There is no documentation about this within the U-Boot source code
but you should be able to find something on the interwebs.
+config CMD_ZBOOT
+ bool "zboot - x86 boot command"
+ help
+ With x86 machines it is common to boot a bzImage file which
+ contains both a kernel and a setup.bin file. The latter includes
+ configuration information from the dark ages which x86 boards still
+ need to pick things out of.
+
+ Consider using FIT in preference to this since it supports directly
+ booting both 32- and 64-bit kernels, as well as secure boot.
+ Documentation is available in doc/uImage.FIT/x86-fit-boot.txt
+
endmenu
menu "Environment commands"
* Command line configuration.
*/
-#define CONFIG_CMD_ZBOOT
-
#define CONFIG_BOOTARGS \
"root=/dev/sdb3 init=/sbin/init rootwait ro"
#define CONFIG_BOOTCOMMAND \