# Compiling LLVM on RISC-V

By simply copying & pasting the following, absolutely verbatim with no
changes, you can get a working clang from the head of the official llvm
master branch. I've tested it on a completely virgin install of Ubuntu
16.04 LTS server. It should work on other versions of Ubuntu and on
other Debian-based distros. (If it doesn't then please let me know)

Note that you currently must use a soft float version of the rv32 compiler
and libraries.

You can skip the gnu toolchain and/or qemu parts if you already have
those.

    # about 17 GB of disk space is needed
    # entire process takes (not including apt-get, which is about 90 seconds on AWS):
    #   87m10s on i7-8650U Intel NUC with 32 GB RAM (on 30 Mbps VDSL internet in NZ)
    #   20m40s on server with Xeon E5-2667v4 @3.20GHz (16 cores)
    #   17m30s on an AWS m5.12xlarge with fresh Ubuntu 16.04 AMI (ami-4e79ed36)

    #harmless if things are already installed. Obviously you can't do it if
    #you're not an admin
    sudo apt-get update
    sudo apt-get -y dist-upgrade
    sudo apt-get -y install \
      binutils build-essential libtool texinfo \
      gzip zip unzip patchutils curl git \
      make cmake ninja-build automake bison flex gperf \
      grep sed gawk python bc \
      zlib1g-dev libexpat1-dev libmpc-dev \
      libglib2.0-dev libfdt-dev libpixman-1-dev 

    mkdir riscv
    cd riscv
    mkdir _install
    export PATH=`pwd`/_install/bin:$PATH

    git clone --recursive https://github.com/riscv/riscv-gnu-toolchain
    pushd riscv-gnu-toolchain
    ./configure --prefix=`pwd`/../_install --with-arch=rv32gc --with-abi=ilp32
    make -j`nproc`
    popd

    git clone https://github.com/riscv/riscv-qemu
    pushd riscv-qemu
    ./configure --prefix=`pwd`/../_install --target-list=riscv32-linux-user
    make -j`nproc` install
    popd

    git clone https://github.com/llvm-project/llvm-project-20170507 llvm
    pushd llvm
    (cd llvm/tools; ln -s ../../clang .) 
    mkdir _build
    cd _build
    cmake -G Ninja -DCMAKE_BUILD_TYPE="Release" \
      -DBUILD_SHARED_LIBS=True -DLLVM_USE_SPLIT_DWARF=True \
      -DLLVM_OPTIMIZED_TABLEGEN=True -DLLVM_BUILD_TESTS=False \
      -DDEFAULT_SYSROOT="../../_install/riscv32-unknown-elf" \
      -DGCC_INSTALL_PREFIX="../../_install" \
      -DLLVM_DEFAULT_TARGET_TRIPLE="riscv32-unknown-elf" \
      -DLLVM_TARGETS_TO_BUILD="" \
      -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="RISCV" \
      ../llvm
    cmake --build .
    alias clang-rv32="`pwd`/bin/clang -Xclang -iwithsysroot -Xclang /include \
      -ccc-gcc-name riscv32-unknown-elf-gcc \
      -target riscv32 -march=rv32imc"
    popd

    cat >hello.c <<END
    #include <stdio.h>

    int main(){
      printf("Hello RISCV!\n");
      return 0;
    }
    END

    clang-rv32 -O1 hello.c -o hello
    qemu-riscv32 hello