using ghc with make
simonmarhaskell at gmail.com
Tue Apr 18 06:37:12 EDT 2006
Frederik Eaton wrote:
> I have a project which currently uses Cabal, and I would like to
> switch to using a plain Makefile.
> I have two examples of projects that use Makefiles, darcs and jhc, but
> they both appear to hand-code the list of dependencies for
> executables. The "-M" option to ghc should let us do this
> automatically, but either because of a deficiency in GHC or in GNU
> Make, that looks to be impossible or difficult. Does anyone have
> experience with this?
Yes, GHC's build system works like this. We don't use --make at all
when building GHC itself. However, I want to switch to using Cabal to
build the libraries. Eventually I envisage using Cabal to build more
parts of the GHC tree.
There's certainly no reason that you can't use ghc -M with GNU make, and
that's something we will continue to support. What problems are you having?
> Since I'm not using the multi-compiler features of Cabal, I think it
> shouldn't be too hard to get the project-specific part of my Makefile
> down to the size of the .cabal file.
Sure, but you also have a quite a lot of build system infrastructure to
get right. Incedentally, this is exactly what Cabal was meant to avoid.
> - I want to be able to rebuild specific targets, rather than building
> everything every time
Multiple Cabal packages tied together with a simple Makefile could do
> - I want better dependency inference, for instance I don't want to
> relink every executable every time I do a build (I think this is fixed
> in newer versions of ghc, but not the one I use)
Yes, fixed in 6.4.2
The comments about --make are interesting: ceratinly we're aware that it
has a scalability problem, and it certainly isn't conducive to a
frequent edit/compile/test cycle, which is one reason we don't use it in
GHC. However, for a straight single-CPU build, from scratch, for a
large program, and if you have a lot of memory, it is much faster than
make. I don't have figures for GHC to hand, but I believe it is on the
order of a factor of 2 or 3. I would expect 'make -j4' to definitely
win on a 4-core box. We do have experimental patches for GHC to make
--make work across multiple CPUs too, but you don't get linear speedup
(single-threaded GC is one bottleneck).
I think it would be prudent at some point to make Cabal build without
--make and to add multiprocessor support.
FWIW, I don't think 'ghc -c Foo.hs Bar.hs' goes any faster than
separately compiling the two files, it doesn't cache anything between
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