Conversely, I don't think `malloc` et al. say anything about a "heap". All they promise is they'll allocate some memory, with certain size/alignment and lifetim

Conversely, I don't think `malloc` et al. say anything about a "heap". All they promise is they'll allocate some memory, with certain size/alignment and lifetime guarantees. It's up to the platform to figure out how to fulfill those guarantees.