One of my goals with this project is to produce code that can run with no external dependencies across as much of our Unix estate as possible. That is several thousand machines, tho’ I am only interested in a few hundred of those. This would be a complete non-issue on a grown-up platform like SPARC but unfortunately we have jumped aboard the Linux bandwagon, so it is not entirely straightforward.

Consider just about the simplest possible Haskell program:

debian$ cat Hello.hs
module Main where main = putStrLn "Hello, world!"
debian$ ghc --make Hello.hs
debian$ ./Hello
Hello, world!

All well and good on my 32-bit Debian PC, but the same binary on 32-bit CentOS:

centos$ ./Hello
Hello: timer_create: Invalid argument

Hmm. Some research reveals that perhaps this can be addressed with different compilation options:

debian$ ghc --make Hello.hs -threaded

centos$ ./Hello
Hello, world!

Jolly good. But on 64-bit Redhat, which is the main target environment:

redhat64$ ./Hello
./Hello: error while loading shared libraries: libffi.so.5: cannot open shared object file: No such file or directory

Hmm some more. Now the sensible thing to do would just be to either convince the sysadmins to install FFI everywhere or just deploy my own build (for each target?!) along with my binaries. Or indeed to just install GHC! But the strategy is to minimize dependencies, even on LD_LIBRARY_PATH, so let’s try:

debian$ ghc --make Hello.hs -optl-static -optl-pthread
debian$ ./Hello
Hello, world!

And now:

redhat64$ ./Hello
Hello, world!

Perfect! But unfortunately:

centos$ ./Hello
FATAL: kernel too old
Segmentation fault

Erm, lol? I’m with jwz. But since Debian is my development environment and RHEL is my target, I can live with it.