Re: [Caml-list] Building a mixed C / OCaml static library to be used from C

[John Whitington <john@coherentgraphics.co.uk>]

Hi,

Gerd Stolpmann wrote:
> Am Donnerstag, den 22.08.2013, 18:34 +0100 schrieb John Whitington:
>> Hi,
>>
>> I have the following recipe to build a static library of C functions
>> from a mixed ocaml / c codebase. The idea is that the final linking step
>> to build target 'test' won't require any special flags:
>>
>>
>> CAMLBASE = /Users/john/.opam/4.00.1/lib/
>>
>> mklib: cpdflib.mli cpdflib.ml cpdflibwrapper.c
>> 	ocamlfind ocamlc -package cpdf cpdflib.mli;
>> 	ocamlfind ocamlopt -package cpdf -c cpdflib.ml;
>> 	ocamlfind ocamlc cpdflibwrapper.c;
>> 	ocamlfind ocamlopt -I $(CAMLBASE)cpdf -I $(CAMLBASE)camlpdf \
>>             -output-obj -o cpdflib.o \
>>             unix.cmxa bigarray.cmxa camlpdf.cmxa cpdf.cmxa cpdflib.cmx;
>> 	ar -x $(CAMLBASE)camlpdf/libcamlpdf_stubs.a;
>> 	ar -x $(CAMLBASE)ocaml/libasmrun.a;
>> 	ar cr cpdflib.a *.o
>>
>> test:   cpdflib.a cpdflibtest.c
>> 	cc cpdflibtest.c cpdflib.a -o test\
>>             -L $(CAMLBASE)ocaml -lbigarray -lunix
>>
>> clean:
>> 	rm __.SYMDEF\ SORTED *.o *.cmx *.cmi *.a test
>>
>>
>> (Here, cpdflib.ml, cpdflib.mli and cpdflibwrapper.c form the C interface
>> to the OCaml functions. cpdflibtest.c calls caml_startup and then any
>> caml functions it likes).
>>
>> This works. However, I'm having trouble getting rid of "-L
>> $(CAMLBASE)ocaml -lbigarray -lunix" -- i'd like the person linking with
>> my cpdflib.a not to need any dependencies at all.
>>
>> When I add two more lines
>>
>>           ar -x $(CAMLBASE)ocaml/bigarray.a;
>>           ar -x $(CAMLBASE)ocaml/unix.a;
>
> These are the wrong two libs. bigarray.a and unix.a are already
> contained in cpdflib.a. What you need are libbigarray.a and libunix.a.

Ah. A schoolboy error. Thanks!

However, it looks like this might not be possible anyway. In this thread...

http://caml.inria.fr/pub/ml-archives/caml-list/2007/11/c0ce27aa2dd792643615b6b705750657.en.html

...Alain Frisch comments on the method above, saying:

> Ok, that's a hack to merge one library, plus more object files into a
> library. I know it is mentioned in the OCaml manual. Personally, I would
> not recommend to do that (you'll be stuck if you need to include e.g.
> libunix.a).

So, unless I can find a way to get partial linking with ld -r to work, 
the best I have for now is:

CAMLBASE = /Users/john/.opam/4.00.1/lib/

mklib: cpdflib.mli cpdflib.ml cpdflibwrapper.c
	ocamlfind ocamlc -package cpdf cpdflib.mli;
	ocamlfind ocamlopt -package cpdf -c cpdflib.ml;
	ocamlfind ocamlc cpdflibwrapper.c;
	ocamlfind ocamlopt -I $(CAMLBASE)cpdf -I $(CAMLBASE)camlpdf \
           -output-obj -o cpdflib.o \
           unix.cmxa bigarray.cmxa camlpdf.cmxa cpdf.cmxa cpdflib.cmx;
	cp $(CAMLBASE)ocaml/libasmrun.a libcpdf.a;
	ar -x $(CAMLBASE)camlpdf/libcamlpdf_stubs.a;
	ar r libcpdf.a *.o

test:   libcpdf.a cpdflibtest.c
	cc cpdflibtest.c -o test -L. -lcpdf -lbigarray -lunix

clean:
	rm __.SYMDEF\ SORTED *.o *.cmx *.cmi *.a test

The end-user of the library still needs three -l options, but I need 
only ship the three .a files (libcpdf, libbigarray, libunix), which I 
suppose is not much harder on the end user than shipping one.

Obviously, I hope most people will be building from source, but I do 
need to ship binary libraries too.

Thanks,

-- 
John Whitington
Director, Coherent Graphics Ltd
http://www.coherentpdf.com/