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ktakashi / r6rs-pffi

Portable Foreign Function Interface (FFI) for R6RS
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Support specifying ABI properties for `foreign-procedure` #27

Closed lemvik closed 2 years ago

lemvik commented 2 years ago

Currently there is no (?) way to specify additional ABI properties (calling convention, etc.) of foreign procedures in Chez (and other) implementation of pffi.

Chez supports those (here is the doc) and most of the time they are not really required to be able to build an FFI wrapper around C library. However, there is an exception to that, in particular, on MacOS X M1.

This comment in a Racket Chez branch mentions that in order to correctly set up a call for C procedure that uses va_list on an Apple Silicon architecture one needs to provide (__varargs_after X) ABI specifier.

Inability to specify it prevents akku Scheme package manager from working on M1 Mac OS - it binds to libcurl and uses curl_easy_setopt function that is actually a vararg-taking C func.

On the other hand, I'm not sure if any other Scheme implementation actually allows specifying ABI conventions so I wonder what would be the best way to add such support in a uniform way.

ktakashi commented 2 years ago

Firstly, I think varargs is actually not supported by this library (I don't see the argument type marker for this, and I vaguely remember that indeed not all implementations support it). It may work in some implementations but not all of them.

For the ABI properties, it might be better to automatically handle in Chez's foreign-procedure as other implementations do those things (e.g. Larceny is calling ffi-get-abi to get proper ABI inside of the make-c-function).

ktakashi commented 2 years ago

I've created issue #25 to (officially) support varargs. Thanks for reminding me :D

lemvik commented 2 years ago

Thank you!

ktakashi commented 2 years ago

I've added implementation specific calling convention capability to foreign-procedure, though bare Chez doesn't support (__varargs_after X). It seems that's Racket specific thing. So, maybe you also need to ask Chez developers to support variadic arguments (or something similar with __varargs_after).

lemvik commented 2 years ago

Thank you for the change!