Setup the cross compiling environment

The one I used is Sourcery CodeBench Lite Edition, you can get it from its website.
Please choose the eabi verison and the tar.bz2 one. I used arm-2008q3-72-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
Untar the file:

$ mkdir ~/overo-standalone
$ cd ~/overo-standalone
$ tar xvjf arm-2008q3-72-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2

Add the bin to your PATH:

$ export PATH=$PATH:~/overo-standalone/arm-2008q3/bin

Write the program

The following two Hello World programs have been tested on an overo.
You can play with them.
Get source files from here.

Compile the program

Assembly verison:

$ cd asm/

Use make to compile the asm program

$ make

C version:

$ cd c/

Run the compile file in c program folder

$ sh compile

Run the program

You needed a flashed, bootable MicroSD. You can make one by using Sakoman's scripts (mkcard.sh and mksdcard.sh).
Copy the .bin file generated by the compiler to the boot drive on the SD card:

$ cp *.bin /media/boot/

Umount the SD card

$ umount /media/boot
$ umount /media/rootfs

Plug the SD card in overo and connect the overo on a Tobi expansion board.
Power it up and go into serial console.

When the console prompt "Hit any key to stop autoboot", please hit any key to interrupt.
And run:

# mmc list
# mmc part
# fatls mmc 0:1
# fatload mmc 0:1 0x80200000 boot.bin
# go 0x80200000

By now you should see "Hello world!" poping in the console.