Hi, recently during a ghcup release, we stumbled over yet another `ccall` bug on Darwin: https://github.com/biegunka/terminal-size/pull/16 This took Ben some time to debug (thanks again) and it isn't always clear with such bugs whether something is wrong with GHC/RTS/GC or a library, so this can be a time-sink. It's also not the first time it happened: * https://github.com/haskell/unix/pull/110#issuecomment-613384845 * https://github.com/hasufell/hpath/commit/74d686547e67da3eeae327c84c63f838332... I can't say that I fully understood what the exact difference here is and why it seems to matter much more on Darwin than on other systems. So I think it would be helpful if we could come up with: 1. a clear description of the differences of ccall vs capi 2. an explanation why ccall can lead to terrible bugs on darwin 3. a guideline of when using one over the other is appropriate Not everyone deals with ffi on a regular basis, so I hope the experts here can shed some light! Cheers, Julian