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===================================================================
How To Build On ARM
===================================================================
Introduction
============
This document contains information about building/testing LLVM and
Clang on an ARM machine.
This document is *NOT* tailored to help you cross-compile LLVM/Clang
to ARM on another architecture, for example an x86_64 machine. To find
out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`.
Notes On Building LLVM/Clang on ARM
=====================================
Here are some notes on building/testing LLVM/Clang on ARM. Note that
ARM encompasses a wide variety of CPUs; this advice is primarily based
on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips.
#. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
please use ``gold`` rather then GNU ``ld``.
Building LLVM/Clang with ``--enable-optimized``
is preferred since it consumes less memory. Otherwise, the building
process will very likely fail due to insufficient memory. In any
case it is probably a good idea to set up a swap partition.
#. If you want to run ``make check-all`` after building LLVM/Clang, to avoid
false alarms (e.g., ARCMT failure) please use at least the following
configuration:
.. code-block:: bash
$ ../$LLVM_SRC_DIR/configure --with-abi=aapcs-vfp
#. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the
Pandaboard, have become hard-float platforms. The following set
of configuration options appears to be a good choice for this
platform:
.. code-block:: bash
./configure --build=armv7l-unknown-linux-gnueabihf \
--host=armv7l-unknown-linux-gnueabihf \
--target=armv7l-unknown-linux-gnueabihf --with-cpu=cortex-a9 \
--with-float=hard --with-abi=aapcs-vfp --with-fpu=neon \
--enable-targets=arm --enable-optimized --enable-assertions
#. ARM development boards can be unstable and you may experience that cores
are disappearing, caches being flushed on every big.LITTLE switch, and
other similar issues. To help ease the effect of this, set the Linux
scheduler to "performance" on **all** cores using this little script:
.. code-block:: bash
# The code below requires the package 'cpufrequtils' to be installed.
for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do
sudo cpufreq-set -c $cpu -g performance
done
#. Running the build on SD cards is ok, but they are more prone to failures
than good quality USB sticks, and those are more prone to failures than
external hard-drives (those are also a lot faster). So, at least, you
should consider to buy a fast USB stick. On systems with a fast eMMC,
that's a good option too.
#. Make sure you have a decent power supply (dozens of dollars worth) that can
provide *at least* 4 amperes, this is especially important if you use USB
devices with your board.
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