Hi, I'm a maintainer of simple-sendfile and need to implement the following is to rescue 32bit Linux: - If the COff size is 8, the following FFI is used: foreign import ccall unsafe "sendfile64" c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t) - Otherwise, the following FFI is used: foreign import ccall unsafe "sendfile" c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t) How can I implement this? I guess that Setup.hs should evaluate (sizeOf (1 :: COff)) and define a C macro, say LARGE_OFFSET and write the following code. #ifdef LARGE_OFFSET foreign import ccall unsafe "sendfile64" #else foreign import ccall unsafe "sendfile" #endif I have no experience to use Build-Type: other than Simple in cabal files. Would someone explain how to implement it concretely or suggest examples which implement similar things? For more informaion, please read: https://github.com/yesodweb/wai/issues/372 Thanks. --Kazu