In order to get core to cross-compile and link successfully (w/ no_std and no_main) it is required that you cross-compile libcore and copy the cross-compiled libs to your rustc sysroot AND xargo must be used. Directions for this process can be found here:

https://github.com/japaric/rust-cross#rust-cross

load virtio 0 0x40200000 /hypervisor.elf && bootelf