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From: Benedikt Meurer <benedikt.meurer@googlemail.com>
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Date: Wed, 14 Sep 2011 17:59:24 +0200
Cc: OCaml List <caml-list@yquem.inria.fr>
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To: Romain Bardou <bardou@lri.fr>
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Subject: Re: [Caml-list] Link a .so/.dll dynamically


On Sep 14, 2011, at 17:56 , Romain Bardou wrote:

> Le 14/09/2011 17:09, Benedikt Meurer a écrit :
>> 
>>> My first problem is: I tried something similar for native code (using ocamlopt instead of ocamlc, .cmx instead of .cmo and .cmxa instead of .cma) but ocamlmklib fails with the following error:
>>> 	/usr/bin/ld: wrapper.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC
>>> 	wrapper.o: could not read symbols: Bad value
>>> 	collect2: ld returned 1 exit status
>>> I have absolutely no idea what this means, I'm really confused here and Google does not help.
>> 
>> The error messages already includes the answer, you need to pass -fPIC to the C compiler when compiling wrapper.c, i.e.
>> 
>> $ gcc -c -fPIC -o wrapper.o wrapper.c
> 
> Thanks for your quick answer.
> 
> Actually I tried adding the -fPIC option like this:
> 
> 	ocamlopt -c -ccopt -fPIC wrapper.c
> 	ocamlopt -c mylib.ml
> 	ocamlmklib wrapper.o mylib.cmx -o mylib
> 	ocamlopt -c main.ml
> 	ocamlopt dynlink.cmxa main.cmx -o main
> 	CAML_LD_LIBRARY_PATH=. ./main mylib.cmxa
> 
> But when Dynlink.load is called, it fails with the following error:
> 
> 	error loading shared library: /home/.../mylib.cmxa: invalid ELF header
> 
> I'm thinking this is because the .cmxa has not been compiled with the -shared option, but I don't know how to tell ocamlmklib to compile with the -shared option.

$ ocamlmklib -ldopt -shared wrapper.o mylib.cmx -o mylib

> Romain Bardou

Benedikt