Translating on Windows
======================

RPython is supported on Windows platforms, starting with Windows 2000.
The following text gives some hints about how to translate a interpreter
written in RPython, using PyPy as an example.

PyPy supports only being translated as a 32bit program, even on
64bit Windows.  See at the end of this page for what is missing
for a full 64bit translation.

To build pypy-c you need a working python environment, and a C compiler.
It is possible to translate with a CPython 2.6 or later, but this is not
the preferred way, because it will take a lot longer to run – depending
on your architecture, between two and three times as long. So head to
`our downloads`_ and get the latest stable version.

Microsoft Visual Studio is preferred as a compiler, but there are reports
of success with the mingw32 port of gcc.

.. _our downloads: http://pypy.org/download.html


What Compiler to use and How to find it?
----------------------------------------
The first stumbling block when building something for Python on windows is
how to discover the path to the compiler, headers, and libraries. One can
install many versions of the MSVC compiler tools, from stand-alone build
tools to full blown Visual Studio IDE installations. Each of these use cases
put the compiler at different locations, and the layout changes from time to
time.

The ``distutils`` package, located in the stdlib, is the natural place to put
this discovery code, but it is frozen by the python version. The pip-
installable ``setuptools`` can move faster to adapt to new tools. So the first
thing that will happen after building PyPy is it will install pip and download
``setuptools``, then it will build the cffi modules used in stdlib.
PyPy has a chicken and egg problem: in order to compile something we need
``setuptools``, but in order to get ``setuptools`` we need pip which requires
``_ssl``, and ``_ssl`` must be compiled. So PyPy vendors in a copy of
``msvc.py`` in ``rpython/tools/setuptools_msvc.py``.

PyPy will prefer to compile with the latest MSVC compiler it can find, which is
a departure from CPython's desire to compile with Visual Studio 9.

Translating PyPy with Visual Studio
-----------------------------------

We routinely test translation of PyPy using Visual Studio 2019, MSVC160.
Other configurations may work as well.

The translation scripts will set up the appropriate environment variables
for the compiler, so you do not need to run vcvars before translation.
They will pick the most recent Visual Studio
compiler they can find.  In addition, the target architecture
(32 bits, 64 bits) is automatically selected.  A 32 bit build can only be built
using a 32 bit Python and vice versa. By default the interpreter is built using
the Multi-threaded DLL (/MD) runtime environment.

If you wish to override this detection method to use a different compiler
(mingw or a different version of MSVC):

* set up the PATH and other environment variables as needed
* set the `CC` environment variable to compiler exe to be used,
  for a different version of MSVC `SET CC=cl.exe`.

**Note:** The RPython translator does currently not support 64 bit Python, and
translation will fail in this case.

Python and a C compiler are all you need to build pypy, but it will miss some
modules that relies on third-party libraries.  See below how to get
and build them.

Please see the :doc:`non-windows instructions <build>` for more information, especially note
that translation is RAM-hungry. A standard translation requires around 4GB, so
special preparations are necessary, or you may want to use the method in the
notes of the `build instructions`_ to reduce memory usage at the price of a
slower translation::

    set PYPY_GC_MAX_DELTA=200MB
    pypy --jit loop_longevity=300 ../../rpython/bin/rpython -Ojit targetpypystandalone
    set PYPY_GC_MAX_DELTA=
    # This is done as part of translation
    PYTHONPATH=../.. ./pypy-c ../../lib_pypy/tools/build_cffi_imports.py

.. _build instructions: http://pypy.org/download.html#building-from-source

Preparing Windows for the large build
-------------------------------------

Normally 32bit programs are limited to 2GB of memory on Windows. It is
possible to raise this limit, to 3GB on Windows 32bit, and almost 4GB
on Windows 64bit.

On Windows 32bit, it is necessary to modify the system: follow
http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=9583842&linkID=9240617
to enable the "3GB" feature, and reboot. This step is not necessary on
Windows 64bit.

Then you need to execute::

    <path-to-visual>\vc\vcvars.bat
    editbin /largeaddressaware translator.exe

where ``translator.exe`` is the pypy.exe or cpython.exe you will use to
translate with. This is done by default during PyPy translation, so it should
Just Work.


Installing external packages
----------------------------

We uses a subrepository_ inside pypy to hold binary compiled versions of the
build dependencies for windows. As part of the `rpython` setup stage, environment
variables will be set to use these dependencies. The repository has a README
file on how to replicate, and a branch for each supported platform. You may run
the `get_externals.py` utility to checkout the proper branch for your platform
and PyPy version.

.. _subrepository:  https://bitbucket.org/pypy/externals

Using the mingw compiler
------------------------

You can compile an RPython program with the mingw compiler, using the
--cc=mingw32 option; gcc.exe must be on the PATH. If the -cc flag does not
begin with "ming", it should be the name of a valid gcc-derivative compiler,
i.e. x86_64-w64-mingw32-gcc for the 64 bit compiler creating a 64 bit target.

You probably want to set the CPATH, LIBRARY_PATH, and PATH environment
variables to the header files, lib or dlls, and dlls respectively of the
locally installed packages if they are not in the mingw directory heirarchy.


libffi for the mingw compiler
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To enable the _rawffi (and ctypes) module, you need to compile a mingw
version of libffi.  Here is one way to do this, wich should allow you to try
to build for win64 or win32:

#. Download and unzip a `mingw32 build`_ or `mingw64 build`_, say into c:\mingw
#. If you do not use cygwin, you will need msys to provide make,
   autoconf tools and other goodies.

    #. Download and unzip a `msys for mingw`_, say into c:\msys
    #. Edit the c:\msys\etc\fstab file to mount c:\mingw

#. Download and unzip the `libffi source files`_, and extract
   them in the base directory.
#. Run c:\msys\msys.bat or a cygwin shell which should make you
   feel better since it is a shell prompt with shell tools.
#. From inside the shell, cd to the libffi directory and do::

    sh ./configure
    make
    cp .libs/libffi-5.dll <somewhere on the PATH>

If you can't find the dll, and the libtool issued a warning about
"undefined symbols not allowed", you will need to edit the libffi
Makefile in the toplevel directory. Add the flag -no-undefined to
the definition of libffi_la_LDFLAGS

If you wish to experiment with win64, you must run configure with flags::

    sh ./configure --build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32

or such, depending on your mingw64 download.


hacking on PyPy with the mingw compiler
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Since hacking on PyPy means running tests, you will need a way to specify
the mingw compiler when hacking (as opposed to translating). As of
March 2012, --cc is not a valid option for pytest.py. However if you set an
environment variable CC to the compiler exe, testing will use it.

.. _mingw32 build: http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win32/Automated%20Builds
.. _mingw64 build: http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Automated%20Builds
.. _msys for mingw: http://sourceforge.net/projects/mingw-w64/files/External%20binary%20packages%20%28Win64%20hosted%29/MSYS%20%2832-bit%29
.. _libffi source files: http://sourceware.org/libffi/


What is missing for a full 64-bit translation
---------------------------------------------

The main blocker is that we assume that the integer type of RPython is
large enough to (occasionally) contain a pointer value cast to an
integer.  The simplest fix is to make sure that it is so, but it will
give the following incompatibility between CPython and PyPy on Win64:

CPython: ``sys.maxint == 2**31-1, sys.maxsize == 2**63-1``

PyPy: ``sys.maxint == sys.maxsize == 2**63-1``

...and, correspondingly, PyPy supports ints up to the larger value of
sys.maxint before they are converted to ``long``.  The first decision
that someone needs to make is if this incompatibility is reasonable.

Assuming that it is, the first thing to do is probably to hack *CPython*
until it fits this model: replace the field in PyIntObject with a ``long
long`` field, and change the value of ``sys.maxint``.  This might just
work, even if half-brokenly: I'm sure you can crash it because of the
precision loss that undoubtedly occurs everywhere, but try not to. :-)

Such a hacked CPython is what you'll use in the next steps.  We'll call
it CPython64/64.

It is probably not too much work if the goal is only to get a translated
PyPy executable, and to run all tests before translation.  But you need
to start somewhere, and you should start with some tests in
``rpython/translator/c/test/``, like ``test_standalone.py`` and
``test_newgc.py``: try to have them pass on top of CPython64/64.

Keep in mind that this runs small translations, and some details may go
wrong.  The most obvious one is to check that it produces C files that
use the integer type ``Signed`` --- but what is ``Signed`` defined to?
It should be equal to ``long`` on every other platform, but on Win64 it
should be something like ``long long``.

What is more generally needed is to review all the C files in
``rpython/translator/c/src`` for the word ``long``, because this means a
32-bit integer even on Win64.  Replace it with ``Signed`` most of the
times.  You can replace one with the other without breaking anything on
any other platform, so feel free to.

Then, these two C types have corresponding RPython types: ``rffi.LONG``
and ``lltype.Signed`` respectively.  The first should really correspond
to the C ``long``.  Add tests that check that integers cast to one
type or the other really have 32 and 64 bits respectively, on Win64.

Once these basic tests work, you need to review ``rpython/rlib/`` for
uses of ``rffi.LONG`` versus ``lltype.Signed``.  The goal would be to
fix some more ``LONG-versus-Signed`` issues, by fixing the tests --- as
always run on top of CPython64/64.  Note that there was some early work
done in ``rpython/rlib/rarithmetic`` with the goal of running all the
tests on Win64 on the regular CPython, but I think by now that it's a
bad idea.  Look only at CPython64/64.

The major intermediate goal is to get a translation of PyPy with ``-O2``
with a minimal set of modules, starting with ``--no-allworkingmodules``;
you need to use CPython64/64 to run this translation too.  Check
carefully the warnings of the C compiler at the end. By default, MSVC
reports a lot of mismatches of integer sizes as warnings instead of
errors.

Then you need to review ``pypy/module/*/`` for ``LONG-versus-Signed``
issues.  At some time during this review, we get a working translated
PyPy on Windows 64 that includes all ``--translationmodules``, i.e.
everything needed to run translations.  Once we have that, the hacked
CPython64/64 becomes much less important, because we can run future
translations on top of this translated PyPy.  As soon as we get there,
please *distribute* the translated PyPy.  It's an essential component
for anyone else that wants to work on Win64!  We end up with a strange
kind of dependency --- we need a translated PyPy in order to translate a
PyPy ---, but I believe it's ok here, as Windows executables are
supposed to never be broken by newer versions of Windows.

Happy hacking :-)
