How to write a kernel module on Android (Sony Ericsson Xperia Arc S)

I wrote and tested the code on my Sony Ericsson Xperia Arc S and it works (in general in should work for any Android phone).

Connecting via adb and USB, and “su” to root, the “lsmod” listed all the kernel module (in general, the article at http://developer.sonyericsson.com/wp/2011/05/06/how-to-build-a-linux-kernel/ gave a very good coverage of what to do in Linux kernel compilation for SonyEricsson phone):

# lsmod
android_module 654 0 - Live 0x7f007000 (P)
sdio 16532 0 - Live 0x7f000000


“android_module” was the one I had inserted via “insmod android_module.ko”.

Here’s how to do it:

First the original program was copied from:

http://rechtzeit.wordpress.com/2011/03/21/77/

Or reproduced as follows:

android_module.c:

#include"linux/module.h"
#include"linux/kernel.h"
//replace the "" with angular brackets
int init_module(void)
{
printk(KERN_INFO "Hello android kernel...\n");
return 0;
}

void cleanup_module(void)
{
printk(KERN_INFO "Goodbye android kernel...\n");
}


And the file “Makefile” is:

obj-m += android_module.o

all:
make -C /home/tteikhua/android/sony_ericsson_src/58/kernel/ M=$(PWD) modules
clean:
make -C /home/tteikhua/android/sony_ericsson_src/58/kernel/ M=$(PWD) clean


The directory where the kernel is located (“-C” above) is where I had downloaded the SonyEricsson kernel image from here:

http://developer.sonyericsson.com/wportal/devworld/downloads/download/30a2181182tarbz2?cc=gb&lc=en

And the following command will use the Makefile from above:

ARCH=arm CROSS_COMPILE=/opt/CodeSourcery/Sourcery_G++_Lite/bin/arm-none-linux-gnueabi- make


As shown above, the cross compiler I had used is from CodeSourcery.

And after “insmod android_module.ko” you can see the debugging message in “dmesg” output:

<6>[11184.063507] Hello android kernel...
<7>[11619.209655] msmrtc_timeremote_set_time: 11/29/2011 10:09:36 (04)
<6>[11619.210418] RPC CALL -- TOD TIME UPDATE: ttick = 404244221
<6>[11619.210418] stamp=52910543933046785, freq = 0
<7>[11619.211578] msmrtc_tod_proc_result: 12/29/2011 10:09:36 (03)
<6>[11619.211578] rs30000048 rs30000048.262144: setting system clock to 2011-12-29 10:09:36 UTC (1325153376)
<6>[11662.112365] device rmnet0 left promiscuous mode
<6>[11662.112579] device rmnet0 entered promiscuous mode
<6>[11669.958221] device rmnet0 left promiscuous mode
<6>[11669.958435] device rmnet0 entered promiscuous mode
<7>[11698.181060] msmrtc_timeremote_set_time: 11/29/2011 10:10:55 (04)
<6>[11698.187622] RPC CALL -- TOD TIME UPDATE: ttick = 406832008
<6>[11698.187652] stamp=52910548228014081, freq = 0
<7>[11698.193939] msmrtc_tod_proc_result: 12/29/2011 10:10:55 (03)
<6>[11698.194030] rs30000048 rs30000048.262144: setting system clock to 2011-12-29 10:10:55 UTC (1325153455)
<6>[11814.442901] bq27520 0-0055: bq27520_handle_soc_worker() capacity=97 (100) flags=0x229 ctrl_status=0x28b soh_state=0x3, valid=1
<6>[11984.057373] Goodbye android kernel...
#


And the “Goodbye” is when “rmmod android_module” is executed. In between are debugging message from other components in the kernel.