[Haskell-beginners] GHC-generated executables size

[Daniel Fischer]

On Saturday 16 October 2010 12:26:00, . wrote:
> Hi,
> I was playing around with ghc again, and I was wondering what makes
> the executables so large and how I could make them smaller (strip works,
> but is there anything more I can do?)
> More specifically, I am compiling a program that uses the GTK+ bindings,
> HDBC, and some things from Prelude.
> The program simply displays a window, and reads and writes values
> from/into a data base file. Not much, really.
> Anyway, the program size is 20MB without stripping, and 10MB after
> stripping ...
>
> Any hints?

Two things spring to mind (in addition to the static linking mentioned by 
Aleksandar).

1) If you didn't compile the packages with -split-objs, when you use one 
function from a module, the entire object file for the module is linked in.
For packages with many modules or many dependencies, that adds up pretty 
fast.

If you set
                                                 
split-objs: True

in your ~/.cabal/config, packages installed via cabal-install (the cabal 
executable) will be built with -split-objs and only the needed functions 
will be linked in (at least if you compile your programmes with 
optimisations, I don't know whether -O0 uses split object files or the 
monolithic ones).
(Downside: building the packages takes longer, duh; and you need more disk 
space for monolithic+split object files, duh again).

2) If it's not (only) that,
it's probably the same effect as discussed in
http://hackage.haskell.org/trac/ghc/ticket/4387

Simon (PJ) says:
"Every module has a module-initialisation routine. Apart from initialising 
the module, it calls the module-initialisation routine for each imported 
module. So if M imports module SpecConstr from package ghc, then the 
module-initialisatin routine for M will call the initialisation routine for 
SpecConstr. Even though nothing from SpecConstr is ultimately used."

So if you import a module (you don't even need to use anything from it) 
which transitively imports a lot of modules, you get a ton of module-
initialisation routines.
People are thinking about how to handle this best (since it affects the 
vector package, on which a lot of other packages depend, it's not 
unimportant).

>
> Thanks and good night for now ..
> Christian
>