[U-Boot] standalone apps and their use of exported functions

Hey there!

I am trying to customize/extend uboot with a standalone application which is automatically loaded before booting the kernel. Is there any way i can safely access uboot functions besides the exported(include/exports.h) ones? e.g. functions that can be executed from the command line - like nand copy, saveenv,...

...Im really doing hard on finding some documentation about this subject.

thanks, Valentin