=================
Building uClibc++
=================

.. warning:: 
    Migrated from: 
    https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=139629550 
    and is probably outdated

A version of `uClibc++ <http://cxx.uclibc.org/>`_ has been ported to NuttX and is available in the NuttX
uClibc++ GIT repository at `Bitbucket.org <https://bitbucket.org/nuttx/uclibc/>`_ . This version of uClibc++ was
adapted for NuttX by the RGMP team.

This custom version of uClibc++ resides in the NuttX repository at:

  https://bitbucket.org/nuttx/uclibc/

rather than in the main NuttX source tree, due to licensing issues: NuttX is
licensed under the permissive, modified BSD License; uClibc++, on the other
hand, is licensed under the stricter GNU LGPL Version 3 license.

General build instructions are available in the uClibc++ `README.txt <https://bitbucket.org/nuttx/uclibc/src/master/README.txt>`_ 
file. Those instructions are not repeated here. This page documents specific 
issues encountered when building this NuttX version of uClibc++ and how they 
are resolved.

Undefined Reference to ``_impure_ptr``
======================================

**Problem**

When building uClibc++, you may encounter an undefined reference to
``_impure_ptr`` similar to:

.. code-block:: none

   LD: nuttx
   .../arm-none-eabi/lib/armv7e-m\libsupc++.a(vterminate.o): In function
   `__gnu_cxx::__verbose_terminate_handler()`:
   vterminate.cc:(.text._ZN9__gnu_cxx27__verbose_terminate_handlerEv+0xfc):
   undefined reference to `_impure_ptr'

**Solution**

A definitive, elegant solution is not known, but the following workaround has
proven to work:

1. Locate the directory where you can find ``libsupc++``:

   .. code-block:: console

      arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -print-file-name=libsupc++.a

2. Go to that directory and save a copy of ``vterminate.o`` (in case you need
   it later):

   .. code-block:: console

      cd <the-directory-containing-libsupc++.a>
      arm-none-eabi-ar.exe -x libsupc++.a vterminate.o

3. Remove ``vterminate.o`` from the library. At build time, the uClibc++
   package will provide a usable replacement:

   .. code-block:: console

      arm-none-eabi-ar.exe -d libsupc++.a vterminate.o

4. At this point, NuttX should link with no problem. If you ever want to
   restore the original ``vterminate.o`` to ``libsupc++.a``, you can do so
   by running:

   .. code-block:: console

      arm-none-eabi-ar.exe rcs libsupc++.a vterminate.o

After removing ``vterminate.o`` from the standard library, the
uClibc++-provided ``vterminate.o`` becomes the active implementation and
prevents references to ``_impure_ptr`` from arising during linkage.

.. note::
   Always exercise caution when modifying toolchain libraries. This
   workaround is known to be effective but it replaces standard library
   objects, which may have side effects in other toolchain usage scenarios.