Free Pascal provides a unit that allows you to trace allocation and deallocation of heap memory: heaptrc.
If you specify the -gh switch on the command-line, or if you include heaptrc as the first unit in your uses clause, the memory manager will trace what is allocated and deallocated, and on exit of your program, a summary will be sent to standard output.
More information on using the heaptrc mechanism can be found in the Users guide and Unit reference.