Build a custom Rust toolchain for Fuchsia

This guide explains how to build a Rust compiler for use with the Fuchsia. This is useful if you need to build Fuchsia with a patched compiler, or a compiler built with custom options. Building a custom Rust toolchain is not always necessary for building Fuchsia with a different version of Rust; see Build Fuchsia with a custom Rust toolchain for details.

Prerequisites

Prior to building a custom Rust toolchain for Fuchsia, you need to do the following:

  1. If you haven't already, clone the Rust source. The Guide to Rustc Development is a good resource to reference whenever you're working on the compiler.

    DEV_ROOT=DEV_ROOT  # parent of your Rust directory
git clone --recurse-submodules https://github.com/rust-lang/rust.git $DEV_ROOT/rust

  2. Run the following command to install cmake and ninja:

    sudo apt-get install cmake ninja-build

  3. Run the following command to obtain the infra sources:

    DEV_ROOT=DEV_ROOT  # parent of your Rust directory
mkdir -p "$DEV_ROOT/infra" && \
( \
  builtin cd "$DEV_ROOT/infra" && \
  jiri init && \
  jiri import -overwrite -name=fuchsia/manifest infra \
      https://fuchsia.googlesource.com/manifest && \
  jiri update \
)

  4. Run the following command to use cipd to get a Fuchsia core IDK, a Linux sysroot, a recent version of clang, and the correct beta compiler for building Fuchsia's Rust toolchain:

    DEV_ROOT=DEV_ROOT
HOST_TRIPLE=x86_64-unknown-linux-gnu
cat << "EOF" > ${DEV_ROOT}/cipd.ensure
fuchsia/third_party/clang/${platform} latest
fuchsia/third_party/cmake/${platform} integration
fuchsia/third_party/ninja/${platform} integration
fuchsia/third_party/make/${platform} version:4.3
infra/3pp/tools/go/${platform} version:3@1.24.1
@Subdir linux
fuchsia/third_party/sysroot/linux integration
@Subdir ubuntu20.04
fuchsia/third_party/sysroot/focal latest
@Subdir sdk
fuchsia/sdk/core/${platform} latest
@Subdir breakpad
fuchsia/tools/breakpad/${platform} integration
EOF
STAGE0_DATE=$(sed -nr 's/^compiler_date=(.*)/\1/p' ${DEV_ROOT}/rust/src/stage0)
STAGE0_VERSION=$(sed -nr 's/^compiler_version=(.*)/\1/p' ${DEV_ROOT}/rust/src/stage0)
STAGE0_COMMIT_HASH=$( \
  curl -s "https://static.rust-lang.org/dist/${STAGE0_DATE}/channel-rust-${STAGE0_VERSION}.toml" \
  | python3 -c 'import tomllib, sys; print(tomllib.load(sys.stdin.buffer)["pkg"]["rust"]["git_commit_hash"])')
echo "@Subdir stage0" >> cipd.ensure
echo "fuchsia/third_party/rust/host/\${platform} rust_revision:${STAGE0_COMMIT_HASH}" >> cipd.ensure
echo "fuchsia/third_party/rust/target/${HOST_TRIPLE} rust_revision:${STAGE0_COMMIT_HASH}" >> cipd.ensure
$DEV_ROOT/infra/fuchsia/prebuilt/tools/cipd ensure \
  --root "${DEV_ROOT}" \
  --ensure-file "${DEV_ROOT}/cipd.ensure"

    Downloading the Fuchsia-built stage0 compiler is optional, but useful for recreating builds in CI. If the stage0 is not available you may instruct the Rust build to download and use the upstream stage0 compiler by omitting those lines from your cipd.ensure file and removing the --stage0 arguments to generate_config.py below.

  5. Run the following command to build zlib.

    DEV_ROOT=DEV_ROOT  # parent of your Rust directory
CIPD_DIR=$DEV_ROOT/cipd
ZLIB_DIR="${DEV_ROOT}/zlib"
ZLIB_BUILD_DIR="${DEV_ROOT}/build/zlib"
ZLIB_INSTALL_DIR="${DEV_ROOT}/install/zlib"
if [[ ! -e  "$ZLIB_DIR" ]]; then
  git clone https://fuchsia.googlesource.com/third_party/zlib $ZLIB_DIR
fi
cd $ZLIB_DIR
git pull --ff-only
if [[ ! -e "${ZLIB_BUILD_DIR}" ]]; then
  mkdir -p "${ZLIB_BUILD_DIR}"
fi
if [[ ! -e "${ZLIB_INSTALL_DIR}" ]]; then
  mkdir -p "${ZLIB_INSTALL_DIR}"
fi
${CIPD_DIR}/bin/cmake \
  -S $ZLIB_DIR \
  -B $ZLIB_BUILD_DIR \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_MAKE_PROGRAM=${CIPD_DIR}/bin/ninja \
  -DCMAKE_INSTALL_PREFIX= \
  -DCMAKE_C_COMPILER=${CIPD_DIR}/bin/clang \
  -DCMAKE_CXX_COMPILER=${CIPD_DIR}/bin/clang++ \
  -DCMAKE_ASM_COMPILER=${CIPD_DIR}/bin/clang \
  -DCMAKE_LINKER=${CIPD_DIR}/bin/ld.lld \
  -DCMAKE_SYSROOT=${CIPD_DIR}/linux \
  -DCMAKE_AR=${CIPD_DIR}/bin/llvm-ar \
  -DCMAKE_NM=${CIPD_DIR}/bin/llvm-nm \
  -DCMAKE_OBJCOPY=${CIPD_DIR}/bin/llvm-objcopy \
  -DCMAKE_OBJDUMP=${CIPD_DIR}/bin/llvm-objdump \
  -DCMAKE_RANLIB=${CIPD_DIR}/bin/llvm-ranlib \
  -DCMAKE_READELF=${CIPD_DIR}/bin/llvm-readelf \
  -DCMAKE_STRIP=${CIPD_DIR}/bin/llvm-strip \
  -DCMAKE_SHARED_LINKER_FLAGS=-Wl,--undefined-version \
  -DCMAKE_C_FLAGS=--target=x86_64-linux-gnu \
  -DCMAKE_CXX_FLAGS=--target=x86_64-linux-gnu \
  -DCMAKE_ASM_FLAGS=--target=x86_64-linux-gnu
${CIPD_DIR}/bin/ninja \
  -C $ZLIB_BUILD_DIR
DESTDIR=$ZLIB_INSTALL_DIR ${CIPD_DIR}/bin/ninja \
  -C "$ZLIB_BUILD_DIR" \
  install

  6. Run the following command to build zstd.

    DEV_ROOT=DEV_ROOT  # parent of your Rust directory
CIPD_DIR=$DEV_ROOT/cipd
ZSTD_DIR=$DEV_ROOT/zstd
ZSTD_BUILD_DIR=$DEV_ROOT/build/zstd
ZSTD_INSTALL_DIR=$DEV_ROOT/install/zstd
if [[ ! -e "$ZSTD_DIR" ]]; then
  git clone https://fuchsia.googlesource.com/third_party/zstd $ZSTD_DIR
fi
cd $ZSTD_DIR
git pull --ff-only
if [[ ! -e "$ZSTD_BUILD_DIR" ]]; then
  mkdir -p "$ZSTD_BUILD_DIR"
fi
if [[ ! -e "$ZSTD_INSTALL_DIR" ]]; then
  mkdir -p "$ZSTD_INSTALL_DIR"
fi
$CIPD_DIR/bin/cmake \
  -S ${ZSTD_DIR}/build/cmake \
  -B $ZSTD_BUILD_DIR \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_MAKE_PROGRAM=$CIPD_DIR/bin/ninja \
  -DCMAKE_INSTALL_PREFIX= \
  -DCMAKE_C_COMPILER=$CIPD_DIR/bin/clang \
  -DCMAKE_CXX_COMPILER=$CIPD_DIR/bin/clang++ \
  -DCMAKE_ASM_COMPILER=$CIPD_DIR/bin/clang \
  -DCMAKE_LINKER=$CIPD_DIR/bin/ld.lld \
  -DCMAKE_SYSROOT=$CIPD_DIR/linux \
  -DCMAKE_AR=$CIPD_DIR/bin/llvm-ar \
  -DCMAKE_NM=$CIPD_DIR/bin/llvm-nm \
  -DCMAKE_OBJCOPY=$CIPD_DIR/bin/llvm-objcopy \
  -DCMAKE_OBJDUMP=$CIPD_DIR/bin/llvm-objdump \
  -DCMAKE_RANLIB=$CIPD_DIR/bin/llvm-ranlib \
  -DCMAKE_READELF=$CIPD_DIR/bin/llvm-readelf \
  -DCMAKE_STRIP=$CIPD_DIR/bin/llvm-strip \
  -DZSTD_BUILD_SHARED=OFF \
  -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
  -DCMAKE_C_FLAGS=--target=x86_64-linux-gnu \
  -DCMAKE_CXX_FLAGS=--target=x86_64-linux-gnu \
  -DCMAKE_ASM_FLAGS=--target=x86_64-linux-gnu
$CIPD_DIR/bin/ninja \
  -C $ZSTD_BUILD_DIR
DESTDIR=$ZSTD_INSTALL_DIR $CIPD_DIR/bin/ninja \
  -C $ZSTD_BUILD_DIR \
  install

Configure Rust for Fuchsia

  1. Change into your Rust directory.

  2. Run the following command to generate a configuration for the Rust toolchain:

    DEV_ROOT=DEV_ROOT
CIPD_DIR="${DEV_ROOT}/cipd"
ZLIB_INSTALL_DIR="${DEV_ROOT}/install/zlib"
ZSTD_INSTALL_DIR="${DEV_ROOT}/install/zstd"
STAGE0_DIR="${CIPD_DIR}/stage0"
( \
  export PATH="${DEV_ROOT}/infra/fuchsia/prebuilt/tools:$PATH" && \
  \
  $DEV_ROOT/infra/fuchsia/prebuilt/tools/vpython3 \
    $DEV_ROOT/infra/fuchsia/recipes/recipes/rust_toolchain.resources/generate_config.py \
      config_toml \
      --targets=aarch64-unknown-linux-gnu,x86_64-unknown-linux-gnu,thumbv6m-none-eabi,thumbv7m-none-eabi,riscv32imc-unknown-none-elf,riscv64gc-unknown-linux-gnu \
      --clang-prefix=$CIPD_DIR \
      --stage0="${STAGE0_DIR}" \
      --prefix="${DEV_ROOT}/install/fuchsia-rust" \
      --host-sysroot="${DEV_ROOT}/sysroot/linux" \
      --channel=nightly \
      --zlib-path="${ZLIB_INSTALL_DIR}" \
      --zstd-path="${ZSTD_INSTALL_DIR}" \
      --llvm-is-vanilla \
     | tee "${DEV_ROOT}/fuchsia-config.toml" && \
  \
  $DEV_ROOT/infra/fuchsia/prebuilt/tools/vpython3 \
      $DEV_ROOT/infra/fuchsia/recipes/recipes/rust_toolchain.resources/generate_config.py \
        environment \
        --targets=aarch64-unknown-linux-gnu,x86_64-unknown-linux-gnu,thumbv6m-none-eabi,thumbv7m-none-eabi,riscv32imc-unknown-none-elf,riscv64gc-unknown-linux-gnu \
        --source="${DEV_ROOT}/rust" \
        --stage0="${STAGE0_DIR}" \
        --clang-prefix="$${CIPD_DIR}" \
        --sdk-dir="${CIPD_DIR}/sdk" \
        --linux-sysroot="$CIPD_DIR}/linux" \
        --linux-riscv64-sysroot="${CIPD_DIR}/ubuntu20.04" \
        --eval \
     | tee "${DEV_ROOT}/fuchsia-env.sh" \
)

  3. (Optional) Run the following command to tell git to ignore the generated files:

    echo fuchsia-config.toml >> .git/info/exclude
echo fuchsia-env.sh >> .git/info/exclude

  4. (Optional) Customize fuchsia-config.toml.

Build and install Rust

  1. Change into your Rust source directory.

  2. Run the following command to build and install Rust plus the Fuchsia runtimes spec:

    DEV_ROOT=DEV_ROOT
rm -rf ${DEV_ROOT}/install/fuchsia-rust"
mkdir -p "${DEV_ROOT}/install/fuchsia-rust"
# Copy and paste the following subshell to build and install Rust, as needed.
# The subshell avoids polluting your environment with fuchsia-specific rust settings.
( \
  export CFLAGS="-I${DEV_ROOT}/install/zlib/include -I${DEV_ROOT}/install/zstd/include" && \
  export CXXFLAGS="-I${DEV_ROOT}/install/zlib/include -I${DEV_ROOT}/install/zstd/include" && \
  export LDFLAGS="-L${DEV_ROOT}/install/zlib/lib -L${DEV_ROOT}/install/zstd/lib" && \
  export RUSTFLAGS="-Clink-arg=-L${DEV_ROOT}/install/zlib/lib -Clink-arg=-L${DEV_ROOT}/install/zstd/lib" && \
  \
  source "${DEV_ROOT/fuchsia-env.sh" && \
  ./x.py install \
    --config "${DEV_ROOT}/fuchsia-config.toml" \
    --skip-stage0-validation \
 ) && \
 rm -rf "${DEV_ROOT}/install/fuchsia-rust/lib/.build-id" && \
 "${DEV_ROOT}/infra/fuchsia/prebuilt/tools/vpython3" \
  "${DEV_ROOT}/infra/fuchsia/recipes/recipes/rust_toolchain.resources/generate_config.py" \
    runtime \
  | "${DEV_ROOT}/infra/fuchsia/prebuilt/tools/vpython3" \
      "${DEV_ROOT}/infra/fuchsia/recipes/recipe_modules/toolchain/resources/runtimes.py" \
        --dir "${DEV_ROOT}/install/fuchsia-rust/lib" \
        --build-id-repo debug/.build-id \
        --readelf "${CIPD_DIR}/bin/llvm-readelf" \
        --dump_syms "${CIPD_DIR}/breakpad/dump_syms/dump_syms" \
        --objcopy "${CIPD_DIR}/bin/llvm-objcopy" \
        --dist dist \
  > "${DEV_ROOT}/install/fuchsia-rust/lib/runtime.json"

Build only (optional)

If you want to skip the install step, for instance during development of Rust itself, you can do so with the following command.

DEV_ROOT=DEV_ROOT
( \
  export CFLAGS="-I${DEV_ROOT}/install/zlib/include -I${DEV_ROOT}/install/zstd/include" && \
  export CXXFLAGS="-I${DEV_ROOT}/install/zlib/include -I${DEV_ROOT}/install/zstd/include" && \
  export LDFLAGS="-L${DEV_ROOT}/install/zlib/lib -L${DEV_ROOT}/install/zstd/lib" && \
  export RUSTFLAGS="-Clink-arg=-L${DEV_ROOT}/install/zlib/lib -Clink-arg=-L${DEV_ROOT}/install/zstd/lib" && \
  \
  source "${DEV_ROOT}fuchsia-env.sh && \
  \
  ./x.py build \
  --config \
    "${DEV_ROOT}/fuchsia-config.toml" \
    --skip-stage0-validation \
)

Troubleshooting

If you are getting build errors, try deleting the Rust build directory:

rm -rf fuchsia-build

Then re-run the command to build Rust.

Building Fuchsia with a custom Rust toolchain

With a newly compiled custom Rust toolchain, you're ready to use it to build Fuchsia. Directions on how to do so are available in a dedicated guide.