I implemented the kexec for Linux 2.4.x/arm based on the bootloader of OpenBSD.
It can be used to boot another kernel(such as 2.6.x) within the 2.4.x kernel, and it is useful for somebody who want to test the 2.6.x kernel without flush the flash.
Not very security. I have ever corrupted my jffs2 root file system on nand flash with this. Turn off the MTD support on booted kernel.
make KERNEL_SRC=<some place>
copy vmlinux to the directory of kexec.
Hope helpful for somebody.