Building and running embedded Linux .NET applications from first principles

Overview

This walk-through has the aim of taking you from a clean system through to including Mono in a build image using the meta-mono layer, then building and packaging an example .NET project for inclusion in that image.

You may already have Yocto installed and just be looking to work with Mono for the first time, in which case you can jump forward to the section you find most relevant,
such as building an example package on the host to test or adding the meta-mono layer to the Yocto build system.

The following assumptions are made. You are:

• familiar with basic Linux admin tasks
• aware of the Yocto Project Reference Manual here.
• using Ubuntu 14.04.4 LTS as your host build system
• working with Yocto 2.0 (Jethro) release

Obtain the required packages for your host system to support Yocto

First we will install the required host packages for Ubuntu as detailed in the quickstart, i.e.

 $ sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath socat libsdl1.2-dev xterm nano

Full details of system requirements and installation can be found in the Yocto Quickstart here

In addition, if you wish to build the example on the host, outside Yocto, you will need autoconf installed

 $ sudo apt-get install autoconf

Install Mono

Also install Mono on your host system as we'll use it to build and run some examples for test later

 $ sudo apt-get install mono-complete
 $ mono --version

With Ubuntu 14.04.4 LTS this will install Mono version 3.2.8 which is now quite old

If you wish to install a newer build of Mono to your host system you can follow the instructions here.

 $ sudo add-apt-repository ppa:directhex/monoxide
 $ sudo apt-get update
 $ sudo apt-get install mono-complete
 $ mono --version

Currently this will also install Mono 3.2.8 but may in future provide newer builds.

If you wish to use the absolute latest Mono then there are instructions you can follow to build a release tarball here and from git here. Be aware this may not be straightforward and that there can be issues, such as with missing files, if you follow this process.

Download and extract the Yocto 2.0 release

At the time of writing, the current release of Yocto (2.0) can be found here

 $ cd ~
 $ mkdir yocto
 $ cd yocto
 $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-2.0/poky-jethro-14.0.0.tar.bz2
 $ tar xjvf poky-jethro-14.0.0.tar.bz2

This will get you the Yocto 2.0 base meta-data and the bitbake tool. You can also add in extra layers, usually of the form "meta-foo" to provide machine support and additional functionality.

Configure the build environment to build an emulator image

 $ cd ~/yocto/poky-jethro-14.0.0
 $ source oe-init-build-env build_qemux86

This will create a build tree in "build_qemux86" although you could use a different name if you so wish with no adverse effects.

It is entirely possible to have many build trees in parallel in different folders and to switch between them using oe-init-build-env.

oe-init-build-env will create a default configuration file in conf/local/conf which will build an emulator image suitable for execution with qemu

Build a baseline image

After configuring the environment you will be left in the build_qemux86 folder.

You should then build a baseline image, which will take some time (numbers of hours)

 $ bitbake core-image-minimal

Build an example project on the host for testing (optional)

Building with autotools

The most straightforward way to compile non-.NET projects for different targets within Yocto is to make use of autotools

Projects which support autotools provide a set of template files which are then used by the autotools to generate Makefiles and associated configuration files which are appropriate to build for the target environment.

Similarly it is possible to compile Mono/.NET projects using autotools

A very basic example 'Hello World' style project called mono-helloworld has been committed to GitHub here

If you take a look at the two source files helloworld.cs and helloworldform.cs you can see the first outputs a 'Hello World' message to the console, and the second creates a Windows Form titled 'Hello World'.

Discussion of autotools template configuration for Mono is outside the scope of this guide, but the mono-helloworld project is based on the mono-skel example which can be found in the Autotools section of the Mono Application Deployment guidelines here

The project itself builds two .NET executables, helloworld and helloworldform respectively, the first of which is a console application and the second of which is a simple Windows Forms application.

To build the project on the host independently of Yocto first clone the example repository

 $ mkdir ~/host
 $ cd ~/host
 $ git clone https://github.com/DynamicDevices/mono-helloworld

Then run the autotools, configure the build, and make the project

 $ cd mono-helloworld
 $ ./autogen.sh
 $ ./configure --enable-winformdemo
 $ make

Following a successful compilation you will have a number of new files in the root of the build folder.

There are two new .NET executables src/helloworld.exe and src/helloworldform.exe.

You can run the first with

 $ mono src/helloworld.exe

It will output

HelloWorld

You can run the second with

 $ mono src/helloworldform.exe

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

 $ export DISPLAY=:0
 $ mono src/helloworldform.exe

This will give you a basic Windows Forms window title

So you have now shown that you can successfully fetch configure and build the project on the host.

Next we will look at how Yocto automates the this process of fetching, configuring and building, then also installs and packages the output files.

Building with xbuild

Many individuals develop with Visual Studio, Mono Develop, Xamarin Studio or other similar integrated development environments (IDEs).

Mono provides xbuild which is the Mono implementation of Microsoft's msbuild, discussed here.

In essence this enables a developer to create a solution of projects within their IDE of choice, then use xbuild to build within the Mono environment.

A useful workflow to follow may be to develop locally with an IDE of choice, commit to a git repository upon release, then use a Yocto recipe to build and package that release into an existing image, or for provision to a package feed for update to existing targets in the field.

The mono-helloworld project discussed above also provides a solution and project files to support build with xbuild, or indeed with an IDE such as Visual Studio.

If you have already built the examples using autotools remove the folder and start again.

 $ cd ~/host
 $ rm -Rf mono-helloworld

Check out the mono-helloworld project again

 $ git clone https://github.com/DynamicDevices/mono-helloworld

Run xbuild. (As you might guess from the name of the .sln file you could clone this example project to a Windows host and open it up with Visual Studio, and in fact that is how it was created)

 $ xbuild /p:Configuration=Debug mono-helloworld_vs2010.sln

This results in a number of new files, including two new Mono/.NET executables in bin/Debug helloworld.exe and helloworldform.exe

You can run the first with

 $ mono bin/Debug/helloworld.exe

It will output

HelloWorld

You can run the second with

 $ mono bin/Debug/helloworldform.exe

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

 $ export DISPLAY=:0
 $ mono bin/Debug/helloworldform.exe

This will give you a basic Windows Forms window title

So you have now shown that you can successfully fetch configure and build the project on the host.

Next we will look at how Yocto automates the this process of fetching, configuring and building, then also installs and packages the output files.

Adding the meta-mono layer to the Yocto build system

A preferred method for adding recipes to the build environment, and the method shown with this guide, is to place them within a new layer.

Layers isolate particular sets of build meta-data based on machine, functionality or similar, and help to keep the environment clean.

The meta-mono layer contains Mono specific recipes to support execution of .NET applications on target boards. The layer can be found here.

To use a new layer such as this you first clone the layer from its git repository and then add the layer to your bitbake configuration by editing conf/bblayers.conf

 $ cd ~/yocto/poky-daisy-11.0.0
 $ git clone git://git.yoctoproject.org/meta-mono
 $ cd ~/yocto/poky-daisy-11.0.0/build_qemux86
 $ nano conf/bblayers.conf

Your bblayers.conf should look similar to this

 # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
 # changes incompatibly
 LCONF_VERSION = "6"
 
 BBPATH = "${TOPDIR}"
 BBFILES ?= ""
 
 BBLAYERS ?= " \
   /home/user/yocto/poky-daisy-11.0.0/meta \
   /home/user/yocto/poky-daisy-11.0.0/meta-yocto \
   /home/user/yocto/poky-daisy-11.0.0/meta-yocto-bsp \
   "
 BBLAYERS_NON_REMOVABLE ?= " \
   /home/user/yocto/poky-daisy-11.0.0/meta \
   /home/user/yocto/poky-daisy-11.0.0/meta-yocto \
   "

Make the new layer visible to bitbake by adding a line to BBLAYERS

 BBLAYERS ?= " \
   /home/user/yocto/poky-daisy-11.0.0/meta \
   /home/user/yocto/poky-daisy-11.0.0/meta-yocto \
   /home/user/yocto/poky-daisy-11.0.0/meta-yocto-bsp \
   /home/user/yocto/poky-daisy-11.0.0/meta-mono \
   "

Now bitbake can see the recipes in the new layer.

You will also see when bitbake runs and shows the Build Configuration that the repository branch and hash of your layer is shown which is useful to know, particularly when comparing notes with others as to why a build fails, e.g.

 Build Configuration:
 BB_VERSION        = "1.22.0"
 BUILD_SYS         = "i686-linux"
 NATIVELSBSTRING   = "Ubuntu-12.04"
 TARGET_SYS        = "i586-poky-linux"
 MACHINE           = "qemux86"
 DISTRO            = "poky"
 DISTRO_VERSION    = "1.6"
 TUNE_FEATURES     = "m32 i586"
 TARGET_FPU        = ""
 meta
 meta-yocto
 meta-yocto-bsp    = "<unknown>:<unknown>"
 meta-mono         = "master:88c6d5f1961d58b3ec203ff19594f954c3e49cd9"

Build an image including Mono/.NET support

The meta-mono layer includes a recipe to build an image core-image-mono based on the Yocto standard image core-image-sato

To build this image

 $ bitbake core-image-mono

This may take a while, even if you have already built core-image-minimal as additional GUI support packages need to be built.

The core-image-mono recipe can be found here and pulls in an include file from here.

You can see in the include file that extra packages are added to the standard core-image-sato image.

 IMAGE_INSTALL += "mono mono-helloworld"
 

This is how you would add Mono support to your image within a recipe, or within a .bbappend file. In fact it should only be necessary to add the mono package as it is not necessary to have the examples unless you wish to for testing purposes.

The mono-helloworld recipe included here shows how to build the example project using autotools. For details see the recipe itself here, and more importantly the include file it pulls in here.

You could choose to replace mono-helloworld with mono-helloworld-xbuild which as the name suggests shows how to build the eaxmple project with xbuild.

Testing the .NET executable on an emulated target

Having built core-image-mono you can then run it up under qemu

To run up the image, simply use

$ runqemu qemux86

This will boot the emulator, load up the image, you'll see a kernel loading and then a basic user interface.

If you find that your keymap is incorrect you might wish to set this explicitly, for example

$ runqemu qemux86 qemuparams='-k en-gb'

or

$ runqemu qemux86 qemuparams='-k en-us'

Open up a terminal window using the appropriate icon, Log into the emulator as 'root', no password and run the examples.

You can run the first with

 $ mono helloworld.exe

Or alternatively the recipe installs a script to wrap use of Mono, so you can use the form

 $ helloworld

This will output

HelloWorld

You can run the second with

 $ mono /usr/lib/helloworldform.exe

or

 $ helloworldform

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

 $ export DISPLAY=:0
 $ mono /usr/lib/helloworld/helloworldform.exe

This will show a test Windows Forms form titled 'Hello World'

Lastly you can run a test GTK# application with

You can run the second with

 $ mono /usr/lib/helloworldgtk.exe

or

 $ helloworldgtk

Breakdown of an autotools recipe

This is the contents of the mono-helloworld_1.1.bb recipe here

require mono-helloworld.inc
SRC_URI[md5sum] = "79b0ba0044689789a54e3d55ec400fc0"
SRC_URI[sha256sum] = "56388435f29ce94007155acc39593c900b6d3248a7f281e83ed2101a6da455f0"

It can be seen that we provide a couple of checksums which relate to the release tarball that will be downloaded

Similarly the is the included mono-helloworld.inc file can be found here

 SUMMARY = "Mono Hello World"
 DESCRIPTION = "Test applications for Mono console and windows forms"
 AUTHOR = "Alex J Lennon <ajlennon@dynamicdevices.co.uk>"
 HOMEPAGE = "http://www.dynamicdevices.co.uk"
 SECTION = "mono/applications"
 PRIORITY = "optional"
 LICENSE = "GPLv3"
 LIC_FILES_CHKSUM = "file://LICENSE;md5=783b7e40cdfb4a1344d15b1f7081af66"
 DEPENDS = "mono"
 SRC_URI = "https://github.com/DynamicDevices/mono-helloworld/archive/v${PV}.tar.gz"
 inherit autotools
 FILES_${PN} = "${libdir}/helloworld/helloworld.exe \
 		${bindir}/helloworld \
        	${libdir}/helloworld/helloworldform.exe \
               ${bindir}/helloworldform \
 "

For more details on check-sums, licenses and so forth, see Building your own recipes from first principles and the Recipe & Style Patch Guide.

We have a dependency on the mono package, and again we inherit the autotools class to make use of the bitbake autotools functionality.

Lastly we override FILES_${PN} which controls the installed files which are added to the main output package. ${libdir} ${bindir} are standard GNU variable naming conventions for installation paths. For details see here and here.

In this case we have made sure that the helloworld executable goes to /usr/lib/helloworld/helloworld.exe as does the helloworldform.exe.

It might seem quite strange to be installing the executable assemblies to the /usr/lib location, but this is in line with Mono application deployment recommendations here.

We then install wrapper scripts to /usr/bin which can be called directly to run the respective examples. These scripts take the form

 #!/bin/sh
 exec @MONO@ @prefix@/lib/helloworld/@APP@.exe $MONO_EXTRA_ARGS "$@"

Breakdown of an xbuild recipe

The xbuild recipe is similar to the autotools recipe above, excepting that we override a couple of methods to ensure xbuild runs as we wish it too

This recipe can be found here.

First we include the definitions in the include file, and set the version specific checksums for the archive to be retrieved

require mono-helloworld.inc
SRC_URI[md5sum] = "79b0ba0044689789a54e3d55ec400fc0"
SRC_URI[sha256sum] = "56388435f29ce94007155acc39593c900b6d3248a7f281e83ed2101a6da455f0"

Then we set our source directory which must be correct for bitbake to find extracted files from the retrieved archive

REALPN = "mono-helloworld"
S = "${WORKDIR}/${REALPN}-${PV}"

Now we override the compilation method to call xbuild to build a particular .NET configuration against the a .SLN file in the archive

CONFIGURATION = "Debug"
do_compile() {
        xbuild /p:Configuration=${CONFIGURATION} ${REALPN}_vs2010.sln
}

Next we modify the installation method to make sure that the correct output files are installed and the executable scripts are modified to run the output assemblies

 do_install() {
         install -d "${D}${bindir}"
         install -d "${D}${libdir}/helloworld/.debug"
         install -m 0755 ${S}/bin/${CONFIGURATION}/*.mdb ${D}${libdir}/helloworld/.debug
         install -m 0755 ${S}/bin/${CONFIGURATION}/*.exe ${D}${libdir}/helloworld
 
         install -m 0755 ${S}/script.in ${D}${bindir}/helloworld
         sed -i "s|@MONO@|mono|g" ${D}${bindir}/helloworld
         sed -i "s|@prefix@|/usr|g" ${D}${bindir}/helloworld
         sed -i "s|@APP@|helloworld|g" ${D}${bindir}/helloworld
         install -m 0755 ${S}/script.in ${D}${bindir}/helloworldform
         sed -i "s|@MONO@|mono|g" ${D}${bindir}/helloworldform
         sed -i "s|@prefix@|/usr|g" ${D}${bindir}/helloworldform
         sed -i "s|@APP@|helloworld|g" ${D}${bindir}/helloworldform  
 }

Lastly we make sure that the .MDB debug files which are output are packaged correctly in the -dbg package. The other assemblies in ${libdir} and ${bindir} will be packaged correctly in the main output package by default

 FILES_${PN}-dbg += "${libdir}/helloworld/.debug/*"

For more details on check-sums, licenses and so forth, see Building your own recipes from first principles and the Recipe & Style Patch Guide.

Feedback

This is a living document. Please feel free to send comments, questions, corrections to Alex Lennon here