[U-Boot] [U-Boot-Users] standalone code

Hello,

I want to use the u-boot drivers such as gpio and spi on a standalone application. What do I need to modify in the Makefile to build and link my code with the rest of the U-boot code in order to include those drivers in my application? because when I try to compile my code, it shows some errors of undefined references. Is it possible to run that application automatically when the u-boot starts? maybe from the SD card?

Thanks.Diego Preciado