cabal-install infers the wrong $arch/$os when used with a cross-compiler

[simonmar]

I want to install packages using cabal with a GHC cross-compiler, and have them installed into .cabal/lib/$arch-$os/... so that they don't conflict with my native packages. Unfortunately, cabal uses the host rather than the target $arch-$os, so the cross-compiled packages will conflict with my native packages.

In my ~/.cabal/config I have

install-dirs user
  libsubdir: $arch-$os/$pkgid/$compiler

where my local $arch-$os is x86_64-linux and the target is arm-linux.

$ cabal install --with-ghc=$HOME/code/ghc-pi/inplace/bin/ghc-stage1 --with-ld=$HOME/tmp/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-ld parallel --reinstall
Resolving dependencies...
Configuring parallel-3.2.0.3...
Building parallel-3.2.0.3...
Preprocessing library parallel-3.2.0.3...
...
Registering parallel-3.2.0.3...
Installing library in
/home/simon/.cabal/lib/x86_64-linux/parallel-3.2.0.3/ghc-7.7.20130117
Registering parallel-3.2.0.3...

The correct target platform could be obtained by passing --info to the GHC named in --with-ghc.

[23Skidoo]

Currently, the values from System.Info are always used for $arch and $os. To fix this, we need to make initialPathTemplateEnv take a Platform parameter and add a way to get a Platform given a CompilerId and a ProgramDb (for GHC, this means parsing ghc --info).

[singpolyma]

Can I suggest that, once this is supported, it become the default setting for libsubdir, with similar defaults for datasubdir and docs?

[singpolyma]

This also causes packages like primitive to fail to install under a cross-compiler, because they use arch tests to enable certain gcc flags.

[23Skidoo]

@singpolyma Good point. The target platform should be also used instead of the host platform in conditions.

[the-real-blackh]

I've done some work on this at https://github.com/ghc-ios/packages-Cabal because I'm going to need this for cross-compiling to iOS to work properly.

[the-real-blackh]

This patch https://gist.github.com/the-real-blackh/4983885 adds --host-os=XX and --host-arch=XX options, and also an OS called "ios". I need this functionality for the iOS cross-compile changes in ghc.

It doesn't specifically address the naming of the directory as .cabal/lib/$arch-$os/..., but this would be easy to add to what I've already done.

[tibbe]

@the-real-blackh Would you mind creating a pull request once you think the code is ready so we can review it? Thanks!

[the-real-blackh]

Thanks for that. I've decided that the only proper way to do it would be to do what Simon M says and extract the hostOS and hostArch automatically from the selected ghc. So I'll work on that and prepare a pull request.

[lukexi]

Hi guys, on behalf of @the-real-blackh and I here's a pull request addressing this. #1210

[23Skidoo]

#1214 should have fixed this. Feel free to reopen.