RFC on plans to implement a c2ffi->cffi generator

[Luís Oliveira]

On Wed, Dec 9, 2015 at 9:10 PM, Attila Lendvai <attila at lendvai.name> wrote:
> c2ffi is a tool written in C that uses the llvm/clang libs to generate
> a json file from C headers. it's like gcc-xml, only much better. the
> json file has explicit offsets and sizes, etc... see an example here:
>
> https://github.com/rpav/ZMQ4L/blob/master/src/autospec/zmq.x86_64-pc-linux-gnu.spec
>
> once this json has been generated for your platform, it can be checked
> into the repo and no external tool is needed afterwards.

That is very nice. The need for a C compiler during compilation of
things that use cffi-grovel, particularly on Windows where,
ironically, binary compatibility is easier.


> cl-autowrap uses such json files to generate an alternative FFI API,
> but i'd like to use vanilla CFFI, so i'm planning to write some code
> towards this direction, but i'd like to hear some input on this before
> i start working on anything...

Cool!


> i imagine it to be similar to how groveling works in iolib, namely:
> generate the intermediate files from the json files using some ASDF
> integration, and then compile the lisp files as any other lisp files.

I was thinking it'd be pretty neat to COMPILE-FILE the spec file
directly using a custom readtable, but whatever's easier. :-)


> my first question is why isn't this ASDF integration, or something
> like this, ported into cffi for the gorveler? is there any other
> reason besides nobody has done it yet?
>
> https://github.com/sionescu/iolib/blob/master/src/grovel/asdf.lisp

Not sure what you mean. This ASDF integration is in cffi-grovel.


BTW, the scope of the groveller is quite narrow. Things like c2ffi are
for grabbing everything a header file has got to offer. The groveller
way is just "hey, I know this constant exists, grab me its value
please". But, if something like c2ffi turns out to work very well,
then we can reimplement the groveller's API on top of it, sure.

Have you seen <https://github.com/rpav/c2ffi-cffi>?


> does anyone see some showstoppers? e.g. can i lay out defcstruct
> fields with explicit offsets? NOTICE-FOREIGN-STRUCT-DEFINITION
> suggests so.

I don't see any showstoppers. cl-autowrap is built on top of CFFI, as
is the groveller.


> should this code go into a cffi-c2ffi.asd or into a standalone
> project? any ideas for a name?

cffi-c2ffi sounds good and I'd be happy to merge into CFFI.

Looking forward to your next steps!

Cheers,

-- 
Luís Oliveira
http://kerno.org/~luis/