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annotate docs/HowToBuildOnARM.rst @ 107:a03ddd01be7e

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author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Sun, 31 Jan 2016 17:34:49 +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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4
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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 #. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the
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22 Pandaboard, have become hard-float platforms. There are a number of
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23 choices when using CMake. Autoconf usage is deprecated as of 3.8.
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25 Building LLVM/Clang in ``Relese`` mode is preferred since it consumes
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26 a lot less memory. Otherwise, the building process will very likely
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27 fail due to insufficient memory. It's also a lot quicker to only build
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28 the relevant back-ends (ARM and AArch64), since it's very unlikely that
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29 you'll use an ARM board to cross-compile to other arches. If you're
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30 running Compiler-RT tests, also include the x86 back-end, or some tests
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31 will fail.
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33 .. code-block:: bash
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34
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35 cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \
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36 -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64"
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37
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38 Other options you can use are:
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39
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40 .. code-block:: bash
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41
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42 Use Ninja instead of Make: "-G Ninja"
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43 Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True"
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44 Force Python2: "-DPYTHON_EXECUTABLE=/usr/bin/python2"
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45 Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/instal"
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46 CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS)
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47
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48 After that, just typing ``make -jN`` or ``ninja`` will build everything.
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49 ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For
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50 running the test suite, please refer to :doc:`TestingGuide`.
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51
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52 #. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
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53 please use ``gold`` rather then GNU ``ld``. In any case it is probably a good
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54 idea to set up a swap partition, too.
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55
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56 .. code-block:: bash
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57
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58 $ sudo ln -sf /usr/bin/ld /usr/bin/ld.gold
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60 #. ARM development boards can be unstable and you may experience that cores
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61 are disappearing, caches being flushed on every big.LITTLE switch, and
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62 other similar issues. To help ease the effect of this, set the Linux
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63 scheduler to "performance" on **all** cores using this little script:
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64
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65 .. code-block:: bash
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67 # The code below requires the package 'cpufrequtils' to be installed.
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68 for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do
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69 sudo cpufreq-set -c $cpu -g performance
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70 done
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71
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72 Remember to turn that off after the build, or you may risk burning your
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73 CPU. Most modern kernels don't need that, so only use it if you have
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74 problems.
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75
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76 #. Running the build on SD cards is ok, but they are more prone to failures
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77 than good quality USB sticks, and those are more prone to failures than
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78 external hard-drives (those are also a lot faster). So, at least, you
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79 should consider to buy a fast USB stick. On systems with a fast eMMC,
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80 that's a good option too.
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81
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82 #. Make sure you have a decent power supply (dozens of dollars worth) that can
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83 provide *at least* 4 amperes, this is especially important if you use USB
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84 devices with your board. Externally powered USB/SATA harddrives are even
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85 better than having a good power supply.