[vasama]

Looks more like an implementation of undefined behaviour to me.

[dang]

"Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

https://news.ycombinator.com/newsguidelines.html

[monocasa]

The underlying implementations define the behavior here very well.

[fanf2]

Well, I would not go that far. My coroutine hack relies on “unwarranted chumminess with the implementation” (http://c-faq.com/struct/structhack.html) and there are lots of incidental things that can break it. It is best treated as an example of the principles of thread switching and stack allocation.