Ensure that you have a copy of bison and flex installed on your system. All major systems should have these tools installed or available in package management systems.

$ bison --version
GNU Bison version 1.28
$ flex --version
flex version 2.5.4

Check out a copy of LLVM SVN, and build a release build (as opposed to a debug one). Currently, due to Issue 70, we are limited to revision 42498.

svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm-svn -r 42498
pushd llvm-svn
./configure --enable-optimized
make ENABLE_OPTIMIZED=1
sudo make install
LLVMOBJDIR=`pwd`
popd

Check out a copy of the iphone-dev SVN repository.

svn checkout http://iphone-dev.googlecode.com/svn/trunk/ iphone-dev
pushd iphone-dev

Make a directory to hold the toolchain.

sudo mkdir /usr/local/arm-apple-darwin

mkdir -p build/odcctools
pushd build/odcctools
../../odcctools/configure --target=arm-apple-darwin --disable-ld64
export INCPRIVEXT="-isysroot /Developer/SDKs/MacOSX10.4u.sdk"
make
sudo make install
popd

Get a copy of the iPhone root filesystem. This is usually obtained by decrypting and extracting the iPhone restore software using these tools, but there are many other methods to obtain this, including simply using scp to download all the files from the iPhone over Wi-Fi.

To unpack the root filesystem, mount the dmg, open terminal and run

sudo mkdir /usr/local/share/iphone-filesystem
sudo cp -Rp /Volumes/Snowbird3A110a.N45Bundle/* /usr/local/share/iphone-filesystem/

Now, set the environment variable $HEAVENLY to its path:

HEAVENLY=/usr/local/share/iphone-filesystem

pushd include
./configure --with-macosx-sdk=/Developer/SDKs/MacOSX10.4u.sdk
sudo bash install-headers.sh
popd

Install csu, which includes crt1.o, dylib1.o, and bundle1.o. Don't rebuild them from source, as this requires a working cross-GCC, which you don't have yet (and the build-from-source process for csu is broken right now anyway). Binaries are provided for this reason.

mkdir -p build/csu
pushd build/csu
../../csu/configure --host=arm-apple-darwin
sudo make install
popd

Make sure that $LLVMOBJDIR and $HEAVENLY are set per the instructions above.

mv llvm-gcc-4.0-iphone/configure llvm-gcc-4.0-iphone/configure.old
sed 's/^FLAGS_FOR_TARGET=$/FLAGS_FOR_TARGET=${FLAGS_FOR_TARGET-}/g' llvm-gcc-4.0-iphone/configure.old > llvm-gcc-4.0-iphone/configure
sudo ln -s /usr/local/arm-apple-darwin/lib/crt1.o \/usr/local/arm-apple-darwin/lib/crt1.10.5.o
mkdir -p build/llvm-gcc-4.0-iphone
pushd build/llvm-gcc-4.0-iphone
export FLAGS_FOR_TARGET="-mmacosx-version-min=10.1"
sh ../../llvm-gcc-4.0-iphone/configure --enable-llvm=`llvm-config --obj-root` \
--enable-languages=c,c++,objc,obj-c++ --target=arm-apple-darwin --enable-sjlj-exceptions \
--with-heavenly=$HEAVENLY --with-as=/usr/local/bin/arm-apple-darwin-as \
--with-ld=/usr/local/bin/arm-apple-darwin-ld
make LLVM_VERSION_INFO=2.0-svn-iphone-dev-0.3-svn
sudo make install
popd
popd

You're done. Have fun!

- drudge