http://www.perlmonks.org?node_id=818427


in reply to Re: native exit codes 512 and 2304
in thread native exit codes 512 and 2304

It's only a my guess: on different runtime error like 'malloc() failed' or any different like 'label not found' the error code may be different?
Anyway, the CORE::GLOBAL::exit is redefined and there is no CORE::exit() on the FCGI::* sources.