ndn-embedded

Cross-compiling NDN projects for home routers

=============================================

Contents

--------

*  [Introduction](#Introduction)

*  [Setting up the build host](#Setting-up-the-build-host)

*  [OpenWRT source and toolchain](#OpenWRT-source-and-toolchain)

*  [DD-WRT source and toolchain](#DD-WRT-source-and-toolchain)

*  [Compiling ndn-cxx](#Compiling-ndn-cxx)

*  [Using the ndn-cxx library with other NDN projects](#Using-the-ndn-cxx-library-with-other-NDN-projects)

*  [Concluding remarks](#Concluding-remarks)

Introduction

------------

This page describes how to cross compile NDN projects to run on wireless home routers that are supported by various open source firmwares, such as [OpenWRT](https://openwrt.org/) and [DD-WRT](http://dd-wrt.com/). Currently, it is easier to use OpenWRT. Building NDN projects to run on a router is a fairly straight forward process, but it is assumed that you are familiar with basic software development in a Linux environment, have some familiarity with cross compiling in general, and aren't afraid to get your hands dirty! There are also a couple considerations that need to be addressed when targeting smaller/embedded devices, especially concerning the limited flash storage typically available on routers.

The process of setting up the build host and actually compiling the NDN project will be the same regardless of the hardware/firmware you wish to target. Follow the corresponding section that matches your firmware to get the proper cross compile environment.

Setting up the build host

-------------------------

Steps in this guide were tested on a system running Debian 8 (jessie). Distribution specific commands, like installing packages, may have to be modified to suit your setup, but on the whole this guide should be applicable to any modern Linux system. All commands should be run as a normal user -- never as root!

Make sure you have the needed packages on the host system to compile the cross compile toolchain, libraries, and resulting firmware:

    sudo apt-get install build-essential subversion git-core libncurses5-dev zlib1g-dev gawk unzip pkg-config

Finally, before we actually begin the compilation process, be aware that the paths given below which reference a specific build target (like "mipsel\_mips32_uClibc-0.9.33.2") very well could be different for you. Be sure to make the appropriate adjustments to match your setup.

OpenWRT source and toolchain

----------------------------

Begin by fetching the current code for OpenWRT. Additional instructions are available on that project's wiki: [OpenWrt Buildroot - Installation](http://wiki.openwrt.org/doc/howto/buildroot.exigence). This guide assumes you checked out the source to your home directory.

    git clone git://git.openwrt.org/openwrt.git

    cd ~/openwrt/

You will need to edit the feed configuration file `feeds.conf.default` to re-enable the "oldpackages" repository so we can compile the `libcrypto++` library. Simply find that line, and remove the leading `#`. Once done, the line should look like `src-git oldpackages http://git.openwrt.org/packages.git`. Now, fetch the current feed information and populate the package choices for the next step.

    ./scripts/feeds update -a

    ./scripts/feeds install -a

We need to fetch the current feed information, as that is where we get the boost, libcrypto++, and libsqlite3 libraries to run in OpenWRT.

Now, run the configuration interface and adjust the settings as you need to match your device, etc.

    cd ~/openwrt/

    make menuconfig

**IMPORTANT** As of June 2015, the OpenWRT project has [switched to a new C library](https://lists.openwrt.org/pipermail/openwrt-devel/2015-June/033702.html) called musl. If you are running OpenWRT 15.05 (Chaos Calmer) or earlier, you must change the C library that the toolchain will use back to uClib, otherwise your cross compiled code _will not run_ on the router. If you are running a development version of OpenWRT compiled from code after June 16, 2015, it will use the musl C library and you do not have to change anything.

If you are running an old version of OpenWRT, follow these options in the menuconfig to change the C library. (Note that you will have to first enable the options before actually selecting them.)

    Advanced configuration options (for developers) --->

        Toolchain Options --->

            C Library implementation (use musl) --->

                Use uClib

Before compiling the firmware image, make sure the following libraries are selected so we can compile the NDN software. (Additional libraries might be required for projects that go beyond ndn-cxx, like `libpcap` for [NFD](http://redmine.named-data.net/projects/NFD).)

    Libraries --->

        database --->

            libsqlite3

        boost --->

            Select Boost Libraries --->

                Boost test package

                Boost atomic library

                Boost chrono library

                Boost date_time library

                Boost filesystem library

                Boost iostreams library

                Boost program_options library

                Boost random library

                Boost regex library

                Boost system library

                Boost thread library

        libcryptoxx

After you have the configuration to your liking, we need to compile the toolchain and libraries. This will take a while.

    make

Once the OpenWRT cross compile environment is compiled, we need to create two temporary symlinks so the later `./waf configure` stage will properly detect `libcrypto++`: (Again, remember that the target part of the path names may be different for you.)

    ln -s ~/openwrt/staging_dir/target-mipsel_mips32_uClibc-0.9.33.2/usr/include/crypto++ ~/openwrt/staging_dir/target-mipsel_mips32_uClibc-0.9.33.2/usr/include/cryptopp

    ln -s ~/openwrt/staging_dir/target-mipsel_mips32_uClibc-0.9.33.2/usr/lib/libcrypto++.so ~/openwrt/staging_dir/target-mipsel_mips32_uClibc-0.9.33.2/usr/lib/libcryptopp.so

Now the cross compile environment is ready for you to use. Proceed to [Compiling ndn-cxx](#Compiling-ndn-cxx).

DD-WRT source and toolchain

---------------------------

Configuring DD-WRT is a little more complicated than OpenWRT's setup. Begin by fetching the current code for DD-WRT. Additional instructions are available on that project's wiki: [Development - DD-WRT Wiki](http://www.dd-wrt.com/wiki/index.php/Development#Building_DD-WRT_from_Source). This guide assumes you checked out the source to your home directory.

    svn co svn://svn.dd-wrt.com/DD-WRT

    cd ~/DD-WRT/

Next, download the current cross compile toolchain for DD-WRT (note that the link on DD-WRT's wiki is broken, this is the correct one):

    wget ftp://ftp.dd-wrt.com/toolchains/toolchains.tar.gz

**FIXME** Need to complete this section. As of early 2015, it is easier to use the OpenWRT build system. I was able to cross-compile ndn-cxx and NFD using OpenWRT's system and then run the binaries on a DD-WRT flashed router. YMMV.

Now the cross compile environment is ready for you to use. Proceed to [Compiling ndn-cxx](#Compiling-ndn-cxx).

Compiling ndn-cxx

-----------------

In this section we will compile the [ndn-cxx](http://redmine.named-data.net/projects/ndn-cxx) library. Other NDN projects should compile in a similar manner.

As mentioned in the introduction, compiling for an embedded device can present issues not normally encountered. Chief among these for us is the very limited disk space to copy files to on the router. Normal compilation of a NDN project will by default produce binaries that include debug symbols. This can add an order of magnitude to the resulting binary size (101MB vs 15MB total), making it infeasible to run on a router. Therefore we will overwrite the default compiler flags with the `CXXFLAGS` variable. Additionally, the compilation process produces a statically linked library which is several megabytes in size. Unless it is specifically needed, there's no reason to copy it to the router where it will just waste space.

Begin by fetching the current release of ndn-cxx, 0.4.1 as of this writing:

    cd

    wget https://github.com/named-data/ndn-cxx/archive/ndn-cxx-0.4.1.tar.gz

    tar xf ndn-cxx-0.4.1.tar.gz

    cd ndn-cxx-ndn-cxx-0.4.1/

Now, set the needed environment variables so the configuration and compilation process use the cross compile environment we have setup.

**FIXME** this is currently specific to OpenWRT

    export TOOLCHAIN_PATH=$HOME/openwrt/staging_dir/toolchain-mipsel_mips32_gcc-4.8-linaro_uClibc-0.9.33.2/bin

    export CROSSCOMPILE_PATH=$HOME/openwrt/staging_dir/target-mipsel_mips32_uClibc-0.9.33.2/usr

    export CXX=$TOOLCHAIN_PATH/mipsel-openwrt-linux-uclibc-g++

    export AR=$TOOLCHAIN_PATH/mipsel-openwrt-linux-uclibc-ar

    export CXXFLAGS="-O2"

    export CFLAGS="-I$CROSSCOMPILE_PATH/include"

    export LDFLAGS="-L$CROSSCOMPILE_PATH/lib -lz"

Finally, configure and build the library. We will install the resulting binaries and source files into a folder within our home directory so we don't accidentally contaminate our host system with non-native binaries. If you are using the OpenWRT buildchain, you will see warnings during compilation that the STAGING_DIR environment variable is not set. This is a harmless warning that can be ignored.

    ./waf configure --prefix=/usr --sysconfdir=/etc --with-cryptopp=$CROSSCOMPILE_PATH --with-sqlite3=$CROSSCOMPILE_PATH --boost-includes=$CROSSCOMPILE_PATH/include --boost-libs=$CROSSCOMPILE_PATH/lib

    ./waf

    DESTDIR=$HOME/ndn-cxx-crosscompile ./waf install

You can now find the cross compiled binaries in `~/ndn-cxx-crosscompile`.

Using the ndn-cxx library with other NDN projects

-------------------------------------------------

Well, now that you've got the library cross compiled, you'll likely want to use it! Because it is both cross compiled as well as installed locally in your home directory, whatever project wants to use it will have to be told where to look. As a simple example, this section will show cross compiling [NFD](http://redmine.named-data.net/projects/NFD).

NFD requires the `libpcap` library, so make sure you've selected it when compiling your firmware and cross compile environment. (If you haven't, go back and do so, then rerun `make`. The second time should be much faster, as only the parts affected by configuration changes will have to be compiled.)

Similar to ndn-cxx, we will get the current release of NFD, 0.4.1 as of this writing:

    cd

    wget https://github.com/named-data/NFD/archive/NFD-0.4.1.tar.gz

    tar xf NFD-0.4.1.tar.gz

    cd NFD-NFD-0.4.1/

If the environment variables from the previous section aren't still set, reset them before proceeding.

NDN projects that use ndn-cxx assume they can get the necessary include directories and linking information via pkg-config. Because ndn-cxx isn't in the standard search path, we need to add it:

    export PKG_CONFIG_PATH=$HOME/ndn-cxx-crosscompile/usr/lib/pkgconfig:$PKG_CONFIG_PATH

Additionally, we need to tweak the configuration file for ndn-cxx so it includes the correct directories, since when the pkg-config file was generated, it assumed final installation based off the supplied `--prefix` option. Edit `~/ndn-cxx-crosscompile/usr/lib/pkgconfig/libndn-cxx.pc` and append the lib and include paths (the last arguments below) to the last two lines to (make sure to change the username part of the paths!):

    Libs: -L${libdir} [...snip...] -L/home/USER/ndn-cxx-crosscompile/usr/lib

    Cflags: -I${includedir} [...snip...] -I/home/USER/ndn-cxx-crosscompile/usr/include

Now, configure and compile NFD:

    ./waf configure --prefix=/usr --sysconfdir=/etc --with-libpcap=$CROSSCOMPILE_PATH --boost-includes=$CROSSCOMPILE_PATH/include --boost-libs=$CROSSCOMPILE_PATH/lib --without-websocket

    ./waf

    DESTDIR=$HOME/NFD-crosscompile ./waf install

Like before, the cross compiled binaries will be in `~/NFD-crosscompile`.

Concluding remarks

------------------

Hopefully this walk through has been helpful to you in your quest to cross compile a NDN project.

I have chosen not to talk about actually copying the resulting binaries to the router, as there are many ways to do so: package managers, tarballs, by hand, etc. There are plenty of better tutorials online that are easy to find if you need pointers doing this.