I need to find a specific function, where to look?

[Andru]

I just find it strange that the function could not be found anywhere in fpc units, not even in macosall.pp

Unfortunately this is not strange... there is no libc unit for Linux/MacOS X/*BSD, where must be a lot of functions.

Yes, adding the cdecl fixed it, thanks!

Only cdecl? Although, maybe somewhere your application has been already linked to libc.