptop.org/projects/olpc-kernel-builder |
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* Maintainer: Chris Ball |
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When used under OLPC OS 13.2.0 on an XO-4, change the rpm_target to armv7hl in olpc/buildrpm, otherwise an armv7l rpm is generated, resulting in refusal to install with ''is intended for a different architecture''. This is only a packaging architecture and does not affect how the kernel is compiled. |
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Install mock to use olpc-kernel-builder |
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yum install -y mock |
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:Does not work under OLPC OS 13.2.0, mock fails to mount /proc in the chroot. --[[User:Quozl|Quozl]] 05:32, 21 February 2014 (UTC) |
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== Running development kernels == |
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Starting with 13.1.0 development builds, the /boot (or /bootpart/boot) area of the OS images has changed layout slightly. The kernel and initramfs are now <em>only</em> shipped in zip files, in order to reduce duplication for signed builds, and to remove duplication of firmware code in the olpc.fth boot script. |
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Dropping your own vmlinuz in place (or booting one from USB as described below, pointing at the internal disk for the initrd.img initramfs) will no longer work as standard, since this will cause the system to start looking for an unzipped initramfs too. The story is similar for initramfs development - if you drop a "raw" initramfs in place, you will need to ensure that an unzipped kernel is also installed. Just run, once, as root: |
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# olpc-dev-kernel |
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This will unzip the initramfs from the zip file and save it as <tt>initrd.img</tt>, and similarly it will unzip the kernel from its zip file and save it as <tt>vmlinuz</tt>. In both cases, if an existing initrd.img/vmlinuz file is present, it will not be overwritten. |
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Now drop your files in place as you have done so before, and the system will pick up the "unzipped" partner initramfs/kernel file. |
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One more detail to be aware of: if you put "unzipped" initramfs/kernel files in place using this method, you will no longer receive automatic firmware updates from bootfw.zip. This should only affect cases where you drop your own development kernel/initramfs in place, <em>then</em> upgrade the olpc-firmware RPM package, <em>and</em> expect that firmware upgrade to be automatically installed. |
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For more details, read the original proposal: [http://lists.laptop.org/pipermail/devel/2012-March/034439.html Removing duplication in /boot - affects kernel development]. |
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== Running vanilla kernels == |
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In late 2010, OLPC started a focused effort to upstream its kernel patches so that unmodified "vanilla" kernels run with complete functionality on the XO-1 and XO-1.5. |
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As of Linux-3.5 these efforts are mostly concluded - OLPC only carries a small number of patches, which will be upstreamed as time permits. |
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You may have to hunt around a bit to satisfy the configuration options so that the relevant drivers get built. Start with our defconfig in the appropriate branch. If in doubt, feel free to ask on the devel [[mailing lists|mailing list]] for someone's recent .config file. |
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== Boot your development kernel from USB == |
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When doing kernel development, it is time consuming to commit each small change, make an RPM, install RPM on the XO, reboot, and test. Instead, you can follow this procedure: |
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On your development system, prepare a USB disk as follows: |
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<b>XO-1.75 and XO-4:</b> |
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See the instructions at [[Kernel Building]] if you need to update modules in the initramfs. |
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* /boot/olpc.fth (download from [http://dev.laptop.org/~dsd/20111013/olpc.fth here]) |
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* /boot/zImage (your kernel that you want to test) |
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<b>XO-1.5 and XO-1</b> |
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== Building an OLPC kernel == |
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* /boot/olpc.fth (download for [http://dev.laptop.org/~dsd/20110221/olpc.fth.xo1 XO-1] or [http://dev.laptop.org/~dsd/20110221/olpc.fth.xo15 XO-1.5], be sure to rename to olpc.fth) |
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* /boot/irfs.img (download [http://dev.laptop.org/~dsd/20110221/irfs.img here] - this is a hacked OLPC initramfs which doesn't require /ofw support) |
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* /boot/bzImage (your kernel that you want to test) |
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Now plug this disk into your XO, turn it on, and the system will load the kernel from USB while booting the rest of the system as normal. If your new kernel crashes badly, just unplug the USB disk and boot the system again - it will revert to booting the "good" kernel from local disk. |
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So you've decided that you want to build an OLPC kernel? Are you certain? The kernel is filled with arcane magic and sharp pointy things that may draw blood. If you're really serious, see the [[Kernel Building]] page. |
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''Note: for XO-1 this only works with JFFS2. (small tweaks to olpc.fth or the hacked initramfs would be needed for ubifs).'' |
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== Building an OLPC kernel RPM == |
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[[Category:Subsystems]] |
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It takes a bit longer to build, but it's easier to distribute if you build a proper kernel RPM. The instructions for doing so are on the [[Rebuilding OLPC kernel]] page. |
Latest revision as of 08:04, 20 April 2019
The OLPC kernel
OLPC OS Releases use our OLPC-modified version of the Linux kernel.
The OLPC kernel is maintained in git:
Current maintainers: James Cameron.
We work on specific git branches, which vary by hardware and operating system release.
operating system release | git branches |
---|---|
(none) ARM XO-1.75 | olpc-5.0 |
(none) i386 XO-1 XO-1.5 | olpc-4.6 |
14.1.0 i386 XO-1 XO-1.5 | olpc-3.10 |
Android 5.x ARM XO-4 | arm-3.5-android |
Android 4.x ARM XO-4 | arm-3.5-android-4.x |
14.1.0 13.2.1 13.2.0 13.1.0 ARM XO-4 | arm-3.5 |
13.2.1 13.2.0 13.1.0 12.1.0 i386 XO-1 XO-1.5 | x86-3.3 |
14.1.0 13.2.1 13.2.0 13.1.0 12.1.0 11.3.1 ARM XO-1.75 | arm-3.0-wip |
11.2.0 i386 | olpc-2.6.35 |
10.1.3 i386 | olpc-2.6.31 |
Or looking at git history may identify which branches we are actively working on, and looking at the version of each branch compared to the kernel shipped in each release will help you identify which branch corresponds to which release(s).
OLPC-specific configurations can be found at arch/x86/configs/ and arch/arm/configs/, these are what we use for automated builds and official releases. This configuration is also installed in /boot in our software releases.
Questions and contributions should be sent to the devel mailing list.
Installing kernel RPMs
The following section only applies to pre-13.2 OS releases. On 13.2.0 and newer, installing a new kernel RPM on an XO will automatically activate it on the boot partition as well.
Due to OLPC's versioned filesystem layout, installing a new kernel RPM is not enough for it to become active on reboot. This is explained in detail in /boot/README. To summarise, after installing a kernel you must copy it to a special place:
If running a software release that uses partitions, first check to ensure that /bootpart is mounted (it should have several directories in it). If it isn't, mount it:
mount /dev/mmcblk0p1 /bootpart
Then:
rsync --delete-before -av /boot/ /bootpart/boot/
If running a software release that does not use partitions:
cp -a /boot/* /versions/boot/current/boot/
Building a kernel RPM
- If using OLPC OS on your build host, install general development packages needed for kernel compiling:
yum install -y git rpmdevtools gcc make ncurses-devel m4 redhat-rpm-config
- Install build prerequisites:
yum install -y unifdef lzop dracut-modules-olpc
- On Fedora 14 and older, be careful with dracut-modules-olpc.
- Install kernel prerequisites:
yum install -y libertas-usb8388-olpc-firmware \ libertas-sd8686-firmware \ libertas-sd8787-firmware
- Clone the git repository; you will need at least 1.5 GBytes free:
git clone git://dev.laptop.org/olpc-kernel
- Checkout the appropriate branch:
git checkout x86-3.3
- Clean the source tree:
make clean distclean
- Make your source changes,
- Make any defconfig changes, for the laptop model,
- XO-1: arch/x86/configs/xo_1_defconfig
- XO-1.5: arch/x86/configs/xo_1.5_defconfig
- XO-1.75: arch/arm/configs/xo_175_defconfig
- XO-4: arch/arm/configs/xo_4_defconfig
- Commit all your changes,
- Run olpc/buildrpm, for the laptop model;
- XO-1: olpc/buildrpm 1.0
- XO-1.5: olpc/buildrpm 1.5
- XO-1.75: olpc/buildrpm 1.75
- XO-4: olpc/buildrpm 4
The output RPM files will be in olpc/RPMS/ which you can install on an XO, with the above versioned filesystem layout issues in mind.
Cross compiling
Compiling ARM kernels on ARM is sloooow. It's very easy to cross-compile from a faster box.
Another option (a little more tricky) would be to use crosstool-ng to build and install a cross-compiler.
Fedora
On Fedora 16 or later, you can install an ARM cross compiler with:
yum install gcc-arm-linux-gnu binutils-arm-linux-gnu
To build the kernel, set these environment variables:
export ARCH=arm export CROSS_COMPILE=armv7-linux-gnu-
Ubuntu
On Ubuntu 13.04 or later, you can install an ARM cross compiler with:
apt-get install gcc-arm-linux-gnueabi
To build the kernel, set these environment variables:
export ARCH=arm export CROSS_COMPILE=arm-linux-gnueabi-
Now you can compile kernels in the normal way. Here is a recipe:
mkdir -p /tmp/xo/lib/modules mkdir -p /tmp/xo/bootpart/boot cp arch/arm/configs/xo*fig .config make oldconfig zImage make modules INSTALL_MOD_STRIP=1 INSTALL_MOD_PATH=/tmp/xo make modules_install cp arch/arm/boot/zImage /tmp/xo/bootpart/boot/ (cd /tmp/xo/bootpart/boot/ && ln -sf zImage vmlinuz)
After this, /tmp/xo can be tar'd up and extracted on the XO, on USB media, or on an NFS mount point.
Automatic RPM generation
During development some branches are automatically built every 30 minutes (but only when there are new changes), the results are published at http://dev.laptop.org/~kernels/
The directories you see there are also linked to RPM dropboxes, therefore are automatically published for inclusion in development builds. In other words, to get your kernel changes included in the current software release development efforts, you simply have to push your changes to the correct branch.
The utility behind this magic is olpc-kernel-builder:
- http://dev.laptop.org/git/projects/olpc-kernel-builder/
- git://dev.laptop.org/projects/olpc-kernel-builder
- Maintainer: Chris Ball
When used under OLPC OS 13.2.0 on an XO-4, change the rpm_target to armv7hl in olpc/buildrpm, otherwise an armv7l rpm is generated, resulting in refusal to install with is intended for a different architecture. This is only a packaging architecture and does not affect how the kernel is compiled.
Install mock to use olpc-kernel-builder
yum install -y mock
- Does not work under OLPC OS 13.2.0, mock fails to mount /proc in the chroot. --Quozl 05:32, 21 February 2014 (UTC)
Running development kernels
Starting with 13.1.0 development builds, the /boot (or /bootpart/boot) area of the OS images has changed layout slightly. The kernel and initramfs are now only shipped in zip files, in order to reduce duplication for signed builds, and to remove duplication of firmware code in the olpc.fth boot script.
Dropping your own vmlinuz in place (or booting one from USB as described below, pointing at the internal disk for the initrd.img initramfs) will no longer work as standard, since this will cause the system to start looking for an unzipped initramfs too. The story is similar for initramfs development - if you drop a "raw" initramfs in place, you will need to ensure that an unzipped kernel is also installed. Just run, once, as root:
# olpc-dev-kernel
This will unzip the initramfs from the zip file and save it as initrd.img, and similarly it will unzip the kernel from its zip file and save it as vmlinuz. In both cases, if an existing initrd.img/vmlinuz file is present, it will not be overwritten.
Now drop your files in place as you have done so before, and the system will pick up the "unzipped" partner initramfs/kernel file.
One more detail to be aware of: if you put "unzipped" initramfs/kernel files in place using this method, you will no longer receive automatic firmware updates from bootfw.zip. This should only affect cases where you drop your own development kernel/initramfs in place, then upgrade the olpc-firmware RPM package, and expect that firmware upgrade to be automatically installed.
For more details, read the original proposal: Removing duplication in /boot - affects kernel development.
Running vanilla kernels
In late 2010, OLPC started a focused effort to upstream its kernel patches so that unmodified "vanilla" kernels run with complete functionality on the XO-1 and XO-1.5.
As of Linux-3.5 these efforts are mostly concluded - OLPC only carries a small number of patches, which will be upstreamed as time permits.
You may have to hunt around a bit to satisfy the configuration options so that the relevant drivers get built. Start with our defconfig in the appropriate branch. If in doubt, feel free to ask on the devel mailing list for someone's recent .config file.
Boot your development kernel from USB
When doing kernel development, it is time consuming to commit each small change, make an RPM, install RPM on the XO, reboot, and test. Instead, you can follow this procedure:
On your development system, prepare a USB disk as follows:
XO-1.75 and XO-4:
- /boot/olpc.fth (download from here)
- /boot/zImage (your kernel that you want to test)
XO-1.5 and XO-1
- /boot/olpc.fth (download for XO-1 or XO-1.5, be sure to rename to olpc.fth)
- /boot/irfs.img (download here - this is a hacked OLPC initramfs which doesn't require /ofw support)
- /boot/bzImage (your kernel that you want to test)
Now plug this disk into your XO, turn it on, and the system will load the kernel from USB while booting the rest of the system as normal. If your new kernel crashes badly, just unplug the USB disk and boot the system again - it will revert to booting the "good" kernel from local disk.
Note: for XO-1 this only works with JFFS2. (small tweaks to olpc.fth or the hacked initramfs would be needed for ubifs).