The kernel requires a root file system because when it finishes initializing itself it will look for userland and the user applications. With an embedded system is there is no partitioning and the kernel will need to be made aware of the location of that root file system. This is done by plugging it into the linker map, turn the root file system, use the binary tools to convert it into a .o file, which can be added into the linker map of the final kernel. Define a .ram disk section and drop "rootfs", the image, convert it into a binary file into the linker map. Add symbols around ramdisk, for example ramdisk_begin and ramdisk_end, to allow the kernel to find ramdisk at boot time.