It is not entirely missing that idea, since what you malloc() must be aware of its own size, even if that’s not usually something you get access to as a program

It is not entirely missing that idea, since what you malloc() must be aware of its own size, even if that’s not usually something you get access to as a programmer. One way I’ve seen this done is you malloc() 30 bytes, it allocates 34 and gives you a pointer to 4, and bytes 0-3 hold internal information for the malloc/free implementation.