I spent some time hacking around on this from a library perspective when I had to interoperate with a bunch of Objective C on a 64-bit mac as many of the core library functions you need to FFI out to pass around pairs of Int32s as a struct small enough by the x64 ABI to get shoehorned into one register, and as I was programmatically cloning Objective C APIs via template haskell I couldn't use the usual clunky C shims.
What I was doing was just using libffi with a lot of work to cache the results of ffi_prep_cif for each signature. It worked reasonably well for my purposes, but my need for it vanished and I abandoned the code in the middle of refactoring it for grander things. So if nothing else, you can at least take this as a vote of confidence that your idea isn't crazy. =) I'd also be happy to answer questions if you get stuck or need help. -Edward On Fri, Mar 14, 2014 at 7:50 AM, Yuras Shumovich <shumovi...@gmail.com>wrote: > > Hi, > > Right now ghc's FFI doesn't support c/c++ structures. > > Whenever we have foreign function that accepts or returns struct by > value, we have to create wrapper that accepts or returns pointer to > struct. It is inconvenient, but actually not a big deal. > > But there is no easy workaround when you want to export haskell function > to use it with c/c++ API that requires structures to be passed by value > (Usually it is a callback in c/c++ API. You can't change it's signature, > and if it doesn't provide some kind of "void* userdata", then you are > stuck.) > > I'm interested in fixing that. I'm going to start with 'foreign import > "wrapper" ...' stuff. > > Calling conventions for passing c/c++ structures by value are pretty > tricky and platform/compiler specific. So initially I'll use libffi for > that (it will work when USE_LIBFFI_FOR_ADJUSTORS is defined, see > rts/Adjustor.c). It will allow me to explore design space without > bothering about low level implementation details. Later it could be > implemented for native (non-libffi) adjustors. > > Is anybody interested it that? I appreciate any comments/ideas. > > Right now I don't have clear design. It would be nice to support plain > haskell data types that are 1) not recursive, 2) has one constructor and > 3) contains only c/c++ types. But it doesn't work with c/c++ unions. Any > ideas are welcome. > > An example how to use libffi with structures: > http://www.atmark-techno.com/~yashi/libffi.html#Structures > > Thanks, > Yuras > > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://www.haskell.org/mailman/listinfo/ghc-devs >
_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs
