[emilfihlman]

Can you post a definite source supporting this?

[luke0016]

There isn't one, because it's wrong.

Source: run strace on almost any useful Linux command (e.g. ls, sort, which, ...), you'll see it makes calls to both brk() and mmap().

[toast0]

The OP admitted it was wrong, but just because everyone does it doesn't mean it's not undefined behavior.