Brussels / 3 & 4 February 2018



Foreign Function Interface and JIT using Clang/LLVM

This talk will present DragonFFI, a Clang/LLVM-based library that allows calling C functions and using C structures from any languages. It will show how Clang and LLVM are used to make this happen, and the pros/cons against similar libraries (like (c)ffi).

In 2014, Jordan Rose and John McCall from Apple presented a talk about using Clang to call C functions from foreign languages. They showed issues they had doing it, especially about dealing with various ABI.

DragonFFI provides a way to easily call C functions and manipulate C structures from any language. Its purpose is to parse C libraries headers without any modifications and transparently use them in a foreign language, like Python or Ruby. In order to deal with ABI issues previously demonstrated, it uses Clang to generate scalar-only wrappers of C functions. It also uses generated debug metadata to have introspection on structures.

Here is an example of the Python API:

$ python
>>> import pydffi
>>> lib = pydffi.FFI()
>>> lib.cdef("#include <stdio.h>", ["puts"])
>>> lib.puts("Hello world!")
Hello world!
>>> lib.compile("int foo(int a) { puts("hi!"); return a+1; }") 
>>> lib.cdef("struct A { int a; short b; }") 
>>> C = lib.A(a=4,b=5)
>>> print(C.a,C.b)
>>> lib.compile('void dump(struct A* obj) { printf("From C: %d %d\n", obj->a, obj->b"); }') 
>>> lib.dump(C)
From C: 4, 5

A high-level API provides the easy loading of a C library, that uses the previous API under the hood:

>>> lib = pydffi.LoadLibrary("/lib/",
    defines=[], include_paths=[])

>>> lib.puts("Hello FFI!")
Hello FFI!

This talk will present the tool, how Clang and LLVM are used to provide these functionalities, and the pros and cons against what other similar libraries like (c)ffi [0] [1] are doing. It also aims at gathering feedbacks and user needs that wouldn't be covered.

Code is available on github.

[0] [1]


Adrien Guinet