Run the emulation with:
  
    qemu-system-sparc64 -M sun4u -kernel output/images/vmlinux -append "root=/dev/sda console=ttyS0,115200" -serial stdio -drive file=output/images/rootfs.ext2,format=raw -net nic,model=e1000 -net user
  
  The login prompt will appear in the terminal that started Qemu.
  
  Tested with QEMU 2.5.0