1 =================================================================== 2 How To Build On ARM 3 =================================================================== 4 5 Introduction 6 ============ 7 8 This document contains information about building/testing LLVM and 9 Clang on an ARM machine. 10 11 This document is *NOT* tailored to help you cross-compile LLVM/Clang 12 to ARM on another architecture, for example an x86_64 machine. To find 13 out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`. 14 15 Notes On Building LLVM/Clang on ARM 16 ===================================== 17 Here are some notes on building/testing LLVM/Clang on ARM. Note that 18 ARM encompasses a wide variety of CPUs; this advice is primarily based 19 on 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 ``Relese`` 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 $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \ 36 -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64" 37 38 Other options you can use are: 39 40 .. code-block:: bash 41 42 Use Ninja instead of Make: "-G Ninja" 43 Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True" 44 Force Python2: "-DPYTHON_EXECUTABLE=/usr/bin/python2" 45 Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/instal" 46 CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS) 47 48 After that, just typing ``make -jN`` or ``ninja`` will build everything. 49 ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For 50 running the test suite, please refer to :doc:`TestingGuide`. 51 52 #. If you are building LLVM/Clang on an ARM board with 1G of memory or less, 53 please use ``gold`` rather then GNU ``ld``. In any case it is probably a good 54 idea to set up a swap partition, too. 55 56 .. code-block:: bash 57 58 $ sudo ln -sf /usr/bin/ld /usr/bin/ld.gold 59 60 #. ARM development boards can be unstable and you may experience that cores 61 are disappearing, caches being flushed on every big.LITTLE switch, and 62 other similar issues. To help ease the effect of this, set the Linux 63 scheduler to "performance" on **all** cores using this little script: 64 65 .. code-block:: bash 66 67 # The code below requires the package 'cpufrequtils' to be installed. 68 for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do 69 sudo cpufreq-set -c $cpu -g performance 70 done 71 72 Remember to turn that off after the build, or you may risk burning your 73 CPU. Most modern kernels don't need that, so only use it if you have 74 problems. 75 76 #. Running the build on SD cards is ok, but they are more prone to failures 77 than good quality USB sticks, and those are more prone to failures than 78 external hard-drives (those are also a lot faster). So, at least, you 79 should consider to buy a fast USB stick. On systems with a fast eMMC, 80 that's a good option too. 81 82 #. Make sure you have a decent power supply (dozens of dollars worth) that can 83 provide *at least* 4 amperes, this is especially important if you use USB 84 devices with your board. Externally powered USB/SATA harddrives are even 85 better than having a good power supply. 86
