DOWNLOAD THE KERNEL SOURCE CODE
First we download the kernel source code from
https://android.googlesource.com
Within that page there are kernels for other platforms too. We choose to download
kernel/goldfish project from there.
$ git clone https://android.googlesource.com/kernel/goldfish
A goldfish directory appears:
$ cd goldfish
This directory does not contain any source code in it.
We check which branch we have downloaded:
$ git branch
it shows * master , not the one we are searching for:
To
list all
remote available
branches:
$ git branch -r
or
$ git remote show origin
origin/HEAD -> origin/master
origin/android-goldfish-2.6.29
origin/android-goldfish-3.4
origin/linux-goldfish-3.0-wip
origin/master
What does goldfish mean? (from android-kernel mail list)
Goldfish is the kernel hacked branch that supports the qemu based arm emulator for android, so it is the one we need.
Download GOLDFISH kernel version
Choose the version that suits you.
$ git checkout --track -b android-goldfish-2.6.29 origin/android-goldfish-2.6.29
$ git branch
* android-goldfish-2.6.29
master
RUNNING THE EMULATOR
Within this link we will find how to get the android emulator, and launch it.
Building Android in Debian Sid
Showing the kernel version running in the emulator
$ adb shell
# cat /proc/version
Linux version 2.6.29-00261-g0097074 (digit@digit.mtv.corp.google.com) (gcc version 4.4.0 (GCC) ) #14 Tue Feb 2 15:49:02 PST 2010
OBTAINING KERNEL CONFIGURATION
We are going to
obtain the kernel configuration
.config file
from within
our running emulator.
$ cd /path/to/goldfish # we enter in the kernel source directory.
$ adb pull /proc/config.gz . # get compressed .config file from the emulator.
$ gunzip config.gz # uncompress it.
$ cp config .config # rename it into .config
Now you can edit .config file the way it suits you the most.
BUILDING AND COMPILING THE KERNEL
CROSS_COMPILE environment variable stores the path to the
arm cross compiling toolchain. I use the one which comes with android source code.
$ ARCH=arm CROSS_COMPILE=/path/to/mydroid/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi- make
Executing
make will build the kernel.
Last lines will show:
Kernel: arch/arm/boot/Image is ready
Kernel: arch/arm/boot/zImage is ready
So we have obtained
Image and
zImage kernel binary files.
RUN THE EMULATOR USING THE NEW COMPILED KERNEL IMAGE
We need
-kernel option:
$ emulator -kernel /path/to/goldfish/arch/arm/boot/zImage -show-kernel -verbose
We can check now the kernel version:
$ adb shell
# cat /proc/version
Linux version 2.6.29-00262-gb0d93fb (user@myPC) (gcc version 4.4.0 (GCC) ) #1 Sun May 2 14:27:31 CEST 2010
If we do not specify kernel option it usually uses the prebuilt one:
$ emulator -show-kernel -verbose
emulator: argv[01] = "-kernel"
emulator: argv[02] = "/path/to/mydroid/prebuilt/android-arm/kernel/kernel-qemu"
ACTIVATING MODULE LOADING SUPPORT IN THE KERNEL
Module loading support is previously disabled in the kernel, if we want to load modules in the kernel we have to enable it:
edit .config file and set:
CONFIG_MODULES=y
$ ARCH=arm CROSS_COMPILE=/path/to/mydroid/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi- make
I am asked about some options when executing make. I ask yes for module related options.
After compiling I see several modules have been built.
MODPOST 6 modules
CC drivers/video/fb_sys_fops.mod.o
LD [M] drivers/video/fb_sys_fops.ko
CC drivers/video/syscopyarea.mod.o
LD [M] drivers/video/syscopyarea.ko
CC drivers/video/sysfillrect.mod.o
LD [M] drivers/video/sysfillrect.ko
CC drivers/video/sysimgblt.mod.o
LD [M] drivers/video/sysimgblt.ko
CC drivers/video/vfb.mod.o
LD [M] drivers/video/vfb.ko
We can
upload the
modules in the emulator
and install them:
$ adb push drivers/video/fb_sys_fops.ko /data
$ adb shell
# insmod /data/fb_sys_fops.ko
REFERENCE
http://www.cianer.com/androidg1/28-building-android-kernel-images
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