According to the Debian arm64 build daemon build log, a hugo -s docs would fail with "function not implemented" error:

# TODO: Add "hugo-docs" package in the future
obj-aarch64-linux-gnu/bin/hugo -s docs -d public/html --uglyURLs
2016/01/12 00:33:24 function not implemented
debian/rules:9: recipe for target 'override_dh_auto_build' failed

Initial code search on "function not implemented" led me to golang.org/x/sys/unix, Errno 38 or 0x26, i.e., ENOSYS.

I was able to reproduce this on Debian arm64 developer machine asachi.debian.org, and it is not one single "function not implemented" errors, but random amount of it, from 9 errors to 94812 errors. I'll need more time to investigate.

Note that this problem does not affect armhf and armel platforms.