Why can't I install any packages with GHC 7.8.4 on Raspberry Pi?

Question

According to this post there is finally a debian package for a version of GHC that supports template haskell and ghci.

And this is true, I started from a fresh copy of Raspbian, I changed my /etc/apt/sources.list file to:

deb http://http.debian.net/debian sid main contrib non-free
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://archive.raspbian.org/raspbian/ wheezy main contrib non-free rpi

I did sudo apt-get update && sudo apt-get upgrade, and then I did sudo apt-get install ghc and sudo apt-get install cabal-install.

ghc --version reports 7.8.4. GHCi works just fine, and so does TH.

But for some reason I can't install any packages with cabal. No matter which one I pick, I get some version of this error:

login as: pi
[email protected]'s password: 
Linux raspberrypi 3.18.11-v7+ #781 SMP PREEMPT Tue Apr 21 18:07:59 BST 2015 armv7l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Mon May 11 17:17:22 2015

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.4
$ mkdir test
$ cd test
$ cabal sandbox init
Writing a default package environment file to
/home/pi/test/cabal.sandbox.config
Creating a new sandbox at /home/pi/test/.cabal-sandbox
$ cabal install array
Resolving dependencies...
Notice: installing into a sandbox located at /home/pi/test/.cabal-sandbox
Downloading array-0.5.1.0...
Configuring array-0.5.1.0...
Failed to install array-0.5.1.0
Build log ( /home/pi/test/.cabal-sandbox/logs/array-0.5.1.0.log ):
cabal: Error: some packages failed to install:
array-0.5.1.0 failed during the configure step. The exception was:
user error ('/usr/bin/ghc' exited with an error:
/tmp/ghc2287_0/ghc2287_6.s: Assembler messages:

/tmp/ghc2287_0/ghc2287_6.s:76:0:
Error: selected processor does not support ARM mode `movw
r7,:lower16:stg_bh_upd_frame_info'

/tmp/ghc2287_0/ghc2287_6.s:77:0:
Error: selected processor does not support ARM mode `movt
r7,:upper16:stg_bh_upd_frame_info'

/tmp/ghc2287_0/ghc2287_6.s:80:0:
Error: selected processor does not support ARM mode `movw
r7,:lower16:base_GHCziTopHandler_runMainIO_closure'

/tmp/ghc2287_0/ghc2287_6.s:81:0:
Error: selected processor does not support ARM mode `movt
r7,:upper16:base_GHCziTopHandler_runMainIO_closure'

/tmp/ghc2287_0/ghc2287_6.s:82:0:
Error: selected processor does not support ARM mode `movw
r8,:lower16:Cabalzm1zi22zi1zi1_DistributionziSimple_defaultMain_closure'

/tmp/ghc2287_0/ghc2287_6.s:83:0:
Error: selected processor does not support ARM mode `movt
r8,:upper16:Cabalzm1zi22zi1zi1_DistributionziSimple_defaultMain_closure'
)

Does anyone know where I went off the rails?

Update

$ cabal --version
cabal-install version 1.22.0.1
using version 1.22.1.1 of the Cabal library

Answer 1

It needs --ghc-options=-opta-march=armv7a as an option every time you want to build something with GHC or cabal install something. With this, it works!

Update

If instead you do --ghc-options="-opta-mcpu=cortex-a7 -opta-mfpu=neon -opta-mtune=native -opta-mfloat-abi=hard, floating point will work too. I arrived at this by guessing-and-checking and reading old forum posts, so its possible that these too are not the best settings.

Cabal also has a user configuration file where you can store this setting and have it applied whenever GHC is invoked.