Is a Linux executable “compatible” with OS X?

Question

If you compile a program in say, C, on a Linux based platform, then port it to use the MacOS libraries, will it work?

Is the core machine-code that comes from a comp

Answer 1

There is no "core byte-code that comes from a compiler". There is only machine code.

While the same machine instructions may be applicable under several operating systems (as long as they're run on the same hardware), there is much more to a hosted executable than that, and since a compiled and linked native executable for Linux has very different runtime and library requirements from one on BSD or Darwin, you won't be able to run one binary on the other system.

By contrast, Windows binaries can sometimes be executed under Linux, because Linux provides both a binary format loader for Windows's PE format, as well as an extensive API implementation (Wine). In principle this idea can be used on other platforms as well, but I'm not aware of anyone having written this for Linux<->Darwin. If you already have the source code, and it compiles in Linux, then you have a good chance of it also compiling under MacOS (modulo UI components, of course).