I use Grub to dual boot using rEFInd.
Procedure-
1. Check that Grub is installed/install it.
2. Then I used the Arch wiki to install Grub for Uefi systems
Code:
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=Slackware --recheck
(ESP is mounted at /boot/efi)
http://wiki.archlinux.org/index.php/Grub#UEFI_systems_2
You may also want to look at the following if you use Grub with Slackware:
https://www.linuxquestions.org/quest...ml#post5078462 so that an initrd is attached only with the generic kernel and not with the huge kernel.