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C's ABI is that much simpler because it doesn't really place any constraints on the memory layout of your types. With C++ (and others), the values passed around

C's ABI is that much simpler because it doesn't really place any constraints on the memory layout of your types. With C++ (and others), the values passed around may also have vtables linked to them, so your language must then also provide an in-memory representation of objects which is compatible with the C++ representation in order to do FFI method calls. That places quite a constraint on your language because to do it efficiently you basically want a copy of the C++ object model. So you're developing a kind of C++ sibling language, and C++ is quite complex, and now any other languages which want to interoperate with yours has to do the same. This is why it's pretty standard to just have a C FFI and provide a C wrapper for C++ libraries to use them with other languages.

jenadine 4y ago
Of course the C ABI places constraints on the memory layout of the types. For example, alignment. Also in what register "small" types are passed when passing them to functions. It actually depends if the struct has float members or not. C itself is quite complex already. C++ adds more features. But for example, the Rust ABI uses the C++ ABI, because C is too simple and doesn't support unwinding (for panics) or 128bit integers