.. _BUILD:

Building GHDL from Sources
##########################

.. toctree::
   :hidden:

   Sources
   mcode
   LLVM
   GCC

GHDL can be downloaded as a `tarball <https://github.com/ghdl/ghdl/archive/master.tar.gz>`__/`zipfile <https://github.com/ghdl/ghdl/archive/master.zip>`__
or cloned with ``git clone`` from GitHub. GitHub offers HTTPS and SSH as transfer protocols. See the :ref:`SOURCES` page for
further details.

.. IMPORTANT::
   Since GHDL is written in `Ada`, independently of the code generator
   you use, a compiler is required. Most GNU/Linux package managers
   provide ``gcc-ada`` or ``gcc-gnat`` (which could be outdated).
   MSYS2 also provides ``gcc-ada`` for `MinGW64` and `UCRT64`.

.. ATTENTION::
   Since ``v0.37``, GHDL's synthesis features require GCC >=8.1, due to some new GNAT features which are not available in
   previous releases.

GHDL currently supports three different back-ends (code generators):

* mcode - built-in in-memory x86 (or x86_64) code generator
* GCC - Gnu Compiler Collection (`gcc.gnu.org <http://gcc.gnu.org/>`_)
* LLVM - Low-Level Virtual Machine (`llvm.org <http://llvm.org/>`_)

Here is a short comparison, so that you can choose the one you want to use:

+----------------------------+----------------------------------------------------------------------------+---------------------------------------------------------+
| Back-end                   | Pros                                                                       | Cons                                                    |
+============================+============================================================================+=========================================================+
| :ref:`mcode <BUILD:mcode>` | * Very easy to build                                                       | * Simulation is slower                                  |
|                            | * Very quick analysis                                                      | * x86_64/i386 only                                      |
|                            | * Can handle very large designs                                            |                                                         |
|                            | * Base simulation time can be modified for speeding up execution           |                                                         |
+----------------------------+----------------------------------------------------------------------------+---------------------------------------------------------+
| :ref:`LLVM <BUILD:llvm>`   | * Generated code is faster                                                 | * Build is more complex than mcode                      |
|                            | * Generated code can be debugged (with ``-g``)                             |                                                         |
|                            | * Easier to build than GCC                                                 |                                                         |
|                            | * Ported to many platforms (x86, x86_64, armv7/aarch64)                    |                                                         |
+----------------------------+----------------------------------------------------------------------------+---------------------------------------------------------+
| :ref:`GCC <BUILD:gcc>`     | * Generated code is faster (particularly with ``-O`` or ``-O2``)           | * Build is even more complex                            |
|                            | * Generated code can be debugged (with ``-g``)                             | * Analysis can take time (particularly for large units) |
|                            | * Ported to many platforms (x86, x86_64, PowerPC, SPARC)                   | * Code coverage collection (``gcov``) is unique to GCC  |
+----------------------------+----------------------------------------------------------------------------+---------------------------------------------------------+

.. HINT ::
   The output of both GCC and LLVM is an executable file, but `mcode` does not generate any. Therefore, if using GCC/LLVM,
   the call with argument ``-r`` can be replaced with direct execution of the binary. See section :ref:`USING:QuickStart:Simulation`.

After making your choice, you can jump to the corresponding section.
However, we suggest you to read :ref:`BUILD:dir_structure` first, so that you
know where the content will be placed and which files are expected to be
created.

.. HINT ::
  In these instructions, the configure script is executed in the source directory; but you can execute in a different
  directory too, like this:

	.. CODE:: Bash

		$ mkdir ghdl-objs
		$ cd ghdl-objs
		$ ../path/to/ghdl/configure ...


.. HINT ::
  For MacOS 10.15 (Catalina), see :ghdlsharp:`1368` for workarounds to link failures.

TL;DR
=====

In order to follow the traditional way to ``configure`` and ``make``, you need an Ada compiler.

.. HINT::
  Depending on the OS and distribution you are using, you will also need to install some toolchain dependencies, such as
  ``zlib``.

To use mcode backend (easiest to build), in the GHDL base directory, configure and build:

.. code-block::

  $ ./configure --prefix=/usr/local
  $ make

At that place, you can already use the `ghdl_mcode` built in the directory. You can also install GHDL:

.. code-block::

  $ make install

That's all!

.. HINT::
  The executable is installed as 'ghdl' in ``/usr/local``. To install it to a different path, change the ``--prefix`` in the
  call to ``configure``. For example, on Windows, you may want to set it to ``--prefix=/c/Program Files (x86)/GHDL``.
