To generate bindings, some pypy macros are required (included in /include). I've used bindgen wrapper.h -o ./src/cpyext_ffi -- -I./Include

The main pain point is we need to manually rename the functions from their pypy expanded form PyPy.. to Py to keep convention (note that the link command are still valid for libpypy3-c)

I've used this simple script (yes - it should probably be included in the build.rs)

with open('/Users/omerba/Workspace/pypy_ffi/src/ffi_bindgen.rs', 'r') as f:
    src = f.read()

r = re.sub(r"(?!\".*)PyPy(?!.*\")", "Py", src)

with open('/Users/omerba/Workspace/pypy_ffi/src/ffi_bindgen.rs', 'w') as f:
    f.write(r)

(also had to renamed like 3 functions manually back to PyPy since they were included twice)