malloc free sizeof

How do I implement a simple mallow, free, and widely in ask x86?
How does free know how much to actually free?

>>2
aww ok so it basically makes itself a footer or header with info needed

Ty

Im guessing a simple malloc loops through the heap from the first known free address and looks for a spot with enough free space then.

Free would just make everything \0 in the old mallocd space

Correct?