System.Environment.getExecutablePath doesn't return absolute path to executable in OpenBSD. This happens because getExecutablePath uses argv[0] to determine path and argv[0] might not be absolute path.

My environment:

$ uname -a
OpenBSD fizbuz.pilkki.ciz.fi 6.0 GENERIC.MP#2274 amd64
$ ghc -V
The Glorious Glasgow Haskell Compilation System, version 7.10.3

This test program in OpenBSD:

module Main where
import System.Environment
main = getExecutablePath >>= print

returns

$ ./test
"./test"

For example in OS X the call returns absolute path:

$ ./test
"/Users/oherrala/tmp/test"

OpenBSD is one of the operating systems which gets fall back to using argv[0] to determine exec's location:

https://git.haskell.org/ghc.git/blob/HEAD:/libraries/base/System/Environment/ExecutablePath.hsc\#l152

Maybe the argv[0] result should be wrapped with realpath(3) to get absolute path?

This bug is also present in cabal-install and reported here: https://github.com/haskell/cabal/issues/3512\#issuecomment-231604356