(bad acting) NIFs. Thankfully you can mark 'em as the dirty evil little things that they are (with negligible overhead):
As a side issue, is there an easy method to determine if a NIF is problematic in this regard? I've used jiffy[0] in several codebases, but I keep reading these warnings and wondering whether I should be doing so.
The warnings are mostly about NIFs you write yourself, which you typically
avoid if possible. And jiffy itself goes quite a long way to cooperate with
Erlang VM's internals (at least so I've heard).
[0] https://github.com/davisp/jiffy