[Caml-list] Flexlink/MinGW/Ctypes linking problem

[Matthieu Dubuget <matthieu.dubuget@gmail.com>]

Hello,

I'm currently trying to compile and link an OCaml program which calls
C++ libraries (Open Cascade). It works fine on linux, but not on
windows. I'm not sure why, and would need some advice: when I run my
program — either a bytecode version or the native one — an exception
is raised: exception Dl.DL_error("dlsym: no such symbol").

This OCaml program is calling C functions, using Ctypes.Foreign.

Those C functions are defined in a small CPP stub file with only an
extern "C" section. Those C functions are making use of the
OpenCascade C++ libraries.

Here are my (failing) attempts on windows:

I cross-compiled the C++ libraries with Debian 9 mingw-w64 toolchain,
and I checked that they are working with a small
x86_64-w64-mingw32-gcc.exe compiled C test program on windows.

I produced a DLL with something like:

    GCC = x86_64-w64-mingw32-gcc.exe
    OCCT_LIBS = TKSTEP TKMesh TKSTL  TKSTEPAttr TKSTEP209 TKSTEPBase TKXSBase TKShHealing TKTopAlgo TKGeomAlgo TKBRep TKGeomBase TKG3d TKG2d TKMath TKernel stdc++

    occ_stubs.o: occ_stubs.cpp occ_stubs.h
        $(GCC) -c -Wall -std=gnu++11 -march=x86-64 -mtune=generic -O2 -mms-bitfields -Wno-unused -Wall -I$(OCCT_INC_DIR) $< -o $@
   
    libocc_occt_stubs.dll: occ_stubs.o
        $(GCC) -shared -std=gnu99 -march=x86-64 -mtune=generic -O2 -mms-bitfields -Wno-unused -Wall -o $@ $< -L$(OCCT_BIN_DIR) $(patsubst %,-l%,$(OCCT_L_LIBS))

I checked libocc_occt_stubs.dll with a small test program compiled with:

    occt_test3.exe : occt_test3.c
        $(CC) -o $@ $< -L$(LIB_DIR) -locc_occt_stubs  -L$(OCCT_BIN_DIR) $(patsubst %,-l%,$(OCCT_LIBS))

CMXA and CMA are generated like this:

   ocOcct.cma : refHandle.cmo occt.cmo libocc_occt_stubs.dll
        ocamlfind c -a -o $@ -package $(OCAMLPACKAGES) refHandle.cmo occt.cmo -cclib -locc_occt_stubs5   -dllib libocc_occt_stubs.dll
  
    ocOcct.cmxa : refHandle.cmx occt.cmx libocc_occt_stubs.dll
        ocamlfind opt -a -o $@ -package $(OCAMLPACKAGES) refHandle.cmx occt.cmx -ccopt "-link -Wl,-rpa   th=$(STUBLIBS_DIR)" -ccopt -L$(STUBLIBS_DIR) -cclib -locc_occt_stubs

and installed with ocamlfind.

Finally, the test program is linked again the .cmxa or .cma library with:

    ocamlfind ocamlc -linkpkg -package gg -package yojson -package atdgen -package ococct -package unix -I lib -I pgm lib/aperture.cmo lib/calculette_t.cmo lib/calculette_j.cmo lib/coords.cmo lib/utils.cmo lib/product.cmo lib/essai3d.cmo lib/minim.cmo lib/probe.cmo lib/shot.cmo lib/speeds.cmo lib/conf.cmo lib/occtStub.cmo lib/calcback.cmo pgm/calculette.cmo -o pgm/calculette.byte

But when I'm running it, I get:

$ ./calculette.byte
Fatal error: exception Dl.DL_error("dlsym: no such symbol")
No master relocation table

And with the native version:

$ ./calculette.native
Fatal error: exception Dl.DL_error("dlsym: no such symbol")

What am I doing wrong?

Thanks

-- 
Matthieu Dubuget