If you follow the upgrade instructions in my 5.8 update post, there is one ‘gotcha’. If your copy of /usr/src was downloaded using “make src-create-shallow”, you will not have any git history – or any branches other than 5.6.
The easy, cheesy way to fix it is to remove /usr/src, then type “make src-create” in /usr, and proceed from there. There’s probably a way to edit in the other branches, but I haven’t tried it yet. I’m counseling the brute force method for now.