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DRAFT
====== Generality ======
A side note, at the Kernel level soft (armel)/[[https://wiki.linaro.org/Linaro-arm-hardfloat|hard float]] (armhf) doesn't matter, it matters at the userspace space level when passing function arguments (in hard float they are passed via FPU registers). [[http://linaro.com|Linaro]] has made a [[https://wiki.linaro.org/OfficeofCTO/HardFloat/Benchmarks|benchmark]] about this subject.

[[http://en.wikipedia.org/wiki/Nvidia_Tegra#Tegra_2_series|NVidia's Tegra2]]((http://www.nvidia.com/object/tegra-2.html)), which is dual-core [[http://arm.com|ARM]] [[http://en.wikipedia.org/wiki/Cortex-A9|Cortex-A9]], supports only [[http://en.wikipedia.org/wiki/ARM_architecture#VFP|VFPv3]] ((http://www.arm.com/products/processors/technologies/vector-floating-point.php)) and **not** [[http://en.wikipedia.org/wiki/ARM_architecture#Advanced_SIMD_.28NEON.29|NEON]] ((http://www.arm.com/products/processors/technologies/neon.php)) extensions which are more powerful.

As of 2012/02/18, the most stable kernel is 3.0.19, and [[http://gitorious.org/~marvin24/ac100/marvin24s-kernel/|Marc Dietrich]], the ac100 kernel maintainer, started to work on [[http://gitorious.org/~marvin24/ac100/marvin24s-kernel/commits/chromeos-ac100-3.2-exp|kernel 3.2.x series]] for AC100.

The most hotspot in kernel development is NVEC driver (incomplete implementation and marginal stability issue), sound driver (noise annoyance, automatic switch between Speaker/Headphone (not implemented at all in ASoC but can be easily done with a userspace daemon)) and ''rt2800usb'' Wifi driver (some stability issues and high stress on specific memory pool (reduced by **echo 32000 > /proc/sys/vm/min_free_kbytes**)).


====== Recompiling a Kernel ======
Before doing this operation, try an already compiled kernel for less harsh, here is some link to pick it:

=====Ubuntu=====

[[http://startx.ro/~jani/|Kernels cooked by Jani Monoses]]

http://launchpadlibrarian.net/89568135/linux-image-3.0.8-4-ac100_3.0.8-4.3_armel.deb

https://launchpad.net/ubuntu/+source/linux-ac100/3.0.19-1.2/+build/3219594/+files/linux-image-3.0.19-1-ac100_3.0.19-1.2_armhf.deb
=====Debian=====

[[http://lists.debian.org/debian-arm/2011/07/msg00049.html|http://people.debian.org/~jak/ac100/]]
=====Fedora=====

http://dmarlin.fedorapeople.org/yum/f15/arm/os/Packages/kernel-tegra-2.6.40.3-2.09.fc15.armv7hl.rpm

[[http://zenit.senecac.on.ca/wiki/index.php/Fedora_ARM_Koji_Buildsystem|Fedora ARM Koji Buildsystem]]

[[http://arm.koji.fedoraproject.org/koji/packageinfo?packageID=3547|Information for package kernel]]

[[http://arm.koji.fedoraproject.org/packages/kernel/3.2.2/1.fc17/armv7hl/kernel-3.2.2-1.fc17.armv7hl.rpm|kernel-3.2.2-1.fc17.armv7hl.rpm]]

=====RedSleeve=====

TOO OLD

ftp://ftp.redsleeve.org/pub/yum/os/Packages/kernel-2.6.32-220.2.1.el6.kirkwood.armv5tel.rpm

=====Others=====

You can extract zImage and corresponding modules from these packages.

=== From RPM ===

==Using alien==
  * ''alien --to-tgz linux-image-XXX.rpm''
  * ''tar xf linux-image-XXX.tgz''

=== From DEB ===
Get a kernel deb, for example http://startx.ro/~jani/linux-image-3.0.19-1-ac100_3.0.19-1.1_armel.deb

==Using alien==
  * ''alien --to-tgz linux-image-3.0.19-1-ac100_3.0.19-1.1_armel.deb''
  * ''tar xf linux-image-3.0.19-1-ac100-3.0.19.tgz''
==Or using file-roller==
  * ''file-roller linux-image-3.0.19-1-ac100_3.0.19-1.1_armel.deb'' (Can non Ubuntu versions of file-roller also read debs?)
==Or using dpkg==
  * ''dpkg -X linux-image-3.0.19-1-ac100_3.0.19-1.1_armel.deb''

===Afterwards===
  * ''cp -Rp lib/modules/3.0.19-1-ac100 /<your rootfs>/lib/modules''
  * ''abootimg -u /tmp/alien/part-6.img -k /tmp/alien/tgz/boot/vmlinuz-3.0.19-1-ac100''
===== Compilation environment consideration =====

[[toolchain|Cross-compiling]] and native.

===== 2.6.38 Kernel series =====
<code>
git clone -b chromeos-ac100-2.6.38 git://gitorious.org/~marvin24/ac100/marvin24s-kernel.git
cd marvin24s-kernel
make paz00_defconfig zImage modules modules_install INSTALL_MOD_PATH=/mnt/mmcblk1p1
abootimg -u /tmp/part-6.img -k arch/arm/boot/zImage
</code>
**/mnt/mmcblk1p1** is where is your rootfs, if it is your live system suppress **INSTALL_MOD_PATH=/mnt/mmcblk1p1**

**/tmp/part-6.img** is your copy of your boot image (part 6 for nvflash, mmcblk0p2 device on eMMC for Linux)

If you want to create a custom version of your kernel's config, run **make menuconfig** after **make paz00_defconfig**.

=== After code update in Gitorious repository ===

<code>
git pull
make menuconfig zImage modules modules_install INSTALL_MOD_PATH=/mnt/mmcblk1p1
abootimg -u /tmp/part-6.img -k arch/arm/boot/zImage
</code>

===== 3.0.x Kernel series =====
TODO

<code>
git clone -b chromeos-ac100-3.0 git://gitorious.org/~marvin24/ac100/marvin24s-kernel.git
cd marvin24s-kernel
</code>

==== Kernel Debugging ====

TODO
   
=== GDB and KGDB ===

TODO

http://kgdb.sourceforge.net

== Remote debugging session ==

TODO

=== SystemTap ===

TODO

[[http://en.wikipedia.org/wiki/SystemTap|Wikipedia's SystemTap article]]

[[http://sourceware.org/systemtap/wiki|SystemTap Wiki]]

http://sourceware.org/systemtap/SystemTap_Beginners_Guide/cross-compiling.html

http://sourceware.org/systemtap/SystemTap_Beginners_Guide/using-usage.html

http://omappedia.org/wiki/Systemtap

[[http://www.redbooks.ibm.com/redpapers/pdfs/redp4469.pdf|SystemTap: Instrumenting the Linux Kernel for Analyzing Performance and Functional Problems]] by IBM

[[http://sourceware.org/systemtap/langref.pdf|Language reference]]

[[http://www.ibm.com/developerworks/linux/library/l-systemtap/index.html|Linux introspection and SystemTap, An interface and language for dynamic kernel analysis]] by [[http://www.ibm.com/developerworks/linux/library/l-systemtap/index.html|M. Tim Jones]]

[[http://dtrace.org/blogs/brendan/2011/10/15/using-systemtap/|Using SystemTap]] by [[http://dtrace.org/blogs/brendan/about/|Brendan Gregg]]

[[http://sprocket.io/blog/2007/11/systemtap-its-like-dtrace-for-linux-yo/|SystemTap: It's like dtrace for linux, yo.]] by [[http://sprocket.io/blog/contact/|Thomas Strömberg]]

[[http://sourceware.org/systemtap/examples/|SystemTap Examples]]

Examples written by Paul Fertser for tracking [[hardware_specs?&#keyboard_touch_led_battery_controller|NVEC]] activities (this assumes you're crosscompiling and then manually scp'ing and staprun'ing modules) :

- first, fetch the address of NVEC:
<code>
stap -B CROSS_COMPILE=arm-none-linux-gnueabi- -a arm -r ~/openmoko/l/ -v -e 'probe 
                     kernel.function("nvec_write_async") { printf("hi, nvecs address is %p\n", $nvec) exit() }'
</code>
**hi, nvecs address is 0xdf8ae000**

- second, with this address, issue events for controlling sound amplifier (warning, guru mode allows arbitrary C code, you can crash a running system with that):
<code>
stap -g -B CROSS_COMPILE=arm-none-linux-gnueabi- -a arm -r ~/openmoko/l/ -v -e '%{ #include 
                     <../drivers/staging/nvec/nvec.h> %} probe begin { %{ nvec_write_async((struct nvec_chip*)0xdf8ae000, 
                     "\x0d\x10\x59\x94", 4) %} exit() }'

</code>
**\x0d\x10\x59\x94** mutes the amplifier, with **\x0d\x10\x59\x95** unmutes it.

=== DTrace ===

TODO

[[http://dtrace.org/|DTrace's blog]]

[[http://www.dtracebook.com/|the DTrace book of scripts and strategy, 1100 pages (2011)]]

[[http://www.crisp.demon.co.uk/blog/index.html|Porting effort of DTrace on Linux]] blog of Paul FOX.

[[http://sourceware.org/systemtap/wiki/SystemtapDtraceComparison|SystemTap vs. DTrace]]

=== ftrace ===

TODO

[[http://lwn.net/Articles/365835/|Debugging the kernel using Ftrace - part 1]]

[[http://lwn.net/Articles/366796/|Debugging the kernel using Ftrace - part 2]]

[[https://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf|Ftrace Linux Kernel Tracing]] by Steve Rostedt
===== Git-Fu =====
TODO

[[http://www.eecs.harvard.edu/~cduan/technical/git/|A tutorial on Git]] by Charles Duan.

[[http://schacon.github.com/git/gittutorial.html|official Git tutorial]]

====== Kernel Hot patching ======

[[http://www.ksplice.com/doc/ksplice.pdf|Ksplice paper]]

[[http://en.wikipedia.org/wiki/Ksplice|Wikipedia's article]]

[[https://wiki.ubuntu.com/Ksplice|Ubuntu's Ksplice]]

[[http://and-developers.com/custom_recovery:alternative_methods#ksplice_attack|ksplice Attack]]
====== Support ======

[[https://lists.launchpad.net/ac100/|Mailing list]]

[[irc://irc.freenode.net/#ac100|channel #ac100 on irc.freenode.net]]