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How to compile your own Android kernel in linux

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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, 30 May 2013 - 02:37 PM.

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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
to transfer the file to the current directory. Then I did a
gunzip config.gz
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
find . | cpio -o -H newc | gzip > ../initrd.img

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
adb remount

Thanks in advance!

Edited by bobbes, 17 June 2013 - 07:31 PM.

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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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