Dec 11, 2007

Jhbuild Adventures on Windows

Background: I'm going home to my parents house for Christmas, and because I don't have a laptop, I thought it would be the perfect opportunity to use their computer to get Conduit working on windows. However I could not find windows builds of (py)goocanvas anywhere. Never minding a challenge I thought it would be a good experiment to see if I could build pygoocanvas for windows via cross-compilation or natively - both using jhbuild.

I like to think that F/OSS works because people keep re-inventing the wheel in new and obscure ways everytime they do something, so what follows is my rambling tale of cross-compiling-gtk-for-windows wheel reinvention.

Cross compiling Gtk+ for Windows using Jhbuild

Starting with the work of Alberto Ruiz and Piotr Gaczkowski I thought I would setup a jhbuild environment to cross compile the Gtk+ stack. After a bit of fiddling I managed to get everything to build fine using mingw32 and jhbuild. The following files work successfully on Ubuntu gutsy and can build the latest stable releases of Gtk+/cairo/glib/libglade.

At this point I moved onto trying to build pygobject. This is where things got difficult. I tried a few different ways to get the cross compilation environment to see python. With some inspiration from this page on compiling glom for windows, I copied across the entire Python25 directory from a windows box and added it to the appropriate LDFLAGS and CFLAGS in jhbuild. This allowed pygobject to pass configure. However it now failed to build;

In file included from /usr/include/python2.5/Python.h:57,
    from pygobject.h:5,
    from pygobject-private.h:9,
    from gobjectmodule.c:27:
    /usr/include/python2.5/pyport.h:246:24: sys/select.h: No such file or directory

I went back to the windows machine and checked to see if sys/select.h was present in mingw. No luck. OK at this point I was stuck. Compiling wasn't looking likely, and I still wasnt even confident that if it did compile it would manange to actually link and run (due to different compiler versions and platforms, etc). I googled for a bit and saw that its now possible to build python extensions using mingw32 and that people had managed to cross compile python using mingw. Hmm, I pondered..... 'lets cross compile Python25 using mingw and then build pygobject using that.' Furthur googling revealed this python bug+patch for cross compiling using mingw. This is going to be easy.......

I added a new section to my modules file that would apply the patch to the Python 2.5.1 before building it. YOU FAIL AGAIN JOHN.

checking for %zd printf() format support... configure: error: cannot run test program while cross compiling

Hmm. I tried several strategies to get around this (including supplying a config.cache file with ac_cv_printf_zd_format=yes) but with no luck. You can see my plea for help on the bug report.......

At this point an entire day of my life had been irrevocably taken from me. I retired to bed. I would not let windows beat me....

Native compilation of Gtk+ for Windows using Jhbuild

OK. At this point I thought I might as well start again, but compile natively on windows using mingw and msys. In hindsight it probbably would have been easier to follow most of the instructions for glom verbaim, but I decided to continue my quest at wheel re-invention.

I read that Alberto was thinking about ways to make Jhbuild work on windows - a good goal. Starting with his patch on that bug report I modified it slightly so that tar, gunzip and friends wouldn't need to be installed. Furthur to that I set about hacking up some patches to allow jhbuild to at least run on windows. A few hours later and I was sure that this was going to take a few more hours :-). I now had a working (ish) minimal easy to set up windows build environment according to these instructions..... or so I thought.

Jhbuild managed to successfully parse my minimal jhbuildrc and module files, download and untar iconv but then it failed. Basically there is considerable work and thought needed to see how this should operate in msys/cygwin. The problem is already explained in part here, but I will summarise.

Python's os.path and friends do a good job at converting paths to the native system format. Unfortunately the msys and cygwin shells also convert paths. For instance msys automagically converts /foo/bar to C:\msys\foo\bar. Basically it means that python converts paths to windows format, but msys likes them in unix format (because its a unix shell environment). This results in files not getting found, and gross composite paths like --prefix=C:\foo\bar/baz/bob getting passed to configure.

So, I had a bit of a look at how this could be solved in Jhbuild. I guess there are a few strategies

  1. Create a whole bunch of utility functions join_path(), prepend_path(), etc. And call these instead of the system ones and only escape to windows format if you are running in windows, and not running in windows just kidding you are really running in cygwin haha.

  2. Remove all os.path and friends calls. Be really naive and hard code all path operations to use unix semantics. Then explictly note that Jhbuild on windows must be run from within a unix shell like msys/bash or cygwin/bash.

  3. Magic. Come up with some sort of paranormal event that would win GNOME $1 million dollars which could then pay a developer to fix all this for me.


Well things didn't work out as well as I hoped. I will probbably go and compile everything without jhbuild and be happy. I did learn that;

  • Jhbuild on windows is a worthwhile cause. It would really help in automatically (jhautobuild) testing things like glib and GIO (at least giving devs a compile yes/no signal)

  • It could make generating the latest tarballs really easy, perhaps even sharing the same modulesets as those maintained by the release team

  • For extra bling it could even automatically create installers by tracking installed files using a strategy similar to checkinstall.

Help, thoughts or advice appreciated. For all the luck I have had the last few days I would not be surprised if I have missed something fundamentally obvious to this whole process. Heck if some fairy was to drop a pygoocanvas installer for windows in my mail box then I would be super happy. Oh and did I mention that im really looking forward to gio!