I created a setup of a guest virtual machine High Sierra which runs by VirtualBox.
I KDP on both guest and host. I copied the development version of XNU from the KDP directory into the kernel directory on both guest and host.
I read that VirtualBox does not have the implementation for NVRAM so I had to use the following command to setup the kernel boot arguments for kernel debugging.
VBoxManage setextradata “your virtual machine name>" "VBoxInternal2/EfiBootArgs" [here go the kernel boot arguments]
However, I tried the combination of Command+Option+Control+Shift+Esc however it does not work.