amd64-5.0_BETA MULTIBOOT not working

[Juraj Hercek <nbsd%hck.sk@localhost>]

Hello,

I've been messing around with kernels and I've noticed I cannot 
`multiboot' netbsd kernel. Steps done:

1) installed grub2 which should be able to boot 64bit kernels via 
multiboot protocol
2) started GENERIC via grub2, but it ended up in reboot
3) manually installed native NetBSD bootloader (installboot didn't work, 
had to use dd - not sure why...)
4) started GENERIC via native NetBSD bootloader's boot command, booted ok
5) started GENERIC via native NetBSD bootloader's multiboot command, 
ended up in reboot
6) compiled new kernel based on GENERIC with `options MULTIBOOT' enabled
7) started new kernel via native NetBSD bootloader's boot command, booted ok
8) started new kernel via native NetBSD bootloader's multiboot command, 
ended up in reboot
9) started new kernel via grub2, ended up in reboot

Is multiboot expected to be working on amd64?
Should I file PR?

Thanks,
Juraj

PS: I didn't find relevant PR, only multiboot related ones are 
port-i386/38356 and port-i386/38603
PPS: When executing step (8), I've seen couple of kernel boot lines, but 
it was too quick to catch it