Table of Contents
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
Kernels cooked by Jani Monoses
http://launchpadlibrarian.net/89568135/linux-image-3.0.8-4-ac100_3.0.8-4.3_armel.deb
Debian
Fedora
http://dmarlin.fedorapeople.org/yum/f15/arm/os/Packages/kernel-tegra-2.6.40.3-2.09.fc15.armv7hl.rpm
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
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
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
TODO
GDB and KGDB
Remote debugging session
TODO
SystemTap
TODO
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
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
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
TODO
the DTrace book of scripts and strategy, 1100 pages (2011)
Porting effort of DTrace on Linux blog of Paul FOX.
ftrace
TODO
Debugging the kernel using Ftrace - part 1
Debugging the kernel using Ftrace - part 2
Ftrace Linux Kernel Tracing by Steve Rostedt