What’s the fun of only running code on platforms you physically have? Portability is important, and Libav actively targets several platforms. It can be useful to be able to try out the code, even if the hardware is totally unavailable.
Here is how to run Libav’s tests under aarch64, on x86_64 hardware and Ubuntu 14.04. This guide is provided in the hopes that it saves someone else 20 hours or more: there is a lot of once-excellent information which has become misleading, because a lot of progress has been made in aarch64 support. I have tried three approachs – building with Linaro’s cross-compiler, building under QEMU user emulation, and building under QEMU system emulation, and cross-compiling. Building with a cross-compiler is the fastest option. Building under user emulation is about ten times slower. Building under system emulation is about a hundred times slower. There is actually a fourth option, using ARM Foundation Model, but I have not tried it. Running under QEMU user emulation is the only approach I managed to make entirely work.
For all three approaches, you will want a rootfs; I used Ubuntu Core. You can download Ubuntu Core for aarch64 (a minimal rootfs; see https://wiki.ubuntu.com/Core to learn more), and untar it (as root) into a new directory. Then, set an environment variable that the rest of this guide/set of notes uses frequently, changing the path to match your system:
Approach 1 – build under QEMU’s user emulation.
Step 1) Set up QEMU. The days when using SUSE branches were necessary are over, but it still needs to be statically linked, and not all QEMU packages are. Ubuntu has a static QEMU:
sudo aptitude install qemu-user-static
This package also sets up binfmt for you. You can delete broken or stale binfmt information by running:
echo -1 > /proc/sys/fs/binfmt_misc/archnamehere – this can be useful, especially if you have previously installed QEMU by hand.
Step 2) Copy your QEMU binary into the chroot, as root, with:
cp `which qemu-aarch64-static` $a64root/usr/bin/
Step 3) As root, set up the aarch64 image so it can do DNS resolution, so you can freely use apt-get:
echo 'nameserver 22.214.171.124' > $a64root/etc/resolv.conf
Step 4) Chroot into your new system. Run
chroot $a64root /bin/bash as root.
At this point, you should be able to run an aarch64 version of
ls, and confirm with
file /bin/ls that it is an aarch64 binary.
Now you have a working, emulated, minimal aarch64 system.
On x86, you would run
aptitude build-dep libav, but there is no such package for aarch64 yet, so outside of the chroot, on the normal system, I installed apt-rdepends and ran:
apt-rdepends --build-depends --follow=DEPENDS libav
With version information stripped out, the following packages are considered dependencies:
debhelper frei0r-plugins-dev libasound2-dev libbz2-dev libcdio-cdda-dev libcdio-dev libcdio-paranoia-dev libdc1394-22-dev libfreetype6-dev libgnutls-dev libgsm1-dev libjack-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libopenjpeg-dev libopus-dev libpulse-dev libraw1394-dev librtmp-dev libschroedinger-dev libsdl1.2-dev libspeex-dev libtheora-dev libtiff-dev libtiff5-dev libva-dev libvdpau-dev libvo-aacenc-dev libvo-amrwbenc-dev libvorbis-dev libvpx-dev libx11-dev libx264-dev libxext-dev libxfixes-dev libxvidcore-dev libxvmc-dev texi2html yasm zlib1g-dev doxygen
Many of the libraries do not have current aarch64 Ubuntu packages, and neither does frei0r-plugins-dev, but running aptitude install on the above list installs a lot of useful things – including build-essential. The full list is in the command below; the missing packages are non-essential.
Step 5) Set it up:
apt-get install aptitude
aptitude install git debhelper frei0r-plugins-dev libasound2-dev libbz2-dev libcdio-cdda-dev libcdio-dev libcdio-paranoia-dev libdc1394-22-dev libfreetype6-dev libgnutls-dev libgsm1-dev libjack-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libopenjpeg-dev libopus-dev libpulse-dev libraw1394-dev librtmp-dev libschroedinger-dev libsdl1.2-dev libspeex-dev libtheora-dev libtiff-dev libtiff5-dev libva-dev libvdpau-dev libvo-aacenc-dev libvo-amrwbenc-dev libvorbis-dev libvpx-dev libx11-dev libx264-dev libxext-dev libxfixes-dev libxvidcore-dev libxvmc-dev texi2html yasm zlib1g-dev doxygen
Now it is time to actually build libav.
Step 6) Create a user within your chroot:
useradd -m auser, and switch to running as that user:
sudo -u auser bash, and type
cd to go to the home directory.
Step 7) Run
git clone git://git.libav.org/libav.git, then
./configure --disable-pthreads && make -j8 (change the 8 to approximately the number of CPU cores you have).
On my hardware, this takes 10-11 minutes, and ‘make fate’ takes about 16. Disabling pthreads is essential, as qemu-user does not handle threads well, and running the tests hangs randomly without it.
Approach 2: cross-compile (warning: I do not have the tests working with this approach).
1) Start by getting an aarch64 compiler. A good place to get one is http://releases.linaro.org/latest/components/toolchain/binaries/; I am using http://releases.linaro.org/latest/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2014.04_linux.tar.xz . Untar it, and add it to your path:
2) Make the cross-compiler work. Run
aptitude install lsb lib32stdc++6. Without this, invoking the compiler will say “No such file or directory”. See http://lists.linaro.org/pipermail/linaro-toolchain/2012-January/002016.html.
3) Under the libav directory (run
git clone git://git.libav.org/libav.git if you do not have one), type
mkdir a64crossbuild; cd a64crossbuild. Make sure the libav directory is somewhere under $a64root (it should simplify running the tests, later).
./configure --arch=aarch64 --cpu=generic --cross-prefix=aarch64-linux-gnu- --cc=aarch64-linux-gnu-gcc --target-os=linux --sysroot=$a64root --target-exec="qemu-aarch64-static -L $a64root" --disable-pthreads
This is a minimal variant of Jannau’s configuration – a developer who has recently done a lot of libav aarch64 work.
make -j8. On my hardware, it takes just under a minute.
make fate. Unfortunately, both versions of QEMU I tried hung on wait4 at this point (in fft-test, fate-fft-4), and used an extra couple of hundred megabytes of RAM per second until I stopped QEMU, even if I asked it to wait for a remote GDB. For anyone else trying this, https://lists.libav.org/pipermail/libav-devel/2014-May/059584.html has several useful tips for getting the tests to run after cross-compilation.
Approach 3: Use QEMU’s system emulation. In theory, this should allow you to use pthreads; in practice, the tests hung for me. The following May 9th post describes what to do: http://www.bennee.com/~alex/blog/2014/05/09/running-linux-in-qemus-aarch64-system-emulation-mode/. In short:
git clone git://git.qemu.org/qemu.git qemu.git && cd qemu.git && ./configure --target-list=aarch64-softmmu && make, then
./aarch64-softmmu/qemu-system-aarch64 -machine virt -cpu cortex-a57 -machine type=virt -nographic -smp 1 -m 2048 -kernel aarch64-linux-3.15rc2-buildroot.img --append "console=ttyAMA0" -fsdev local,id=r,path=$a64root,security_model=none -device virtio-9p-device,fsdev=r,mount_tag=r
Then, under the buildroot system, log in as root (no password), and type
mkdir /mnt/core && mount -t 9p -o trans=virtio r /mnt/core. At this point, you can run
chroot /mnt/core /bin/bash, and follow the approach 1 instructions from useradd onwards, except that ./configure without –disable-pthreads should theoretically work. On my system, ./configure takes a bit over 5 minutes with this approach. Running
make is quite slow;
time make took 113 minutes. Do not use -j – you are limited to a single core, so -j would slow compilation down slightly. However,
make fate consistently hung on acodec-pcm-alaw, and I have not yet figured out why.
Things not to do:
- Use a rootfs from a year ago; I am yet to try one that is not broken, and some come with fun bonuses like infinite file system loops. These cost me well over a dozen hours.
- Compile SUSE’s QEMU; qemu-system is bleeding-edge enough that you need to compile it from upstream, but SUSE’s patches have long been merged into the normal QEMU upstream. Unless you want qemu-system, you do not need to compile QEMU at all under Ubuntu 14.04.
- Leave the environment variables in this tutorial unset in a new shell and wonder why things do not work.