In the general case it's not necessarily trivial, just like porting software from x86 linux to x86 mac is not necessarily trivial. For example your software might rely on some system interface that's done differently on those platforms, e.g. if you're using kprobes then it would take an effort to port that to use dtrace. And if we're talking about a GUI application then the framework it uses might not be first-class on mac, e.g. GTK only works in an X11-based way. But there are cases where it's as simple as pushing the compile button and getting out something working.