docs: Add macos build documentation

Type: docs

Change-Id: Iee03aacab2cfcb4e87190302dc641e8273b7f096
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>

docs/gettingstarted/developers/cross_compile_macos.rst

@@ -0,0 +1,57 @@
+.. _cross_compile_macos :
+
+Cross compilation on MacOS
+==========================
+
+This is a first attempt to support Cross compilation of VPP on MacOS for development (linting, completion, compile_commands.json)
+
+
+**Prerequisites**
+
+* You'll need to install the following packages
+
+.. code-block:: bash
+
+  pip3 install ply
+  brew install diffutils gnu-sed pkg-config ninja crosstool-ng
+
+* You'll also need to install ``gnu-ident 2.2.11`` to be able to ``make checkstyle``. You can get it from `GNU <https://www.gnu.org/prep/ftp.html>`_
+* You should link the binaries to make them available in your path with their original names e.g. :
+
+.. code-block:: bash
+
+  ln -s $(which gsed) /usr/local/bin/sed
+  ln -s $(which gindent) /usr/local/bin/indent
+  ln -s /usr/local/Cellar/diffutils/3.7/bin/diff /usr/local/bin/diff
+
+
+**Setup**
+
+* Create a `cross compile toolchain <https://crosstool-ng.github.io/>`_
+* Create a case sensitive volume and mount the toolchain in it e.g. in ``/Volumes/xchain``
+* Create a xchain.toolchain file with ``$VPP_DIR/extras/scripts/cross_compile_macos.sh conf /Volumes/xchan``
+
+For now we don't support e-build so dpdk, rdma, quicly won't be compiled as part of ``make build``
+
+To build with the toolchain do:
+
+.. code-block:: bash
+
+  $VPP_DIR/extras/scripts/cross_compile_macos.sh build
+
+
+To get the compile_commands.json do
+
+.. code-block:: bash
+
+  $VPP_DIR/extras/scripts/cross_compile_macos.sh cc
+  # >> ./build-root/build-vpp[_debug]-native/vpp/compile_commands.json
+
+
+
+This should build vpp on MacOS
+
+
+Good luck :)
+
+

docs/gettingstarted/developers/index.rst

@@ -40,3 +40,4 @@ The Developers section covers the following areas:
    buildwireshark
    punt
    quic_plugin
+   cross_compile_macos.rst