Question

I’m having an issue with the order in which the libraries are added to the linker. Previously built libraries by ocamlbuild are linked in after the list of libraries I included by the flag rule. And, I don’t see any way to define this type of dependency in myocamlbuild.ml either.

Specifically, the issue comes in linking with a previously built library (gzcaml) that requires a library itself (z). Because of the added strictness in newer versions of gcc the argument -lz must appear after libgzcaml.a.

I am including all these libraries with,

flag ["ocaml"; "link"]
    (S (process "-cclib" clibs))

where process creates a list alternating the library and A"-cclib", appropriately.

Also, additional libraries are appended (from the verbose output, -lm and -ldl) but I have no idea how I can modify/append these? (this would instantly solve my problem).

My myocamlbuild.ml is quite long else I would have included it here. I have tried moving the above code around to the bottom of the After_rules, to the top. And it does change the order, but never after the built libraries (c and otherwise) that ocamlbuild created previously.

---

EDIT
Below are code snippets I’ve used in my configure script and ocamlbuild to solve the issue above. Cheers!

in configure.ac

oCFLAGS="$CFLAGS"
CFLAGS="$FLAGS -Wl,--no-as-needed"
AC_MSG_CHECKING([whether we need to add --no-as-needed linking option])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], 
                                     [[ 
                                        int main(){ return 0; } 
                                    ]])], 
                  [AC_MSG_RESULT([yes]); CC_NOASNEEDED="true"],
                  [AC_MSG_RESULT([no]); CC_NOASNEEDED="false"]) 
CFLAGS=$oCFLAGS

in myocamlbuild.ml.in

 if @CC_NOASNEEDED@ then
     flag ["ocaml"; "link"]
         (S [A"-cclib";A"-Wl,--no-as-needed"]);

Answer 1

This is not an answer, but a workaround – disable this new linker behaviour with -cclib -Wl,--no-as-needed.

I guess this should be reported as a bug to mantis. Specifically, ocamlbuild should guarantee that options from flags are inserted into command-line in the same order as they are encountered in the source (this is the case now afair), and ocamlopt should preserve the order of -cclib and -ccopt arguments wrt other entries on the command-line (this is NOT the case now).