U-Boot uses Flat Image Tree (FIT) as a standard file format for packaging images that it reads and boots. Documentation about FIT is available at doc/uImage.FIT
U-Boot also provides binman for cases not covered by FIT. Examples include initial execution (since FIT itself does not have an executable header) and dealing with device boundaries, such as the read-only/read-write separation in SPI flash.
.. toctree:: :maxdepth: 2 binman