.. _BUILD:gcc:

GCC backend
###########

.. TODO :: Instructions to build GHDL with GCC backend on Windows are not available yet.

.. rubric:: Requirements

* GCC (Gnu Compiler Collection)
* GNAT (Ada compiler for GCC)
* GCC source files. Download and untar the sources of version 4.9.x, 5.x, 6.x or 7.x.

.. HINT :: There are some dependencies for building GCC (``gmp``, ``mpfr`` and ``mpc``). If you have not installed them on your system, you can either build them manually or use the ``download_prerequisites`` script provided in the GCC source tree (recommended): ``cd /path/to/gcc/source/dir && ./contrib/download_prerequisites``.

* First configure GHDL, specify GCC source directory and installation prefix (like  ``/usr/local`` or ``/opt/ghdl``).
* Next, invoke ``make copy-sources`` to copy GHDL sources in the source directory.
* Then, configure GCC. The list of ``--disable`` configure options can be adjusted to your needs. GHDL does not require all these optional libraries and disabling them will speed up the build.
* Now, build and install GCC with ``make``.
* Last, build and install GHDL libraries.

.. rubric:: Example:

.. code-block:: Bash

 $ cd <ghdl>
 $ mkdir build
 $ cd build
 $ ../configure --with-gcc=/path/to/gcc/source/dir --prefix=/usr/local
 $ make copy-sources
 $ mkdir gcc-objs; cd gcc-objs
 $ /path/to/gcc/source/dir/configure --prefix=/usr/local --enable-languages=c,vhdl \
 --disable-bootstrap --disable-lto --disable-multilib --disable-libssp \
 --disable-libgomp --disable-libquadmath
 $ make -j2 && make install
 $ cd /path/to/ghdl/source/dir/build
 $ make ghdllib
 $ make install

.. HINT :: Note that the prefix directory to configure ``gcc`` must be the same as the one used to configure GHDL. If you have manually built ``gmp``/``mpfr``/``mpc`` (without using the script in ``contrib``), and, if you have installed them in a non-standard directory, you may need to add ``--with-gmp=GMP_INSTALL_DIR``.

.. HINT :: If your system gcc was configured with ``--enable-default-pie`` (check if that option appears in the output of ``gcc -v``), you should also add it.

.. HINT :: If you don't want to install ``makeinfo``, do ``make install MAKEINFO=true`` instead.

.. HINT :: Once GCC (with GHDL) has been built once, it is possible to work on the GHDL source tree without copying it in the GCC tree. Commands are::

  $ make ghdl1-gcc           # Build the compiler
  $ make ghdl_gcc            # Build the driver
  $ make libs.vhdl.local_gcc # Compile the vhdl libraries
  $ make grt-all             # Build the GHDL runtime
  $ make install.vpi.local   # Locally install vpi files

  In ``src/ortho/gcc``, create a ``Makefile.conf`` file that sets the following
  variables:

  .. CODE:: Bash

    AGCC_GCCSRC_DIR=/path/to/gcc/sources
    AGCC_GCCOBJ_DIR=/path/to/gcc/build

  If your system gcc was built with ``--enable-default-pie``, add
  ``-no-pie`` option for linking.

.. HINT :: For ppc64 (and AIX ?) platform, the object file format contains an identifier for the source language. Because gcc doesn't know about VHDL, gcc crashes very early. This could be fixed with a very simple change in ``gcc/config/rs6000/rs6000.c``, ``function rs6000_output_function_epilogue`` (as of gcc 4.8):

	  .. CODE:: diff

 	 	 	  || ! strcmp (language_string, "GNU GIMPLE")
 	 	 	  || ! strcmp (language_string, "GNU Go")
 	 	 	  || ! strcmp (language_string, "GNU D")
 	 	-	  || ! strcmp (language_string, "libgccjit"))
 	 	+	  || ! strcmp (language_string, "libgccjit")
 	 	+	  || ! strcmp (language_string, "vhdl"))
 	 	 	i = 0;