[TUTORIAL] Modifying the boot image

[Molle]

Here's a short tutorial on how to modify the boot image of an X7 in order to e.g. edit the Mali GPU related speed parameters. The process relies heavily on Finless Bob's prior work (http://freaktab.com/forum/developmen...8998#post28998).

The following external tools are needed:

• imgRePackerRK_106.zip (https://forum.xda-developers.com/sho....php?t=2257331)
• rkcrc: (https://github.com/naobsd/rkutils)

The process is as follows. Note: I have simplified the commands by omitting long path names etc. Use your own judgement on how to apply in your own environment.


Unpack the ROM image

$ imgrepackerrk wasser-3.0.6-minix-x7-rk3188.img

Strip the 8 byte header from the extracted boot image

$ dd if=boot.img.krnl of=bootimg.cpio.gz skip=8 bs=1 count=20000000

The result is a gzipped cpio archive file.


Extract the cpio archive to a directory

$ mkdir newboot
$ cd newboot
$ gzip -dc ../bootimg.cpio.gz | cpio -iduvm

Gzip will complain about trailing garbage. That's the footer, which can be ignored.


Edit the files as needed.

Note: I'm using the Mali patch as an example. Pay attention to the path to the module. It may vary between Android versions.

Open file 'init.rk30board.rc' with a text editor, find the line containing the entry for the 'mali.ko' kernel module and edit it to look as follows:

insmod /system/lib/modules/mali.ko mali_dvfs=133,200,266,300,400,600,798 mali_init_clock=133

Recreate the raw boot image file

Boot images can not contain touched/modified files, so the dates of the edited files need to be reset. In the new Lollipop ROM there's a symbolic link inside the boot image which will trigger an error but it shouldn't cause any problems.

$ find . -exec touch -d "1970-01-01 01:00" {} \;

Then just repack the files to a new gzipped cpio archive.

$ find . ! -name "." | sort | cpio -oa -H newc | gzip -n > ../newboot.cpio.gz
$ cd ..

Add CRC to the file to create the final image file

Note: You need to have a version of the rkcrc utility which supports the -k parameter.

$ rkcrc -k newboot.cpio.gz newboot.img

FINAL NOTE: Before attempting to flash the new boot image, you might want to do the following checks:

1. Is the size of the new boot image file within ballpark of the unmodified one?
2. Can it be taken apart with this process?

[Molle]

Reserved.

[Pluto]

Thanks a lot Molle.


It took me a bloody day to find "rkutils", the linked website (linux-rockchip.info) seems to have trouble.

Anyways, so far "bash for windows" has done quite a good job with the basic command, and i finally found a windows version of the rkcrc (really happy i didnt compile).. However, i am stuck at the "insmod" right after i extract the cpio package.

root@XXXX:/mnt/c/Users/XXXXXXX/Desktop/cpio# gzip -dc bootimg.cpio.gz | cpio -iduvm
charger
data
default.prop
dev
drmboot.ko
file_contexts
fstab.rk30board.bootmode.emmc
fstab.rk30board.bootmode.unknown
init
init.box.samba.rc
init.connectivity.rc
init.customer.rc
init.environ.rc
init.initd.rc
init.rc
init.rk30board.bootmode.emmc.rc
init.rk30board.bootmode.unknown.rc
init.rk30board.environment.rc
init.rk30board.rc
init.rk30board.usb.rc
init.rockchip.rc
init.su.rc
init.trace.rc
init.usb.rc
init.zygote32.rc
proc
property_contexts
res
res/images
res/images/charger
res/images/charger/battery_0.png
res/images/charger/battery_1.png
res/images/charger/battery_2.png
res/images/charger/battery_3.png
res/images/charger/battery_4.png
res/images/charger/battery_5.png
res/images/charger/battery_charge.png
res/images/charger/battery_fail.png
res/images/charger/capacity_text_bottom.png
res/images/charger/capacity_text_left.png
res/images/charger/capacity_text_right.png
res/images/charger/capacity_text_top.png
rk30xxnand_ko.ko
sbin
sbin/adbd
sbin/e2fsck
sbin/healthd
sbin/mkdosfs
sbin/resize2fs
sbin/sdtool
sbin/ueventd
sbin/watchdogd
seapp_contexts
selinux_version

gzip: bootimg.cpio.gz: decompression OK, trailing garbage ignored
sepolicy
service_contexts
sys
system
ueventd.rc
ueventd.rk30board.rc
4878 blocks

so, whenever i input "insmod /system/lib/modules/mali.ko mali_dvfs=133,200,266,300,400,600,798 mali_init_clock=133", would get a

root@XXX:/mnt/c/Users/XXXX/Desktop/cpio# insmod /system/lib/modules/mali.ko mali_dvfs=133,2
ali_init_clock=133
insmod: ERROR: could not load module /system/lib/modules/mali.ko: No such file or directory

obviously that was expected as i noticed before hand that those folders should be empty, as i extracted a 1.42mb package.

Any clue what i am doing wrong? (Apart from using linux under windows).

EDIT: forget it, didnt see that i should add the line to that specific file in the beginning.

[Molle]

i should add the line to that specific file in the beginning.

There is an existing 'insmod' line for the Mali kernel module in 'init.rk30board.rc'. Just append the parameter part of my example line to that and you should be ok.

[Pluto]

Yup, found out the hard way.

Nevertheless, i've failed.

Initially, gzip -dc together with cpio would'nt work well, and i noticed a few files being unreadable.

gzip -d works, and i got a lot less issues without it, but cpio command wouldnt respond to it at all, the cpio file however could be extracted with 7zip on windows (this is where my doubts are).

I edit the line on the .co file, did the time trick, repack and crc signing. All i get is the blue led in the front, no HDMI output at all.

[Molle]

root@XXXX:/mnt/c/Users/XXXXXXX/Desktop/cpio# gzip -dc bootimg.cpio.gz | cpio -iduvm

Looking at the command you executed, it seems you extracted the files to the same directory where the gz file resided. If you didn't delete it afterwards, you probably packed it inside the new boot image. I have put some extra instructions to the original post on how to unpack the files to a separate directoty.

[Pluto]

That is exactly where i usually mess up with such cases, paths.

I just redid it, the image file differ slightly. I will flash in a couple of hours and report back.

PS, what is the address for flashing a boot file in our usual tools?