| =================================================================== | |
| How To Build On ARM | |
| =================================================================== | |
| Introduction | |
| ============ | |
| This document contains information about building/testing LLVM and | |
| Clang on an ARM machine. | |
| This document is *NOT* tailored to help you cross-compile LLVM/Clang | |
| to ARM on another architecture, for example an x86_64 machine. To find | |
| out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`. | |
| Notes On Building LLVM/Clang on ARM | |
| ===================================== | |
| Here are some notes on building/testing LLVM/Clang on ARM. Note that | |
| ARM encompasses a wide variety of CPUs; this advice is primarily based | |
| on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips. | |
| #. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the | |
| Pandaboard, have become hard-float platforms. There are a number of | |
| choices when using CMake. Autoconf usage is deprecated as of 3.8. | |
| Building LLVM/Clang in ``Relese`` mode is preferred since it consumes | |
| a lot less memory. Otherwise, the building process will very likely | |
| fail due to insufficient memory. It's also a lot quicker to only build | |
| the relevant back-ends (ARM and AArch64), since it's very unlikely that | |
| you'll use an ARM board to cross-compile to other arches. If you're | |
| running Compiler-RT tests, also include the x86 back-end, or some tests | |
| will fail. | |
| .. code-block:: bash | |
| cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \ | |
| -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64" | |
| Other options you can use are: | |
| .. code-block:: bash | |
| Use Ninja instead of Make: "-G Ninja" | |
| Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True" | |
| Force Python2: "-DPYTHON_EXECUTABLE=/usr/bin/python2" | |
| Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/instal" | |
| CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS) | |
| After that, just typing ``make -jN`` or ``ninja`` will build everything. | |
| ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For | |
| running the test suite, please refer to :doc:`TestingGuide`. | |
| #. If you are building LLVM/Clang on an ARM board with 1G of memory or less, | |
| please use ``gold`` rather then GNU ``ld``. In any case it is probably a good | |
| idea to set up a swap partition, too. | |
| .. code-block:: bash | |
| $ sudo ln -sf /usr/bin/ld /usr/bin/ld.gold | |
| #. ARM development boards can be unstable and you may experience that cores | |
| are disappearing, caches being flushed on every big.LITTLE switch, and | |
| other similar issues. To help ease the effect of this, set the Linux | |
| scheduler to "performance" on **all** cores using this little script: | |
| .. code-block:: bash | |
| # The code below requires the package 'cpufrequtils' to be installed. | |
| for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do | |
| sudo cpufreq-set -c $cpu -g performance | |
| done | |
| Remember to turn that off after the build, or you may risk burning your | |
| CPU. Most modern kernels don't need that, so only use it if you have | |
| problems. | |
| #. Running the build on SD cards is ok, but they are more prone to failures | |
| than good quality USB sticks, and those are more prone to failures than | |
| external hard-drives (those are also a lot faster). So, at least, you | |
| should consider to buy a fast USB stick. On systems with a fast eMMC, | |
| that's a good option too. | |
| #. Make sure you have a decent power supply (dozens of dollars worth) that can | |
| provide *at least* 4 amperes, this is especially important if you use USB | |
| devices with your board. Externally powered USB/SATA harddrives are even | |
| better than having a good power supply. |