I am forking the old luaffifb project to get it working with my lua-ffi-wasm project, to run my luajit opengl sdl framework in browser.

Fixes I've made

• CType objects as well as CData objects can now use their metatables' __index - just like in vanilla LuaJIT.
• Arithmetic on pointers no longer calls into the metatmethod of the underlying CType - just like in vanilla LuaJIT.
• luaffifb's tonumber now handles float, double, complex float, complex double, as well as integer types; and it no longer converts pointers and arrays - just like in vanilla LuaJIT.
• bool is no longer serialized as unsigned bool - just like in vanilla LuaJIT.
• For CALL_WITH_LIBFFI I no longer replace C functions with lua_CFunction's that might run a bit faster but cannot be compared or converted to CData. The trade off is now there's a separate Lua __call per C-function call, but now we do get casting C functions to pointers and operate on them.
• CType objects now have __eq
• All the ffi library arguments that could be either type or ctype objects now supports the "$" arguments.
• __attribute__((aligned())) now handles expressions.
• __attribute__((aligned())) now works on all variables of the statement, before it would just apply to the first.
• struct now has attributes, not just fields in struct.
• arrays-of-ctypes no longer metatable-index into their base-ctype (which was incorrect buggy behavior).
• cdata-of-arrays-of-ctypes " " " " ".
• defining ffi metatypes of arrays-of-ctypes now errors like it should.
• ffi.string and ffi.copy with a definite size will now handle any kind of pointer, not just char* pointers.
• ffi.string now works on lua strings.

Changes I've made

• ffi.null as well as ffi.NULL
• Added CALL_WITH_LIBFFI for non-JIT LibFFI-based calling, especially so this can get working in WASM. At first I dismissed https://github.com/q66/cffi-lua and https://github.com/zhaojh329/lua-ffi for lacking key features that luaffifb had like bitflags, but now I see the good side of using libffi over hacked in dynasm jit calls, and that is for wasm support. so I haven't yet finished it but maybe I will look at these for inspiration.

Changes I plan to make:

• Indexing fields that aren't there should throw exceptions. I hate it, but I'm staying true to LuaJIT. or maybe I shouldn't, idk...
• CTypes can only be up to 3 pointers deep. libjpeg breaks this. Do like luajit and let the CType hold a pointer to the base-CType. It's starting to look more and more like the pure-lua ffi implementation I made should just be converted over and it'll be more feature-rich than the CType/CData implementation here ... though this implementation seems to have the most superior parser.
• Looks like comparing function-pointers was always breaking the test suite ... better fix that.
• get cdecl/fastcall/stdcall/thiscall working in the libffi-based calling.

Here's the original readme:

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About

This is a library for calling C function and manipulating C types from lua. It is designed to be interface compatible with the FFI library in LuaJIT (see http://luajit.org/ext_ffi.html). It can parse C function declarations and struct definitions that have been directly copied out of C header files and into lua source as a string.

This is a fork of https://github.com/jmckaskill/luaffi

Source

https://github.com/facebook/luaffifb

Platforms

Currently supported:

• Linux x86/x64
• OS X x86/x64

Runs with Lua 5.1, 5.2, and 5.3

Build

In a terminal:

git clone https://github.com/facebook/luaffifb
cd luaffifb
luarocks make

Documentation

This library is designed to be source compatible with LuaJIT's FFI extension. The documentation at http://luajit.org/ext_ffi.html describes the API and semantics.

Pointer Comparison

Use ffi.NULL or ffi.null instead of nil when checking for NULL pointers.

  ffi.new('void *', 0) == ffi.NULL -- true

Known Issues

• Comparing a ctype pointer to nil doesn't work the same as in LuaJIT (see above). This is unfixable with the current metamethod semantics.
• Constant expressions can't handle non integer intermediate values (eg offsetof won't work because it manipulates pointers)
• Not all metamethods work with Lua 5.1 (eg char* + number). This is due to the way metamethods are looked up with mixed types in Lua 5.1. If you need this upgrade to Lua 5.2 or use boxed numbers (uint64_t and uintptr_t).
• All bitfields are treated as unsigned (does anyone even use signed bitfields?). Note that "int s:8" is unsigned on unix x86/x64, but signed on windows.

How it works

Types are represented by a CType structure and an associated user value table. The table is shared between all related types for structs, unions, and functions. It's members have the types of struct members, function argument types, etc. The CType structure then contains the modifications from the base type (eg number of pointers, array size, etc).

Types are pushed into lua as a userdata containing the CType with a user value (or fenv in 5.1) set to the shared type table.

Boxed cdata types are pushed into lua as a userdata containing the struct cdata structure (which contains the CType of the data as its header) followed by the boxed data.

The functions in ffi.C provide the cdata and ctype metatables and ffi.* functions which manipulate these two types.

C functions (and function pointers) are pushed into lua as a lua c function with the function pointer cdata as the first upvalue. The actual code is JITed using dynasm (see call_x86.dasc). The JITed code does the following in order:

1. Calls the needed unpack functions in ffi.C placing each argument on the HW stack
2. Updates errno
3. Performs the C call
4. Retrieves errno
5. Pushes the result back into lua from the HW register or stack