unikernel/duniverse/dune_/doc/reference/extra-objects.rst

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+Extra Objects
+-------------
+
+It's possible to specify native object files to be packaged with OCaml
+libraries or linked into OCaml executables. Do this by using the
+``extra_objects`` field of the ``library`` or ``executable`` stanzas.
+For example:
+
+.. code:: dune
+
+    (executable
+     (public_name main)
+     (extra_objects foo bar))
+
+    (rule
+     (targets foo.o bar.o)
+     (deps foo.c bar.c)
+     (action (run ocamlopt %{deps})))
+
+This example builds an executable which is linked against a pair of native
+object files, ``foo.o`` and ``bar.o``. The ``extra_objects`` field takes a list
+of object names, which correspond to the object file names with their path and
+extension omitted (in contrast, ``(rule)`` manipulates file names, so the
+extension needs to be provided).
+
+In this example, the sources corresponding to the objects (``foo.c`` and
+``bar.c``)  are assumed to be present in the same directory as the OCaml source
+code, and a custom ``rule`` is used to compile the C source code into object
+files using ``ocamlopt``. This is not necessary; one can instead compile foreign
+object files manually and place them next to the OCaml source code.