1=================================================================== 2How To Build On ARM 3=================================================================== 4 5Introduction 6============ 7 8This document contains information about building/testing LLVM and 9Clang on an ARM machine. 10 11This document is *NOT* tailored to help you cross-compile LLVM/Clang 12to ARM on another architecture, for example an x86_64 machine. To find 13out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`. 14 15Notes On Building LLVM/Clang on ARM 16===================================== 17Here are some notes on building/testing LLVM/Clang on ARM. Note that 18ARM encompasses a wide variety of CPUs; this advice is primarily based 19on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips. 20 21#. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the 22 Pandaboard, have become hard-float platforms. There are a number of 23 choices when using CMake. Autoconf usage is deprecated as of 3.8. 24 25 Building LLVM/Clang in ``Release`` mode is preferred since it consumes 26 a lot less memory. Otherwise, the building process will very likely 27 fail due to insufficient memory. It's also a lot quicker to only build 28 the relevant back-ends (ARM and AArch64), since it's very unlikely that 29 you'll use an ARM board to cross-compile to other arches. If you're 30 running Compiler-RT tests, also include the x86 back-end, or some tests 31 will fail. 32 33 .. code-block:: bash 34 35 cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \ 36 -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64" 37 38 Other options you can use are: 39 40 .. code-block:: bash 41 42 Use Ninja instead of Make: "-G Ninja" 43 Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True" 44 Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/install" 45 CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS) 46 47 After that, just typing ``make -jN`` or ``ninja`` will build everything. 48 ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For 49 running the test suite, please refer to :doc:`TestingGuide`. 50 51#. If you are building LLVM/Clang on an ARM board with 1G of memory or less, 52 please use ``gold`` rather then GNU ``ld``. In any case it is probably a good 53 idea to set up a swap partition, too. 54 55 .. code-block:: bash 56 57 $ sudo ln -sf /usr/bin/ld /usr/bin/ld.gold 58 59#. ARM development boards can be unstable and you may experience that cores 60 are disappearing, caches being flushed on every big.LITTLE switch, and 61 other similar issues. To help ease the effect of this, set the Linux 62 scheduler to "performance" on **all** cores using this little script: 63 64 .. code-block:: bash 65 66 # The code below requires the package 'cpufrequtils' to be installed. 67 for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do 68 sudo cpufreq-set -c $cpu -g performance 69 done 70 71 Remember to turn that off after the build, or you may risk burning your 72 CPU. Most modern kernels don't need that, so only use it if you have 73 problems. 74 75#. Running the build on SD cards is ok, but they are more prone to failures 76 than good quality USB sticks, and those are more prone to failures than 77 external hard-drives (those are also a lot faster). So, at least, you 78 should consider to buy a fast USB stick. On systems with a fast eMMC, 79 that's a good option too. 80 81#. Make sure you have a decent power supply (dozens of dollars worth) that can 82 provide *at least* 4 amperes, this is especially important if you use USB 83 devices with your board. Externally powered USB/SATA harddrives are even 84 better than having a good power supply. 85