Regarding building NOVA kernel

Hi, I have tried to build NOVA kernel but I am getting error..... genode-main@lists.sourceforge.net spawn qemu-system-x86_64 -no-kvm -display sdl -cpu core2duo -serial mon:stdio -m 512 -cdrom var/run/demo.iso -cdrom var/run/demo.iso -cdrom var/run/demo.iso qemu-system-x86_64: -display sdl: SDL support is disabled Aborting, received EOF Log step failed, retry. Boot process failed 3 times in series. I give up! make: *** [run/demo] Error 255

I have tried to comment -display sdl in build.conf but i didn't get any output. Please provide solution.