Is there any C library for FreeBSD that emulates GNU \ Linux system calls, something like syscall wrapper? I am trying to port my library to FreeBSD and it's very insidiously when my program has been compiled without errors but system calls make a little bit other things than I expected.
For the other way around there is libbsd project.
As for Linux compatibility on FreeBSD, it has Linux ABI support layer called Linuxulator. You might be able to brand your app as Linux one, so it would be ran under Linuxulator.