This line:

QMAKE_CFLAGS += -rdynamic -lm -L/-dl

should be

QMAKE_LFLAGS += -rdynamic -lm -L/-dl

I call the function via pointer to function, like this:

typedef void (*native_fn)(eVm*);

native_fn load_so(const char* libname, const char* symname)
{
    void* so_library = dlopen(libname, RTLD_LAZY);
    if (so_library == NULL)
    {
        fprintf(stderr, "Error loading %s\n:%s", libname, dlerror());
    }
    else
    {
        void* initializer = dlsym(so_library, symname);
        if (initializer == NULL)
        {
            fprintf(stderr, "Error loading %s.%s:\n%s", libname, symname, dlerror());
        }
        else
        {
            fprintf(stdout, "Loading %s:%s\n", libname, symname);
            native_fn sobj = (native_fn)initializer;
            return sobj;
        }
    }
    return NULL;
}

The function is then stored inside an object's metatable like this:

    ...
    eObject name = eobj_string("addtest");
    eFunction* f = efunction_new(OBJ_AS_CSTR(name), NULL);
    f->fp = load_so("./modtest/libtest_add.so", "wr_add_test");
    f->is_native = true;
    eObject func = ((eObject){ EFUNCTION, .value.object=f });
    edict_insert(&vm->globals,  OBJ_AS_CSTR(name), func);
    ...

addtest is the named used to search the function and call it.
Thanks a lot for your help.

That sounds a bit strange. How do you make your library call that function from your main application ?