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 #. If you are building LLVM/Clang on an ARM board with 1G of memory or less, 22 please use ``gold`` rather then GNU ``ld``. 23 Building LLVM/Clang with ``--enable-optimized`` 24 is preferred since it consumes less memory. Otherwise, the building 25 process will very likely fail due to insufficient memory. In any 26 case it is probably a good idea to set up a swap partition. 27 28 #. If you want to run ``make check-all`` after building LLVM/Clang, to avoid 29 false alarms (e.g., ARCMT failure) please use at least the following 30 configuration: 31 32 .. code-block:: bash 33 34 $ ../$LLVM_SRC_DIR/configure --with-abi=aapcs-vfp 35 36 #. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the 37 Pandaboard, have become hard-float platforms. The following set 38 of configuration options appears to be a good choice for this 39 platform: 40 41 .. code-block:: bash 42 43 ./configure --build=armv7l-unknown-linux-gnueabihf \ 44 --host=armv7l-unknown-linux-gnueabihf \ 45 --target=armv7l-unknown-linux-gnueabihf --with-cpu=cortex-a9 \ 46 --with-float=hard --with-abi=aapcs-vfp --with-fpu=neon \ 47 --enable-targets=arm --enable-optimized --enable-assertions 48 49 #. ARM development boards can be unstable and you may experience that cores 50 are disappearing, caches being flushed on every big.LITTLE switch, and 51 other similar issues. To help ease the effect of this, set the Linux 52 scheduler to "performance" on **all** cores using this little script: 53 54 .. code-block:: bash 55 56 # The code below requires the package 'cpufrequtils' to be installed. 57 for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do 58 sudo cpufreq-set -c $cpu -g performance 59 done 60 61 #. Running the build on SD cards is ok, but they are more prone to failures 62 than good quality USB sticks, and those are more prone to failures than 63 external hard-drives (those are also a lot faster). So, at least, you 64 should consider to buy a fast USB stick. On systems with a fast eMMC, 65 that's a good option too. 66 67 #. Make sure you have a decent power supply (dozens of dollars worth) that can 68 provide *at least* 4 amperes, this is especially important if you use USB 69 devices with your board. 70
