Cross Compile GHC for iOS

Scripts and notes on cross-compiling The Glasgow Haskell Compiler on macOS x86_64 targeting iOS (device [aarch64/arm64] and simulator [x86_64]) with the goal of writing iOS applications in (largely) Haskell.

Why

As Apple goes farther and farther into custom silicon, LLVM/bitcode, Swift and other requirements for iOS applications, GHC's built-in support for iOS is getting weaker and weaker. There seems to have been a flurry of interest around using Haskell on iOS around 2017, but I had a hard time finding more recent resources.

I am trying to see if I can create a non-trivial application in (largely) Haskell that Apple will accept on the iOS App Store.

The landscape will likely change very soon with the M1 chip and everything needing to support the LLVM/Clang/aarch64 toolchain if they want to run on new Macs.

Why Haskell

The farther into my career I get, the more I appreciate typed programming languages. Also, working with more and more programming languages, they are all kinda doing the same thing in different ways. Let's just use one language.

TL;DR

At the end of the day, this repo does three things:

1. Patch GHC's source code with some things (See ./ios.patch)
2. Invoke GHC's ./configure with some specific environment variables set (See ghc_prepare in ./start)
3. Provides a Haskell library and Xcode project to test everything with

This was developed/tested on:

• macOS Big Sur (11.5.2)
• Xcode 13.0 (13A233)
• iOS 15
  • iPhone 12 Pro (real device)
  • iPhone 12 Pro (simulator)

Quick Start

Overall, we are:

1. Installing dependencies
2. Setup toolchain wrappers for use by GHC's autotools/make
3. Cross-compiling GHC for device (aarch64/arm64) and iOS simulator (x86_64)
4. Building Haskell lib for use by XCode/Swift iOS app
5. Setup Xcode/Swift project to use build Haskell library
6. Run on simulator!
7. Run on device!

#
# DEPENDENCIES
#

# You need to be on macOS, have Xcode and Homebrew installed

# brew install automake llvm ghc cabal-install 
./start deps 

# create toolchain wrappers for automake
./start toolchain

#
# GHC
#

# Clean build x86_64-apple-ios (simulator)
# Or can specify aarch64-apple-ios (device)
./start ghc all x86_64-apple-ios 2>&1 | tee ghc.$(date +%F_%T).log

#
# HASKELL
#

# Build Haskell staticlib for x86_64-apple-ios (simulator)
# Or can specify aarch64-apple-ios (device)
./start haskell build x86_64-apple-ios

The ./start script is just a helper. See ghc_patch and ghc_prepare in ./start for the details.

Setup Xcode Project

You can use the provided iOS project at test/ios-project or follow these steps for a new project:

1. Create Swift/SwiftUI iOS App
2. Add bridging header
3. Add external references to bridging header
4. Init Haskell in App.init
5. Add "Other Linker Flags": -lhs
6. Add "Library Search Paths": $(SRCROOT)/<PATH>/build/hs-libs/$(CURRENT_ARCH)
7. Add libiconv.tbd to Frameworks

Press play!

HELP!

Something went wrong!

Yeah, this is all pretty new. A lot of us are trying to figure this out and Apple is always changing...everything.

Try these steps out to get a clear error message to report. Once you have this, feel free to file a bug. Maybe someone can help, or at the very least you'll have a clear repro so that you can try to fix yourself!

# setup environment variables with toolchain wrappers in the PATH
eval "$(./start bash)"

# go into the GHC source dir
cd build/ghc-8.10.7

# make everything that builds successfully so we can see the error more easily
make -kj

# make with no-parallelism so you can get a consistent error message
make -j1
# alternatively pipe it into a log file or sublime
# make -j1 2>&1 | tee debug.log
# make -j1 2>&1 | subl

GHC's make files are pretty complicated. Make's --print-data-base shows what command is invoked for each target. NOTE that GHC's make files are setup to run multiple times (one for each phase).

make --print-data-base

Links

References:

• https://medium.com/@zw3rk/a-haskell-cross-compiler-for-ios-7cc009abe208
• https://github.com/nanotech/swift-haskell-tutorial/blob/master/README.md
• https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/shared_libs.html
• https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/9.0.1-notes.html#highlights
• https://github.com/zw3rk/toolchain-wrapper
• https://medium.com/@zw3rk/ghcs-cross-compilation-pipeline-ac88972466ec
• Rust on iOS
• nanotech/swift-haskell-tutorial

TODO

• Build and run on simulator
• Build and run on device
• Parameterize which version to build (x86_64 vs aarch64)
• Create 'all' targets to do everything
• How to clear allocated memory
• Will Apple accept an Haskell project?
• Do we need libffi anymore?
• Add test suite
• explain aarch64 and arm64

Debugging afterwards

pushd build/ghc-8.10.7
make -kj
make -j1 2>&1 | subl

---

Open Questions

• alex
  • provided with source distributions, if we used GIT, we would need to install these
• happy
  • provided with source distributions, if we used GIT, we would need to install these
• Patched
  • execToWritable
  • clock_getcpuclockid
  • llvm_targets

Debugging Bitcode

Trying to figure out where to put bitcode flags in this massive Makefile situation...

utils/hp2ps/dist-install/build/AreaBelow.o w/o Bitcode

command rm utils/hp2ps/dist-install/build/AreaBelow.o make -pdC utils/hp2ps 2>&1 | tee debug.log

commands to execute (from `utils/hp2ps/ghc.mk', line 44):

$(call cmd,utils/hp2ps_dist-install_CC) $(utils/hp2ps_dist-install_$(utils/hp2ps_dist-install_PROGRAM_WAY)_ALL_CC_OPTS) -c $< -o $@

$(utils/hp2ps_dist-install_CC) = $(CC_STAGE1) $(CC_STAGE1) = $(CC)

$(utils/hp2ps_dist-install_$(utils/hp2ps_dist-install_PROGRAM_WAY)_ALL_CC_OPTS)

$(utils/hp2ps_dist-install_PROGRAM_WAY) = v

utils/hp2ps_dist-install_v_ALL_CC_OPTS = $(WAY_$(utils/hp2ps_dist-install_PROGRAM_WAY)CC_OPTS) $(utils/hp2ps_dist-install_DIST_GCC_CC_OPTS) $(utils/hp2ps_dist-install$(utils/hp2ps_dist-install_PROGRAM_WAY)_CC_OPTS) $($(basename $<)_CC_OPTS) $(utils/hp2ps_dist-install_EXTRA_CC_OPTS) $(EXTRA_CC_OPTS) $(if $(findstring YES,$(utils/hp2ps_dist-install_SplitSections)),-ffunction-sections -fdata-sections)

utils/hp2ps_dist-install_$(utils/hp2ps_dist-install_PROGRAM_WAY)_CC_OPTS = utils/hp2ps_dist-install_v_CC_OPTS =

WAY_$(utils/hp2ps_dist-install_PROGRAM_WAY)_CC_OPTS = WAY_v_CC_OPTS =

utils/unlit/dist-install/build/unlit.o w/o Bitcode

$(call cmd,utils/unlit_dist-install_CC) $(utils/unlit_dist-install_$(utils/unlit_dist-install_PROGRAM_WAY)_ALL_CC_OPTS) -c $< -o $@

utils/unlit_dist-install_$(utils/unlit_dist-install_PROGRAM_WAY)ALL_CC_OPTS = utils/unlit_dist-install_v_ALL_CC_OPTS = $(WAY$(utils/unlit_dist-install_PROGRAM_WAY)CC_OPTS) $(utils/unlit_dist-install_DIST_GCC_CC_OPTS) $(utils/unlit_dist-install$(utils/unlit_dist-install_PROGRAM_WAY)_CC_OPTS) $($(basename $<)_CC_OPTS) $(utils/unlit_dist-install_EXTRA_CC_OPTS) $(EXTRA_CC_OPTS) $(if $(findstring YES,$(utils/unlit_dist-install_SplitSections)),-ffunction-sections -fdata-sections)

$(utils/unlit_dist-install_$(utils/unlit_dist-install_PROGRAM_WAY)_CC_OPTS) = utils/unlit_dist-install_v_CC_OPTS

utils/hsc2hs/dist-install/build/cbits/utils.o w/o Bitcode

utils/hsc2hs_dist-install_$(utils/hsc2hs_dist-install_PROGRAM_WAY)_ALL_CC_OPTS = utils/hsc2hs_dist-install_v_ALL_CC_OPTS

libraries/base/dist-install/build/libHSbase-4.14.3.0.a(IO.o) w/o Bitcode

"inplace/bin/ghc-stage1" -o utils/hsc2hs/dist-install/build/tmp/hsc2hs -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall
-hide-all-packages -package-env - -i -iutils/hsc2hs/. -iutils/hsc2hs/dist-install/build -Iutils/hsc2hs/dist-install/build -iutils/hsc2hs/dist-install/build/hsc2hs/autogen -Iutils/hsc2hs/dist-install/build/hsc2hs/autogen -optP-include -optPutils/hsc2hs/dist-install/build/hsc2hs/autogen/cabal_macros.h -package-id base-4.14.3.0 -package-id containers-0.6.5.1 -package-id directory-1.3.6.0 -package-id filepath-1.4.2.1 -package-id process-1.6.13.2 -Wall -XHaskell2010 -no-user-package-db -rtsopts -Wnoncanonical-monad-instances -outputdir utils/hsc2hs/dist-install/build -static -O0 -H64m -Wall -hide-all-packages -package-env - -i -iutils/hsc2hs/. -iutils/hsc2hs/dist-install/build -Iutils/hsc2hs/dist-install/build -iutils/hsc2hs/dist-install/build/hsc2hs/autogen -Iutils/hsc2hs/dist-install/build/hsc2hs/autogen -optP-include -optPutils/hsc2hs/dist-install/build/hsc2hs/autogen/cabal_macros.h -package-id base-4.14.3.0 -package-id containers-0.6.5.1 -package-id directory-1.3.6.0 -package-id filepath-1.4.2.1 -package-id process-1.6.13.2 -Wall -XHaskell2010 -no-user-package-db -rtsopts -Wnoncanonical-monad-instances utils/hsc2hs/dist-install/build/Main.o utils/hsc2hs/dist-install/build/C.o utils/hsc2hs/dist-install/build/Common.o utils/hsc2hs/dist-install/build/CrossCodegen.o utils/hsc2hs/dist-install/build/DirectCodegen.o utils/hsc2hs/dist-install/build/Flags.o utils/hsc2hs/dist-install/build/HSCParser.o utils/hsc2hs/dist-install/build/ATTParser.o utils/hsc2hs/dist-install/build/UtilsCodegen.o utils/hsc2hs/dist-install/build/Compat/ResponseFile.o utils/hsc2hs/dist-install/build/Compat/TempFile.o utils/hsc2hs/dist-install/build/Paths_hsc2hs.o utils/hsc2hs/dist-install/build/cbits/utils.o

libraries/base/dist-install/build/libHSbase-4.14.3.0.a.contents command rm
libraries/base/dist-install/build/GHC/Conc/IO.o
libraries/base/dist-install/build/GHC/IO.o
libraries/base/dist-install/build/System/IO.o

"inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -this-unit-id base-4.14.3.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-prim-0.6.1 -package-id integer-simple-0.1.2.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -fllvm -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -outputdir libraries/base/dist-install/build -c libraries/base/./GHC/IO.hs -v -o libraries/base/dist-install/build/GHC/IO.o

"inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -this-unit-id base-4.14.3.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-prim-0.6.1 -package-id integer-simple-0.1.2.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -fllvm -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -outputdir libraries/base/dist-install/build -c libraries/base/./GHC/Conc/IO.hs -v -o libraries/base/dist-install/build/GHC/Conc/IO.o

"inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -this-unit-id base-4.14.3.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-prim-0.6.1 -package-id integer-simple-0.1.2.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -fllvm -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -outputdir libraries/base/dist-install/build -c libraries/base/./System/IO.hs -v -o libraries/base/dist-install/build/System/IO.o

"inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -this-unit-id base-4.14.3.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-prim-0.6.1 -package-id integer-simple-0.1.2.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -fllvm -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -outputdir libraries/base/dist-install/build -c libraries/base/./GHC/Conc/IO.hs -v -o libraries/base/dist-install/build/GHC/Conc/IO.o

command rm libraries/base/dist-install/build/GHC/Conc/IO.o "inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -this-unit-id base-4.14.3.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-prim-0.6.1 -package-id integer-simple-0.1.2.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -fllvm -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -outputdir libraries/base/dist-install/build -c libraries/base/./GHC/Conc/IO.hs -v -o libraries/base/dist-install/build/GHC/Conc/IO.o 2>&1 | subl -w

rts/dist/build/libCffi.a

libffi/build/inst/lib/libffi.a