HDBC-Postgresql on Snow Leopard

The Problem

After upgrading to a new Mac Mini (running Snow Leopard on a 64-bit architecture), I installed the Haskell Platform. I then used cabal to install HDBC and HDBC-postgresql. I used Homebrew to install PostgreSQL. Everything installed fine.

I compiled a small Haskell script I'd been writing on my old Mac (32-bit architecture). It compiled fine, but when I ran a script that tried connecting to PostgreSQL, I got the following error.

can't load .so/.DLL for: pq (dlopen(/usr/local/Cellar/postgresql/8.4.4/lib/libpq.dylib, 9): no suitable image found.  Did find:
/usr/local/Cellar/postgresql/8.4.4/lib/libpq.dylib: mach-o, but wrong architecture)

Obviously, there was a problem with 32 vs 64 bit architectures. libpq, which I had built on the 64-bit machine, was a 64-bit build:

$ file /usr/local/Cellar/postgresql/8.4.4/lib/libpq.5.2.dylib
/usr/local/Cellar/postgresql/8.4.4/lib/libpq.5.2.dylib: Mach-O 64-bit dynamically linked shared library x86_64

but GHC was 32-bit:

$ file /Library/Frameworks/GHC.framework/Versions/612/usr/lib/ghc-6.12.3/ghc
/Library/Frameworks/GHC.framework/Versions/612/usr/lib/ghc-6.12.3/ghc: Mach-O executable i386

Incidentally, 64-bit builds of GHC on OS X are still pending.

Failed Attempts

My first thought was to simply rebuild PostgreSQL as a universal binary. That way Haskell could load the 32-bit version it needed and everything else could stay 64-bit. I knew that Perl was a universal binary:

$ file /usr/bin/perl
/usr/bin/perl: Mach-O universal binary with 3 architectures
/usr/bin/perl (for architecture x86_64):        Mach-O 64-bit executable x86_64
/usr/bin/perl (for architecture i386):  Mach-O executable i386
/usr/bin/perl (for architecture ppc7400):       Mach-O executable ppc

According to perl -V, the necessary CFLAGS and LDFLAGS options are -arch i386 -arch x86_64 -arch ppc. Several attempts invoking Homebrew with those options in the environment failed. I came across some tips about building a PostgreSQL universal binary. I tried several variations of his latest build script, but wasn't able to make it work.

The tricks for building a universal binary seemed easy enough, so I decided to modify the Homebrew formula using those tricks. In the process, I discovered that Homebrew has a convenient way for enabling universal builds within a formula. Just add to the formula the line:

ENV.universal_binary if ARGV.include? '--universal'

and universal binaries are built automatically. Even with this change (and rebuilding OSSP-UUID as a universal binary), I still got compiler errors when building PostgreSQL. The problem appeared to be the way that certain macros were expanded when compiling for multiple architectures.

Final Solution

At this point, I gave up on building from source. I came across the handy PostgreSQL installer for OS X. It installs a 32-bit version of PostgreSQL. After the installation, I linked libpq into /usr/local/lib and now everything works fine:

cd /usr/local/lib
ln -s /Library/PostgreSQL/8.4/lib/libpq.5.2.dylib  libpq.dylib

Although I might encounter problems down the road without a 64-bit PostgreSQL, this solution got me past the roadblock and taught me a lot about compiling for multiple architectures.