Notes on struct passing

Notes about ffi in other languages

PyPy's new cffi module uses libffi (also ffi of Pure and Haskell).
the main performance cost with libffi is generating the caller asm thunk, but this can be cached: https://github.com/tearsofphoenix/VeritasKit/issues/1
I didn't find any real benchmarks of libffi, but this seems to indicate the overhead is ~2-3x (ctypes and cffi both use libffi underneath) http://tungwaiyip.info/blog/2009/07/16/ctype_performance_benchmark
the types of situations where struct byval is necessary can probably afford the performance hit (?)
one other thing: LuaJIT FFI does not rely on libffi at all, and seems to do most of calling logic in about 2k lines: http://repo.or.cz/w/luajit-2.0.git/blob/master:/src/lj_ccall.c http://repo.or.cz/w/luajit-2.0.git/blob/master:/src/lj_cconv.c (it has good enough struct support to wrap both libLLVM and libclang: https://github.com/Neopallium/lua-clang-cindex https://github.com/grrrwaaa/luaclang ).
here is a simple example using libffi with LLVM: http://llvm.org/docs/doxygen/html/ExternalFunctions_8cpp_source.html

Docs:

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