The Xilinx Git repositories, U-Boot are tagged for the release with a tag of xilinx-v2018.3 and Linux with tag of xlnx_rebase_v4.14_2018.3.
FSBL The First Stage Boot Loader (FSBL) used to generate the boot.bin file is based on the 2018.3 release of the Xilinx tools.
The release is based on a v2018.01 U-Boot created from the xilinx-v2018.3 tag. More details about configuring, building and running U-Boot are located on the U-Boot and Build U-Boot pages.
Linux The release is based on a 4.14 Linux kernel created from the xilinx-v2018.3 tag. More details about configuring, building and running Linux are located on the Linux, Zynq Linux and Build Kernel pages.