-
Notifications
You must be signed in to change notification settings - Fork 13
Building Clang with eBPF Target for ARC HS Hosts
If you want to build eBPF programs right on the target, then you need to properly build Clang for ARC. There is no need for all possible targets, so we are going to build Clang with support of eBPF target only.
It's necessary to install the latest available development tools for CentOS 7
to make it possible to build clang. Use centos-release-scl repository
to install the latest tools and enable them:
.. code-block:: bash
sudo yum install centos-release-scl
sudo yum install devtoolset-9
scl enable devtoolset-9 bash
Also llvm build system requires new CMake. Install cmake3 packages
and use it instead of cmake:
.. code-block:: bash
sudo yum install cmake3
llvm build system requires new CMake. To install it on Ubuntu 18.04
you can use cmake package provided by CMake's team:
Prepare sources:
.. code-block:: bash
git clone https://github.com/llvm/llvm-project.git
mkdir llvm-project/build
cd llvm-project/build
Prepare build system using CMake:
.. code-block:: bash
cmake -DCMAKE_INSTALL_PREFIX=/tools/clang-bpf \
-DLLVM_ENABLE_PROJECTS=clang \
-DLLVM_TARGETS_TO_BUILD=BPF \
-DLLVM_INCLUDE_BENCHMARKS=OFF \
-DLLVM_ENABLE_PIC=ON \
-DLLVM_ENABLE_WARNINGS=OFF \
-DLLVM_ENABLE_ZLIB=OFF \
-DLLVM_INCLUDE_EXAMPLES=OFF \
-DLLVM_INCLUDE_TESTS=OFF \
-DCMAKE_BUILD_TYPE=Release \
-G "Unix Makefiles" \
../llvm
Build and install to /tools/clang-bpf:
.. code-block:: bash
make -j $(nproc)
make install
Prepare sources:
.. code-block:: bash
git clone https://github.com/llvm/llvm-project.git
mkdir llvm-project/build
cd llvm-project/build
Clang's build system (CMake) uses a toolchain file for configuring cross-compiler.
Suppose that the toolchain for ARC HS 4x is placed in /tools/arc-linux-gnu
(the directory which contains bin). Save this configuration to ~/arc.cmake:
.. code-block:: cmake
SET(CMAKE_SYSTEM_NAME Linux)
SET(CMAKE_HOST_SYSTEM_PROCESSOR arc)
SET(CMAKE_HOST_SYSTEM_PROCESSOR Linux)
SET(CMAKE_HOST_SYSTEM_PROCESSOR gnu)
SET(CMAKE_SYSTEM_VERSION 1)
SET(CMAKE_C_COMPILER /tools/arc-linux-gnu/bin/arc-linux-gnu-gcc)
SET(CMAKE_CXX_COMPILER /tools/arc-linux-gnu/bin/arc-linux-gnu-g++)
SET(CMAKE_FIND_ROOT_PATH /tools/arc-linux-gnu/sysroot)
# Search for programs in the build host directories
SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
# ... for libraries and headers in the target directories
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
SET(HAVE_POSIX_REGEX 0)
SET(HAVE_STEADY_CLOCK 0)
Prepare build system using CMake:
.. code-block:: bash
cmake -DCMAKE_TOOLCHAIN_FILE=~/arc.cmake \
-DCMAKE_INSTALL_PREFIX=/tools/clang-bpf-arc \
-DLLVM_ENABLE_PROJECTS=clang \
-DLLVM_TARGETS_TO_BUILD=BPF \
-DCMAKE_BUILD_TYPE=MinSizeRel \
-DLLVM_INCLUDE_BENCHMARKS=OFF \
-DLLVM_ENABLE_PIC=ON \
-DBUILD_SHARED_LIBS=ON \
-DLLVM_ENABLE_WARNINGS=OFF \
-DLLVM_ENABLE_ZLIB=OFF \
-DLLVM_INCLUDE_EXAMPLES=OFF \
-DLLVM_INCLUDE_TESTS=OFF \
-DCMAKE_EXE_LINKER_FLAGS="-latomic" \
-DCMAKE_MODULE_LINKER_FLAGS="-latomic" \
-DCMAKE_SHARED_LINKER_FLAGS="-latomic" \
-G "Unix Makefiles" \
../llvm
Explanation for some options:
-
-DCMAKE_BUILD_TYPE=MinSizeRel- Turn on optimizations for size. -
-DLLVM_INCLUDE_BENCHMARKS=OFF- Turn off benchmarks to avoid fails while building. -
-DBUILD_SHARED_LIBS=ON- Don't build Clang as one large blob (more than 100 MB) because linker cannot resolve relocations for such large binaries. -
-DCMAKE_***_LINKER_FLAGS="-latomic"- Somehow-latomicis not passed to the linker while building. Thus we need to pass it manually.
Build and install to /tools/clang-bpf-arc:
.. code-block:: bash
make -j $(nproc)
make install
Then you can copy this directory to your target (e.g., to the overlay for Buildroot).