An oft-overlooked pain point is that when interacting with C interfaces, it's not good enough to implement a C ABI FFI. There's a world of software out there where the supporrted interface is a C API, at the source level. Compatibility across different versions, or across different implementations, is assured only to programs which interact with the interfaces in ways that correspond particular C source patterns.

The biggest culprit I've met on this front is the POSIX stat family of functions.