DRAFT

Generality

A side note, at the Kernel level soft (armel)/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). Linaro has made a benchmark about this subject.

NVidia's Tegra21), which is dual-core ARM Cortex-A9, supports only VFPv3 2) and not NEON 3) extensions which are more powerful.

As of 2012/06/28, the most stable kernel is 3.0.19. This kernel is based on the original work made by Google. Work has been started on a 3.1.10 kernel for AC100, which is based on the work of NVIDIA. The next Ubuntu version 12.10 will be based upon this kernel. There also exists a very experimental version of a mainline kernel (for-next) with a minimal amount of patches.

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

Debian

Fedora

RedSleeve

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

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

Cross-compiling and native.

2.6.38 Kernel series

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

/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

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

3.0.x Kernel series

TODO

From marvin24s git

To build the kernel native on the ac100, do the following:

git clone -b chromeos-ac100-3.0 git://gitorious.org/~marvin24/ac100/marvin24s-kernel.git
cd marvin24s-kernel
make paz00_defconfig
make zImage modules
make modules_install

You will find the kernel in arch/arm/boot/zImage, which you can flash with abootimg (see above).

Cross-Compiling: If you don't have the time to wait for a build on the AC100 (~ 30 minutes), you can try with a cross-compiler on your favorit desktop machine. How to setup such an environment is out of scope of this article, but google is your friend.

The procedure is similar to the native one:

git clone -b chromeos-ac100-3.0 git://gitorious.org/~marvin24/ac100/marvin24s-kernel.git
cd marvin24s-kernel
make paz00_defconfig ARCH=arm
make zImage modules INSTALL_MOD_PATH=/tmp INSTALL_MOD_STRIP=1 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
make modules_install INSTALL_MOD_PATH=/tmp INSTALL_MOD_STRIP=1 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

The INSTALL_MOD_PATH and INSTALL_MOD_STRIP arguments are optional, but convenient. After this, you will find the stripped modules under /tmp/lib/modules/<kernel-version>.

Similar procedures can be used for the 3.1 and for-next kernels.

Some note on the needed kernel command lines: The 3.0 series uses a reserved video memory which is created by adding “mem=448M@0” to the kernel command line. Later kernels can reserve this memory by themself, thus adding “mem=512M@0” is required here.

The for-next series is very special (you may have guessed that already). First, everything is setup by device-tree info (if you don't know what a device-tree is, yes, google is your friend again). This means that beside the kernel and the modules, you also have to compile the device-tree, which is done by the “dtbs” make target. After that, the compiled device-tree (in arch/arm/boot/tegra20-paz00.dtb) must be concatenated to the kernel image. So something like

cat arch/arm/boot/tegra20-paz00.dtb >> arch/arm/boot/zImage

should be sufficient. Make sure you used paz00_defconfig, because this kernel seems to ignore the parameters submitted by the bootloader.

Stock Ubuntu 12.04 Kernel

Step by step: Recompiling the Ubuntu stock kernel natively (for example to patch it) coming from a stock Ubuntu 12.04 install. As of writing the kernel-version is 3.0.27 and will have to be replaced when another kernel comes out/is used. The created files will be copied to a safe place (/home/turbo/Downloads/ in my case)

Become root for all steps

sudo su

Install dependencies for the kernel and build it:

apt-get build-dep linux-ac100
apt-get install build-essential lzop
cd /usr/src/
apt-get source linux-ac100
cd linux-ac100-3.0.27/

Now if you want the original Ubuntu config do

cp /boot/config-$(uname -r) .config

If you want the standrad ac100 config instead do:

make paz00_defconfig

Apply patches if wanted. In this example I use gordans overclocking patches from his site.

patch -p1 < tegra_common.patch
patch -p1 < tegra_1200.patch

(Note that one patch didn't apply cleanly, but the errors were pretty obvious and easy to fix manually.)

make -j3 INSTALL_MOD_STRIP=1 zImage modules
make -j3 modules_install
cp arm/boot/zImage /home/turbo/Downloads/zImage1200-3.0.27
cp .config /boot/config-3.0.27

Get the bootimg.cfg

cd /boot/bootimg.cfg /home/turbo/Downloads/

Adjust the bootimg.cfg to your needs. Most importantly giving it a cool greeting text of course!

Create the initrd

cp .config /boot/config-3.0.27
update-initramfs -k 3.0.27 -c
cp /boot/initrd.img-3.0.27 /home/turbo/Downloads/initrd1200-3.0.27.img

Create the final image

cd /home/turbo/Downloads/
abootimg --create part6_1200-3.0.27.img -f bootimg.cfg -k zImage1200-3.0.27 -r initrd1200-3.0.27.img

In my case (10K, Android 2.2) the boot partition is partition 6 as seen by nvflash and /dev/mmcblk0p4 as seen from Ubuntu. Make sure you flash to the right partition, this means: `cat /proc/partitions` has to show the partition as 8.0 MiB and `sudo abootimg -i /dev/mmcblk0p4` has to show “Android boot Image” in the first line.

Double-check and create a backup of the boot partition:

dd if=/dev/mmcblk0p4 of=/home/turbo/Downloads/part6-$(uname -r).img

Size of the original is 8388608 aka 8.0M. This backup wont help you if it's on your ac100, so: Be sure to copy this image somewhere else.

Be sure to copy this image somewhere else. Really.

Flash the image

dd if=/home/turbo/Downloads/part6_1200-3.0.27.img of=/dev/mmcblk0p4

Reboot.

3.10.x Kernel series

3.10 build process is close to 3.0 for-next. Device-tree is mandatory, you need to build it and concatenate with a kernel:

make dtbs
cat arch/arm/boot/tegra20-paz00.dtb >> arch/arm/boot/zImage

But 3.10 don't use paz00_defconfig anymore. Instead is uses tegra_defconfig (main idea of device-tree is to have all-in-one kernel and choose drivers on boot time using device-tree):

make tegra_defconfig

Mainline Git Kernel

From 3.15, AC100 finally boots the official mainline kernel ! To succesfully cross-compile it, i used linaro precompiled toolchain http://releases.linaro.org/14.05/components/toolchain/binaries/gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux.tar.xz:

wget http://releases.linaro.org/14.05/components/toolchain/binaries/gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux.tar.xz

extract it somewhere, and export install path so the toolchain can be found:

tar xvf gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux.tar.xz 
export PATH=$PATH:gcc-linaro-arm-linux-gnueabihf-4.9-2014.05_linux/bin/

Now you have to clone the kernel git repository:

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
cd linux

As already described above, configure && make && install and your kernel is ready!

make tegra_defconfig ARCH=arm
make zImage modules dtbs INSTALL_MOD_PATH=/tmp INSTALL_MOD_STRIP=1 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
make modules_install INSTALL_MOD_PATH=/tmp INSTALL_MOD_STRIP=1 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-

Copy everything you need in a folder (to copy on SD or USB key and put into AC100)

mkdir ~/linux-3.16-0
mv /tmp/lib/ ~/linux-3.16-0/
cp arch/arm/boot/zImage ~/linux-3.16-0/
cp arch/arm/boot/dts/tegra20-paz00.dtb ~/linux-3.16-0/

Kernel Debugging

GDB and KGDB

Remote debugging session

TODO

SystemTap

TODO

Wikipedia's SystemTap article

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

SystemTap: Instrumenting the Linux Kernel for Analyzing Performance and Functional Problems by IBM

Language reference

Linux introspection and SystemTap, An interface and language for dynamic kernel analysis by M. Tim Jones

Using SystemTap by Brendan Gregg

SystemTap: It's like dtrace for linux, yo. by Thomas Strömberg

SystemTap Examples

Examples written by Paul Fertser for tracking NVEC activities (this assumes you're crosscompiling and then manually scp'ing and staprun'ing modules) :

- first, fetch the address of NVEC:

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() }'

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):

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() }'

\x0d\x10\x59\x94 mutes the amplifier, with \x0d\x10\x59\x95 unmutes it.

DTrace

ftrace

Git-Fu

Kernel Hot patching

Support

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