Re: about header file parsing

[Basile Starynkevitch <basile@starynkevitch.net>]

On 1/9/19 4:52 PM, Marc Nieper-Wißkirchen wrote:
> How would you handle, for example, gmp's header file?
> https://gmplib.org/repo/gmp/file/default/gmp-h.in
>
> Almost all of the public API is behind #define's. So even if the
> gcc_jit_context is filled with the functions that are declared in the
> header, one still needs to know the ABI of GMP to know which functions
> to call.
>
> In order to make it work in the general case (if this is at all
> possible), I think one has to turn the C frontend of GCC into a
> library (like libgccjit has turned the GCC middle/backend into a
> library). This hypothetical library X has its own context K that is
> populated by expanding and parsing the relevant header files.
>
> In this context K, we can then ask for expansion of strings of C
> tokens (e.g. in expression or statement context). Library X then
> returns the expansion in term of, say, a C-specific GENERIC tree,
> which can then be converted into/wrapped into a gcc_jit_object.
>
> -- Marc



AndI (Basile) wrote:

>>> in practice C macros are very important (and a lot of API for C are
>>> using macros, see also macros such as WIFEXITED in wait(2) on some
>>> Linux
>>> system).
>>>
>>> We have to admit that C and libgccjit are different "languages" (even
>>> if
>>> conceptually very close). And a C API is not exactly a set of
>>> "objects"
>>> that libgccjit can handle.
>> They're not the same, but it is important that libgccjit be able to
>> interoperate well with C APIs.


I'm not sure that general goal is reasonable. libgccjit is already able 
to interoperate with a library written in C. Unfortunately, a C API is 
not just a library, but also macros (such as EOF or WIFEXITED), and we 
cannot expect libgccjit to deal with these.


On Linux libgccjit is already capable to call any function in some ELF 
library which uses the C calling conventions, and that is already excellent.

And that limitation is not particular to libgccjit: any implementor of 
some interpreter or compiler has to deal specially with C macros, and 
handle them in an ad-hoc way.

We have to admit that in general C APIs are complex beasts, even if most 
of the time they are "simple" enough.

Regards

-- 
Basile STARYNKEVITCH   == http://starynkevitch.net/Basile
opinions are mine only - les opinions sont seulement miennes
Bourg La Reine, France