The story on OS X 10.6 with ghc-6.12 on x86 hardware seems to be this: Apple's gcc: Defaults to i386 or ppc on Mac OS X 10.5 and earlier, depending on the CPU type detected at runtime. On Mac OS X 10.6 the default is x86_64 if the CPU supports it, i386 otherwise. Passing -arch i386 or -arch x86_64 explicitly chooses the mode explicitly. Passing BOTH -arch i386 AND -arch x86_64 creates something special which is a universal binary that holds both versions in a single file. MacPorts: The provides an easy way to compile and install a plethora of mostly unix-y software from source. It handles the arch problem by allowing +universal to be specified when installing a package or set by default in /opt/local/etc/macports/variants.conf, which is what I have done. Without +universal the default arch can be specified in /opt/local/etc/macports/macports.conf. gtk: I have build gtk2-2.20.1 with macports as a universal library. ghc: Unlike ghc on Linux, ghc on OS X is not capable of creating x86_64 libraries and programs. Using ghc before 6.12 on OS X 10.6 used to require some small option hacks to explicitly set -arch i386. Now ghc is invoked directly. ( http://hackage.haskell.org/trac/ghc/ticket/2965 ) hsc2hs: On OS 10.6 ghc is calling hsc2hs without any special -arch option, and hsc2hs is calculating offsets in x86_64 mode. This is breaking the interface between ghc and c-structures for various libraries. In particular I ran into this with gtk2hs. It may suffice to get '--cc-flag=-m32 --ld-flag=-m32' to hsc2hs as a work around. While ticket #2965 is not yet fixed it would be better if hsc2hs understood the default arch on OS X 10.6 is not compatible with ghc. -- Chris On 08/06/2010 22:03, Axel Simon wrote:

Hi all,

we're facing serious problems (the seg'faulting kind) with Gtk2Hs on Mac OS 10.6. Chris has tracked this down to incorrect structure offsets that hsc2hs calculates.

The offsets that hsc2hs calculates are too large, so it is probably in x86_64 mode. The offsets with which Gtk+ was compiled are smaller, so it must have been compiled with something like -arch i386. My question is the following: What is the right way to compile unixy software on Mac OS 10.6. Is the Gtk+ library incorrectly compiled or is hsc2hs not producing its C file in the correct way? It seems that a C Gtk+ program works correctly when compiled with no special flags.

The only thing we could do is to pass some magic option to hsc2hs when it creates the C program that calculates the offsets. Detecting how Gtk+ was compiled would require some sort of autoconf magic which is beyond a simple cabal file. So I probably cannot hope for an easy fix.

Any comments or experience appreciated, cheers, Axel