December 2015 - cffi-devel - mailman3.common-lisp.net

Calling a struct-by-value by reference
by Liam Healy 23 Dec '15

23 Dec '15

Hi Attila, Re: https://bugs.launchpad.net/cffi/+bug/1528719 (There is an error in the sample code, the struct is called 'struct-pair, not 'pair.) Here is a simpler exhibition of the problem (sumpair (convert-to-foreign '(40 . 2) '(:struct struct-pair))) The value #.(SB-SYS:INT-SAP #X7FFFEC003560) is not of type LIST. [Condition of type TYPE-ERROR] So, you've said the function is call-by-value, and then you want to pass a pointer to the structure, and it makes sense there's an error. You have to assume a translator, because that's the only way to have a structure by value. I understand the desire to be able to pass a pointer instead, but my approach would be different. I'd change the function argument definition and extend the syntax to say that you're going to pass a pointer, e. g. (defcfun "sumpair" :int (p (:struct struct-pair) :pointer)) which I would have expand to something like (DEFUN SUMPAIR (P) (WITH-FOREIGN-OBJECTS ((CFFI::ARGVALUES :POINTER 1) (CFFI::RESULT ':INT)) (MEM-REF (PROGN (LOOP :FOR CFFI::ARG :IN (LIST P) :FOR COUNT :FROM 0 :DO (SETF (MEM-AREF CFFI::ARGVALUES :POINTER COUNT) CFFI::ARG)) (CFFI::CALL (CFFI::PREPARE-FUNCTION "sumpair" ':INT '((:STRUCT STRUCT-PAIR)) ':DEFAULT-ABI) (FOREIGN-SYMBOL-POINTER "sumpair") CFFI::RESULT CFFI::ARGVALUES) CFFI::RESULT) :INT))) So now you can do (sumpair (convert-to-foreign '(40 . 2) '(:struct struct-pair))) 42 I don't like the idea of hacking up translate-into-foreign-memory because you're doing extra work that way, and as you can see, the expansion can be simpler than the translated case. The only disadvantage of this approach is that you'll have to have two different functions if you will be calling the same function with a CL object and with a foreign pointer. I imagine that this won't happen very often; I'm guessing this is for chaining together foreign calls in CL, where the foreign structure never sees the light of day (=lisp form). (The defcfun won't expand the way I've shown yet, but the pseudo-expansion actually can be compiled and run.) What do you think? Liam

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Type propagation proposal
by Attila Lendvai 23 Dec '15

23 Dec '15

i wrote up some ideas here: https://github.com/cffi/cffi/wiki/Type-propagation-proposal you're invited to comment/edit it. -- • attila lendvai • PGP: 963F 5D5F 45C7 DFCD 0A39 -- “The first thing you have to do if you want to raise nice kids, is you have to talk to them like they are people instead of talking to them like they're property.” — Frank Zappa (1940–1993), 'The Howard Stern Show' (1987)

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RFC on plans to implement a c2ffi->cffi generator
by Attila Lendvai 20 Dec '15

20 Dec '15

dear list, 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-… once this json has been generated for your platform, it can be checked into the repo and no external tool is needed afterwards. 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... 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. 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 does anyone see some showstoppers? e.g. can i lay out defcstruct fields with explicit offsets? NOTICE-FOREIGN-STRUCT-DEFINITION suggests so. should this code go into a cffi-c2ffi.asd or into a standalone project? any ideas for a name? -- • attila lendvai • PGP: 963F 5D5F 45C7 DFCD 0A39 -- Blaming the prince of the fools should not blind anyone to the vast confederacy of fools that made him their prince.

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Using pkg-config (hdf5)
by Liam Healy 08 Dec '15

08 Dec '15

Debian has relocated hdf5 includes and libraries in serial/, which means that hdf5-cffi does not compile. See this issue: https://github.com/HDFGroup/hdf5-cffi/issues/61. I am trying to come up with a CFFI solution. It seems like pkg-config-cflags should do the job for me, as pkg-config is installed and does the right thing: pkg-config --libs hdf5 -L/usr/lib/x86_64-linux-gnu/hdf5/serial -lhdf5 pkg-config --cflags hdf5 -I/usr/include/hdf5/serial However, I put a line (pkg-config-cflags "hdf5" :optional t) in hfd5-cffi/hdf5/grovel.lisp and got nothing useful; it is clear it is running pkg-config but the result never makes it into the cc arg list. (ql:quickload :hdf5-cffi) To load "hdf5-cffi": Load 1 ASDF system: hdf5-cffi ; Loading "hdf5-cffi" [package hdf5]; pkg-config hdf5 --cflags -I/usr/include/hdf5/serial ; cc -m64 -o /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/grovel__grovel-tmpGHU3ALSV -I/home/healy/languages/lisp/cffi/ /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/grovel__grovel.c ; /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/grovel__grovel /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/grovel__grovel.grovel-tmp.lisp ; cc -m64 -o /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/h5-grovel__grovel-tmpAAURSO1 -I/home/healy/languages/lisp/cffi/ /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/h5-grovel__grovel.c /home/healy/.cache/common-lisp/sbcl-1.2.15-linux-x64/home/healy/languages/lisp/hdf5-cffi/hdf5/h5-grovel__grovel.c:6:18: fatal error: hdf5.h: No such file or directory #include <hdf5.h> ^ compilation terminated. Is this a problem of CFFI or dies the pkg-config-cflags form need to be somewhere else? Liam

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