Devel::leak has two functions: notesv and checksv.

notesv walks the perl internal table of allocated svs (scalar values) - (which actually contains arrays and hashes too), and records their addresses in a table. it returns a count of these "things", and stores a pointer to the table (which is obtained from the heap using malloc()) in its argument.

checksv is passed argument which holds a pointer to a table created by notesv. it re-walks the perl-internals and calls sv_dump() for any "things" which did not exist when notesv was called. it returns a count of the number of "things" now allocated.