annotate docs/HowToBuildOnARM.rst @ 95:afa8332a0e37 LLVM3.8

LLVM 3.8
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Tue, 13 Oct 2015 17:48:58 +0900
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1 ===================================================================
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2 How To Build On ARM
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3 ===================================================================
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5 Introduction
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6 ============
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8 This document contains information about building/testing LLVM and
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9 Clang on an ARM machine.
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11 This document is *NOT* tailored to help you cross-compile LLVM/Clang
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12 to ARM on another architecture, for example an x86_64 machine. To find
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13 out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`.
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15 Notes On Building LLVM/Clang on ARM
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16 =====================================
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17 Here are some notes on building/testing LLVM/Clang on ARM. Note that
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18 ARM encompasses a wide variety of CPUs; this advice is primarily based
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19 on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips.
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21 #. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
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22 please use ``gold`` rather then GNU ``ld``.
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23 Building LLVM/Clang with ``--enable-optimized``
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24 is preferred since it consumes less memory. Otherwise, the building
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25 process will very likely fail due to insufficient memory. In any
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26 case it is probably a good idea to set up a swap partition.
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28 #. If you want to run ``make check-all`` after building LLVM/Clang, to avoid
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29 false alarms (e.g., ARCMT failure) please use at least the following
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30 configuration:
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31
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32 .. code-block:: bash
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34 $ ../$LLVM_SRC_DIR/configure --with-abi=aapcs-vfp
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36 #. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the
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37 Pandaboard, have become hard-float platforms. The following set
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38 of configuration options appears to be a good choice for this
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39 platform:
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41 .. code-block:: bash
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43 ../$LLVM_SRC_DIR/configure --build=armv7l-unknown-linux-gnueabihf \
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44 --host=armv7l-unknown-linux-gnueabihf \
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45 --target=armv7l-unknown-linux-gnueabihf --with-cpu=cortex-a9 \
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46 --with-float=hard --with-abi=aapcs-vfp --with-fpu=neon \
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47 --enable-targets=arm --enable-optimized --enable-assertions
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49 #. ARM development boards can be unstable and you may experience that cores
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50 are disappearing, caches being flushed on every big.LITTLE switch, and
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51 other similar issues. To help ease the effect of this, set the Linux
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52 scheduler to "performance" on **all** cores using this little script:
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53
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54 .. code-block:: bash
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56 # The code below requires the package 'cpufrequtils' to be installed.
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57 for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do
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58 sudo cpufreq-set -c $cpu -g performance
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59 done
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61 #. Running the build on SD cards is ok, but they are more prone to failures
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62 than good quality USB sticks, and those are more prone to failures than
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63 external hard-drives (those are also a lot faster). So, at least, you
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64 should consider to buy a fast USB stick. On systems with a fast eMMC,
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65 that's a good option too.
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66
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67 #. Make sure you have a decent power supply (dozens of dollars worth) that can
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68 provide *at least* 4 amperes, this is especially important if you use USB
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69 devices with your board.