Mobile Haskell User Guide

Introduction

This is the accompanying User Guide for building mobile and embedded Haskell application using the The Glorious Glasgow Haskell Compilation System as a cross compiler.

Docker Image for Raspberry Pi

If your target is a Raspberry Pi image, you can use a pre-defined docker image instead of installing the toolchain on your local machine. You’ll still need to create a sysroot folder yourself, with the headers and libraries (see Making a Raspbian Cross Compilation SDK for more details).

With the sysroot ready, you can run the following command:

$ docker run -it -v /path/to/sysroot:/rpi/sysroot tritlo/ghc-to-rpi

To launch a docker container where you can cross-compile to your Raspberry Pi by running:

$ arm-linux-gnueabihf-ghc

For easy access, you can add -v $(pwd):/code to the docker launch command to have the current directory mounted to the /code directory in the container.

Installation

Pre-built binary distributions that target iOS (arm64, x86_64), Android (armv7, arm64, x86_64) as well as Raspberry Pi (armv6) for macOS Sierra and linux (deb8) can be dowloaded from http://hackage.mobilehaskell.org. Other architectures may be added at a later date but will for now be built from source. Using hadrian as the build system is highly recommended.

TODO: Document building from source.

The cross compiler use the LLVM code generator. As such an LLVM installation is required and needs to be in PATH. The LLVM toolchain provided by Xcode is insufficient as it does not provide the opt tool.

LLVM can be downloaded from http://releases.llvm.org/download.html#5.0.0. Extracting and adding the bin folder to PATH should be sufficient:

$ export PATH=/path/to/llvm/bin:$PATH

The pre built GHCs are relocatable, as such it is enough to simply extract them and add them to the PATH:

$ export PATH=/path/to/ghc-x86_64-apple-ios/bin:$PATH

To provide a unified interface over the cross compilers the general scheme of the tool chain is $target-tool, e.g. for ghc targeting aarch64-apple-ios, the tools are:

This unified interface is provided via the toolchain-wrappers for the pre-built cross compilers. After downloading the toolchain-wrappers, running the bootstrap.sh script and adjusting the linux-android-toolchain.config and raspberrypi-toolchain.config files to match the local Android NDK and Raspberry Pi SDK (TODO: building a raspberry pi SDK), the toolchain should be usable:

$ git clone https://github.com/zw3rk/toolchain-wrapper.git
$ (cd toolchain-wrapper && ./bootstrap)
$ export PATH=/path/to/toolchain-wrapper:$PATH

Troubleshooting

This section details a few known bugs.

Segfaults on Raspberry Pi

Anything that uses the time package directly or indirectly may unexpectedly segfault. It appears that the __tzfile_read function from glibc segfaults when called via tzset from GHC. The exact reasons why this happens are unknown right now. A suitable workaround is to set the TZ environment variable to a value that’s not a zonefile when launching the application. E.g. $ TZ="UTC0" ./Application.