diff.patch

diff -Naur missing/runtimelib/runtimelib.c ./runtimelib/runtimelib.c
--- missing/runtimelib/runtimelib.c     1970-01-01 01:00:00.000000000 +0100
+++ ./runtimelib/runtimelib.c   2016-05-15 19:29:27.288102521 +0200
@@ -0,0 +1,4 @@
+int myfct()
+{
+  return 123;
+}
diff -Naur missing/lib/mylib.c ./lib/mylib.c
--- missing/lib/mylib.c 1970-01-01 01:00:00.000000000 +0100
+++ ./lib/mylib.c       2016-05-15 19:29:27.205101566 +0200
@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <dlfcn.h>
+
+void load_runtimelib()
+{
+  void *handle = dlopen("libruntimelib.so", RTLD_LAZY);
+  if (!handle) {
+    fprintf(stderr, "%s\n", dlerror());
+    exit(EXIT_FAILURE);
+  }
+
+  dlerror();
+  int (*myfct)() = (int (*)()) dlsym(handle, "myfct");
+  char *error = dlerror();
+  if (error != NULL) {
+    fprintf(stderr, "%s\n", error);
+    exit(EXIT_FAILURE);
+  }
+
+  (*myfct)();
+  dlclose(handle);
+}
diff -Naur missing/runner.c ./runner.c
--- missing/runner.c    1970-01-01 01:00:00.000000000 +0100
+++ ./runner.c  2016-05-15 19:29:27.246102037 +0200
@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <dlfcn.h>
+
+int main()
+{
+  void *handle = dlopen(XLIB, RTLD_LAZY);
+  if (!handle) {
+    fprintf(stderr, "%s\n", dlerror());
+    exit(EXIT_FAILURE);
+  }
+
+  dlerror();
+  void (*load_runtimelib)() = (void (*)()) dlsym(handle, "load_runtimelib");
+  char *error = dlerror();
+  if (error != NULL) {
+    fprintf(stderr, "%s\n", error);
+    exit(EXIT_FAILURE);
+  }
+
+  (*load_runtimelib)();
+  dlclose(handle);
+  return 0;
+}

how_to_compile.txt

Linux:
(cd runtimelib && gcc -fPIC -Wall runtimelib.c -shared -o libruntimelib.so)
(cd lib && gcc -fPIC -Wall mylib.c -shared -ldl -Wl,-rpath "$(pwd)/../runtimelib" -o libmylib.so)
gcc -fPIC -Wall -DXLIB="\"$(pwd)/lib/libmylib.so\"" runner.c -ldl -o runner

FreeBSD/OSX:
(cd runtimelib && clang -fPIC -Wall runtimelib.c -shared -o libruntimelib.so)
(cd lib && clang -fPIC -Wall mylib.c -shared -Wl,-rpath "$(pwd)/../runtimelib" -o libmylib.so)
clang -fPIC -Wall -DXLIB="\"$(pwd)/lib/libmylib.so\"" runner.c -o runner