Core News Alert: Ask HN: What's the best resource for learning modern x64 assembly?

Ask HN: What's the best resource for learning modern x64 assembly?
476 by ssklash | 107 comments on Hacker News.
I've found lots of resources for x86, but considerably less for x64. Pentester Academy has a promising course on it, along with shellcoding, but I'm not sure what else is out there.