[Mesa-dev] [RFC] Convert mesa to automake/libtool

[José Fonseca]

On Sun, 2010-05-02 at 09:46 -0700, Dan Nicholson wrote: 
> Brian,
> 
> I'm putting forward this request completely understanding your
> position why you don't want automake and libtool in your project.
> However, I think that mesa has outgrown the static Makefiles approach
> for a number of reasons. For a project that's grown to the complexity
> of mesa, I believe you need something that is more flexible and robust
> than the current system can provide. Eric (and I think Corbin, too)
> has a branch adding automake and libtool to the mesa repo.
> 
>   http://cgit.freedesktop.org/~anholt/mesa/log/?h=automake
> 
> I haven't looked at it in detail, but I know Eric knows what he's
> doing as he's maintained many of the autotooled xorg modules. Here are
> some of the pros and cons I see to making this change.
> 
> Pros:
> * AM_CONDITIONAL provides a clean way to separate optional parts of
> the build. The way that optional components are handled right now is
> pretty fragile and basically amounts to having lists of subdirectories
> being correct in the config file.
> 
> * For all mklib's simplicity, it is inconsistent between platforms,
> doesn't handle errors and provides only a scant amount of the features
> that libtool does. Libtool provides a robust and well tested means to
> generate libraries that handles nearly all the gory details about
> generating working binaries on many platforms. I don't think anyone
> working on mklib can claim to have the same type of knowledge about
> platforms and toolchains as the libtool developers.
> 
> * Consistency in build commands for free from automake. Right now we
> have the compiling and linking commands repeated throughout the tree
> and they're typically out of sync. I've tried to keep them in sync
> before and it was a lot of effort. With automake all you really need
> to do is tell it the CFLAGS and LIBS to use and it'll take care of the
> rest.
> 
> * Parallel make jobs just work. I've fixed so many of these race
> condition bugs, but they'd all just go away using automake. It has all
> the goop built in that people usually never think about.
> 
> * Well defined distribution for tarballs. The top-level Makefile does
> the job, but automake can make this a lot easier and more robust. It
> would also be simple to handle the generated files while also
> requiring they be included in the tarball.
> 
> * Fast source dependencies without external tools. The makedepend
> route works, but automake handles this in a faster, more robust and
> safer manner. We get a lot of people posting to the mailing list about
> build errors were the solution is "make realclean". This would solve a
> lot of those issues.
> 
> * Mindshare from xorg autotools. Many of the people here have and do
> work with the autotools via xorg, so it's not like this is a
> completely foreign beast.
> 
> * Moves the burden of build tool knowledge onto someone else. I don't
> think anyone here wants to become an expert on compilers, linkers and
> ABI for multiple platforms. It become a lot easier when you toss
> things off to libtool where people are actually spending their time
> caring about them.
> 
> * Extensive documentation available, unlike the current system which
> is pretty much ad hoc.
> 
> http://www.gnu.org/software/autoconf/manual/autoconf.html
> http://www.gnu.org/software/automake/manual/automake.html
> http://www.gnu.org/software/libtool/manual/libtool.html
> http://sourceware.org/autobook/autobook/autobook.html
> 
> Cons:
> * The abstracted nature of automake causes build debugging to be
> difficult. This requires you to train your brain not to look at the
> generated Makefile, but still it can be difficult. Fortunately, many
> of the build bugs we see today in Mesa would go away with automake.
> 
> * Using libtool means that you can't quickly hack around a fix for
> some platform. Fortunately, libtool is a lot more stable these days on
> common platforms.
> 
> * The maintainer (you) doesn't like it. Not much I can suggest here
> besides that it gets a lot easier the more you deal with it. And I'd
> be happy to help you out of any jams. For xorg, Peter Hutterer has
> asked me to solve a bunch of these problems, and I can't remember the
> last time we couldn't get something fixed.
> 
> * Loss of the simple "make $target" usage. I understand you guys use
> these targets to quickly pop out a build. As a compromise, we could
> turn the configs into wrapper scripts that generated the autotools
> files and ran configure with appropriate arguments. For example,
> "./configs/linux-debug && make". Or, since configure handles the
> platform parts, ./configs/debug or ./configs/osmesa.
> 
> That's all I can think of. I'm sure we can continue to make the
> current system work, but I think integrating these tools would be a
> big improvement. Thanks for considering it.

Geeze. One flame at a time..! :)

Now, seriously, my biggest regret with this direction is the missed
opportunity to use a single portable build system. We have part of Linux
developers using plain make, the other half and distros using autoconf,
and a few using scons; part of the windows developers using Visual
Studio projects, the others scons.

And although scons is not the holy grail of build systems, it is the
closest I know for Mesa/Gallium particular needs. Major showstopper for
automake/autoconf is that it requires cygwin/msys to be used on windows.
Also scons is extensible enough to do everything needed with a little of
python. scons' biggest drawbacks are that nobody else knows how to play
with it; and there are several things that don't come out of the box and
need to be customized.

So we keep trying to cater everybody needs by using the union of all
build systems instead of reaching a reasonable middle ground. But I've
resigned to the fact this is the sort of stuff that can never reach
consensus. It's like vi/emacs. :)

Jose