[U-Boot] Sections of RAM used by u boot

Hi All, I am attempting to run a standalone program on an ARM with u boot.Currently at the stage of running the hello world application. I would like to use a lot of the available RAM in the stand alone program i plan to write. It is unclear to me which parts of the RAM are used by u boot and i dont want to corrupt data. Is there any clear list or variable that holds the location of RAM used or can i force only a certain section of ram to be used by uboot. I have already noticed the center of the RAM is modified when any action occurs on the SD card if this is already documented or answered in another post i have been unable to find it with a search so feel free to point me toward any info. Thanks