zelea2

How to compile your own Android kernel in linux

4 posts in this topic

First you need an original boot.img file. Extract its components

with the abootimg program.

$ abootimg -x boot.img

writing boot image config in bootimg.cfg

extracting kernel in zImage

extracting ramdisk in initrd.img

Search for the first "1F 8B 08" bytes in zImage (that's the

signature of a gzip file); make a new file starting from there

and gunzip it. This will create your Image kernel (decompressed)

In the new file search again "1F 8B 08" and make a new file out

of that and gunzip it. This will be your kernel config file.

Alternatively you can do 'zcat /proc/config.gz' on your runnig

phone to achieve the same result. For convinience I've already

edited out the CONFIG_ACER_SECURE_MOUNT define and you can

grab the file here.

Install your ARM cross-compiler and toolchain from your favorite place.

grab the kernel sources opensrc_Acer_AV051_S500_RV04RC09_WW_GEN1-20130322.tar.gz

or newer; untargz them. Edit the file ./drivers/gpu/msm/adreno.c and change

in function adreno_iommu_setstate the 'unsigned int link[250];' to 240

otherwise you'll have a frame overflow error.

Also in scripts/Makefile.lib change this line (if you want)

-cmd_gzip = (cat $(filter-out FORCE,$^) | gzip -n -f -9 > $@) || \

+cmd_gzip = (cat $(filter-out FORCE,$^) | 7z a $@ -tgzip -mx=9 -si) || \

because the 7z can also make gzip files but with much better compression.

Finally after you've copied the '.config' in the kernel tree

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- zImage

... and wait. After a while you'll have yout new zImage file.

Now the ramdisk: make a 'work' directory and cd to it.

$ zcat ../initrd.img | cpio -i

edit the default.prop file to 'ro.secure=0' and 'ro.debuggable=1'

and then convert back to compressed cpio:

$ find . ! -name "." | cpio -o -H newc | 7z a ../initrd.img -tgzip -mx=9 -si

now 'cd ..' and put everything back together

$ abootimg --create boot.img -k zImage -r initrd.img

look at the new size of your boot.img modify in bootimg.cfg the bootsize

value (in hex) to reflect this new size and run again with the -f parameter

$ abootimg --create boot.img -f bootimg.cfg -k zImage -r initrd.img

Done. Here is my compiled version.

Edited by zelea2
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So this is a kernel ? Mount RW/RO works with this kernel ? What this kernel contains ? What gouvernors? And what did you modified ?

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Thanks for your tutorial zelea2!! It helped me a lot with building my own kernel. I did a few things in an alternative way:

In adb shell on the device I did:

cat /proc/config.gz > /external_sd/config.gz
Then in shell I did:
adb pull /external_sd/config.gz[/code]


to transfer the file to the current directory. Then I did a 
[code]gunzip config.gz[/code]
to unzip the config file. After modifying the config file (just modified the CONFIG_ACER_SECURE_MOUNT from n to y) I build the kernel. I did not modify anything else!! I did get an error while repacking the ramdisk when using your command. To succesfully repack I used
[code]find . | cpio -o -H newc | gzip > ../initrd.img[/code]
After creating a boot.img it runs perfectly. I get the same benchmark results with my own compiled kernel as with the original (even slightly better!) What do you mean with the frame overflow buffer? Without modification my kernel seems to run fine or am I missing something? Do you also know how I can make the S500 let accept a
[CODE]adb remount[/code]

command?

Thanks in advance!

Edited by bobbes
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Would it be unwise to change other stuff in the build.prop? I'm thinking things like lcd density ( value up or down?),

acer shell, ...

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