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Yocto Project Software Development Kit (SDK) Developer's Guide

Scott Rifenbark

Scotty's Documentation Services, LLC

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

For the latest version of this manual associated with this Yocto Project release, see the Yocto Project Software Development Kit (SDK) Developer's Guide from the Yocto Project website.
Revision History
Revision 2.1April 2016
Released with the Yocto Project 2.1 Release.
Revision 2.1.1August 2016
Released with the Yocto Project 2.1.1 Release.
Revision 2.1.2December 2016
Released with the Yocto Project 2.1.2 Release.

Table of Contents

1. Introduction
1.1. Introduction
1.1.1. The Cross-Development Toolchain
1.1.2. Sysroots
1.1.3. The QEMU Emulator
1.1.4. Eclipse Yocto Plug-in
1.1.5. User-Space Tools
1.2. SDK Development Model
2. Using the Standard SDK
2.1. Why use the Standard SDK and What is in It?
2.2. Installing the SDK
2.3. Running the SDK Environment Setup Script
2.4. Autotools-Based Projects
2.4.1. Creating and Running a Project Based on GNU Autotools
2.4.2. Passing Host Options
2.5. Makefile-Based Projects
2.6. Developing Applications Using Eclipse
2.6.1. Workflow Using Eclipse
2.6.2. Working Within Eclipse
3. Using the Extensible SDK
3.1. Setting Up to Use the Extensible SDK
3.2. Using devtool in Your SDK Workflow
3.2.1. Use devtool add to Add an Application
3.2.2. Use devtool modify to Modify the Source of an Existing Component
3.3. A Closer Look at devtool add
3.3.1. Name and Version
3.3.2. Dependency Detection and Mapping
3.3.3. License Detection
3.3.4. Adding Makefile-Only Software
3.3.5. Adding Native Tools
3.3.6. Adding Node.js Modules
3.4. Working With Recipes
3.4.1. Finding Logs and Work Files
3.4.2. Setting Configure Arguments
3.4.3. Sharing Files Between Recipes
3.4.4. Packaging
3.5. Restoring the Target Device to its Original State
3.6. Installing Additional Items Into the Extensible SDK
3.7. Updating the Extensible SDK
3.8. Creating a Derivative SDK With Additional Components
A. Obtaining the SDK
A.1. Locating Pre-Built SDK Installers
A.2. Building an SDK Installer
A.3. Extracting the Root Filesystem
A.4. Installed Standard SDK Directory Structure
A.5. Installed Extensible SDK Directory Structure
B. Customizing the SDK
B.1. Configuring the Extensible SDK
B.2. Adjusting the Extensible SDK to Suit Your Build System Setup
B.3. Changing the Appearance of the Extensible SDK
B.4. Providing Updates After Installing the Extensible SDK
B.5. Providing Additional Installable Extensible SDK Content
B.6. Minimizing the Size of the Extensible SDK Installer Download

Chapter 1. Introduction

1.1. Introduction

Welcome to the Yocto Project Software Development Kit (SDK) Developer's Guide. This manual provides information that explains how to use both the standard Yocto Project SDK and an extensible SDK to develop applications and images using the Yocto Project. Additionally, the manual also provides information on how to use the popular Eclipse™ IDE as part of your application development workflow within the SDK environment.

Prior to the 2.0 Release of the Yocto Project, application development was primarily accomplished through the use of the Application Development Toolkit (ADT) and the availability of stand-alone cross-development toolchains and other tools. With the 2.1 Release of the Yocto Project, application development has transitioned to within a more traditional SDK and extensible SDK.

A standard SDK consists of the following:

  • Cross-Development Toolchain: This toolchain contains a compiler, debugger, and various miscellaneous tools.

  • Libraries, Headers, and Symbols: The libraries, headers, and symbols are specific to the image (i.e. they match the image).

  • Environment Setup Script: This *.sh file, once run, sets up the cross-development environment by defining variables and preparing for SDK use.

You can use the standard SDK to independently develop and test code that is destined to run on some target machine.

An extensible SDK consists of everything that the standard SDK has plus tools that allow you to easily add new applications and libraries to an image, modify the source of an existing component, test changes on the target hardware, and easily integrate an application into the OpenEmbedded build system.

SDKs are completely self-contained. The binaries are linked against their own copy of libc, which results in no dependencies on the target system. To achieve this, the pointer to the dynamic loader is configured at install time since that path cannot be dynamically altered. This is the reason for a wrapper around the populate_sdk and populate_sdk_ext archives.

Another feature for the SDKs is that only one set of cross-compiler toolchain binaries are produced per architecture. This feature takes advantage of the fact that the target hardware can be passed to gcc as a set of compiler options. Those options are set up by the environment script and contained in variables such as CC and LD. This reduces the space needed for the tools. Understand, however, that a sysroot is still needed for every target since those binaries are target-specific.

The SDK development environment consists of the following:

  • The self-contained SDK, which is an architecture-specific cross-toolchain and matching sysroots (target and native) all built by the OpenEmbedded build system (e.g. the SDK). The toolchain and sysroots are based on a Metadata configuration and extensions, which allows you to cross-develop on the host machine for the target hardware.

  • The Quick EMUlator (QEMU), which lets you simulate target hardware. QEMU is not literally part of the SDK. You must build and include this emulator separately. However, QEMU plays an important role in the development process that revolves around use of the SDK.

  • The Eclipse IDE Yocto Plug-in. This plug-in is available for you if you are an Eclipse user. In the same manner as QEMU, the plug-in is not literally part of the SDK but is rather available for use as part of the development process.

  • Various user-space tools that greatly enhance your application development experience. These tools are also separate from the actual SDK but can be independently obtained and used in the development process.

1.1.1. The Cross-Development Toolchain

The Cross-Development Toolchain consists of a cross-compiler, cross-linker, and cross-debugger that are used to develop user-space applications for targeted hardware. This toolchain is created by running a toolchain installer script or through a Build Directory that is based on your Metadata configuration or extension for your targeted device. The cross-toolchain works with a matching target sysroot.

1.1.2. Sysroots

The native and target sysroots contain needed headers and libraries for generating binaries that run on the target architecture. The target sysroot is based on the target root filesystem image that is built by the OpenEmbedded build system and uses the same Metadata configuration used to build the cross-toolchain.

1.1.3. The QEMU Emulator

The QEMU emulator allows you to simulate your hardware while running your application or image. QEMU is not part of the SDK but is made available a number of ways:

  • If you have cloned the poky Git repository to create a Source Directory and you have sourced the environment setup script, QEMU is installed and automatically available.

  • If you have downloaded a Yocto Project release and unpacked it to create a Source Directory and you have sourced the environment setup script, QEMU is installed and automatically available.

  • If you have installed the cross-toolchain tarball and you have sourced the toolchain's setup environment script, QEMU is also installed and automatically available.

1.1.4. Eclipse Yocto Plug-in

The Eclipse IDE is a popular development environment and it fully supports development using the Yocto Project. When you install and configure the Eclipse Yocto Project Plug-in into the Eclipse IDE, you maximize your Yocto Project experience. Installing and configuring the Plug-in results in an environment that has extensions specifically designed to let you more easily develop software. These extensions allow for cross-compilation, deployment, and execution of your output into a QEMU emulation session. You can also perform cross-debugging and profiling. The environment also supports a suite of tools that allows you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

For information about the application development workflow that uses the Eclipse IDE and for a detailed example of how to install and configure the Eclipse Yocto Project Plug-in, see the "Developing Applications Using Eclipse" section.

1.1.5. User-Space Tools

User-space tools, which are available as part of the SDK development environment, can be helpful. The tools include LatencyTOP, PowerTOP, Perf, SystemTap, and Lttng-ust. These tools are common development tools for the Linux platform.

  • LatencyTOP: LatencyTOP focuses on latency that causes skips in audio, stutters in your desktop experience, or situations that overload your server even when you have plenty of CPU power left.

  • PowerTOP: Helps you determine what software is using the most power. You can find out more about PowerTOP at https://01.org/powertop/.

  • Perf: Performance counters for Linux used to keep track of certain types of hardware and software events. For more information on these types of counters see https://perf.wiki.kernel.org/. For examples on how to setup and use this tool, see the "perf" section in the Yocto Project Profiling and Tracing Manual.

  • SystemTap: A free software infrastructure that simplifies information gathering about a running Linux system. This information helps you diagnose performance or functional problems. SystemTap is not available as a user-space tool through the Eclipse IDE Yocto Plug-in. See http://sourceware.org/systemtap for more information on SystemTap. For examples on how to setup and use this tool, see the "SystemTap" section in the Yocto Project Profiling and Tracing Manual.

  • Lttng-ust: A User-space Tracer designed to provide detailed information on user-space activity. See http://lttng.org/ust for more information on Lttng-ust.

1.2. SDK Development Model

Fundamentally, the SDK fits into the development process as follows:

The SDK is installed on any machine and can be used to develop applications, images, and kernels. An SDK can even be used by a QA Engineer or Release Engineer. The fundamental concept is that the machine that has the SDK installed does not have to be associated with the machine that has the Yocto Project installed. A developer can independently compile and test an object on their machine and then, when the object is ready for integration into an image, they can simply make it available to the machine that has the Yocto Project. Once the object is available, the image can be rebuilt using the Yocto Project to produce the modified image.

You just need to follow these general steps:

  1. Install the SDK for your target hardware: For information on how to install the SDK, see the "Installing the SDK" section.

  2. Download the Target Image: The Yocto Project supports several target architectures and has many pre-built kernel images and root filesystem images.

    If you are going to develop your application on hardware, go to the machines download area and choose a target machine area from which to download the kernel image and root filesystem. This download area could have several files in it that support development using actual hardware. For example, the area might contain .hddimg files that combine the kernel image with the filesystem, boot loaders, and so forth. Be sure to get the files you need for your particular development process.

    If you are going to develop your application and then run and test it using the QEMU emulator, go to the machines/qemu download area. From this area, go down into the directory for your target architecture (e.g. qemux86_64 for an Intel®-based 64-bit architecture). Download kernel, root filesystem, and any other files you need for your process.

    Note

    To use the root filesystem in QEMU, you need to extract it. See the "Extracting the Root Filesystem" section for information on how to extract the root filesystem.

  3. Develop and Test your Application: At this point, you have the tools to develop your application. If you need to separately install and use the QEMU emulator, you can go to QEMU Home Page to download and learn about the emulator. See the "Using the Quick EMUlator (QEMU)" chapter in the Yocto Project Development Manual for information on using QEMU within the Yocto Project.

The remainder of this manual describes how to use both the standard SDK and the extensible SDK. Information also exists in appendix form that describes how you can build, install, and modify an SDK.

Chapter 2. Using the Standard SDK

This chapter describes the standard SDK and how to use it. Information covers the pieces of the SDK, how to install it, and presents several task-based procedures common for developing with a standard SDK.

Note

The tasks you can perform using a standard SDK are also applicable when you are using an extensible SDK. For information on the differences when using an extensible SDK as compared to a standard SDK, see the "Using the Extensible SDK" chapter.

2.1. Why use the Standard SDK and What is in It?

The Standard SDK provides a cross-development toolchain and libraries tailored to the contents of a specific image. You would use the Standard SDK if you want a more traditional toolchain experience.

The installed Standard SDK consists of several files and directories. Basically, it contains an SDK environment setup script, some configuration files, and host and target root filesystems to support usage. You can see the directory structure in the "Installed Standard SDK Directory Structure" section.

2.2. Installing the SDK

The first thing you need to do is install the SDK on your host development machine by running the *.sh installation script.

You can download a tarball installer, which includes the pre-built toolchain, the runqemu script, and support files from the appropriate directory under http://downloads.yoctoproject.org/releases/yocto/yocto-2.1.2/toolchain/. Toolchains are available for 32-bit and 64-bit x86 development systems from the i686 and x86_64 directories, respectively. The toolchains the Yocto Project provides are based off the core-image-sato image and contain libraries appropriate for developing against that image. Each type of development system supports five or more target architectures.

The names of the tarball installer scripts are such that a string representing the host system appears first in the filename and then is immediately followed by a string representing the target architecture.

     poky-glibc-host_system-image_type-arch-toolchain-release_version.sh

     Where:
         host_system is a string representing your development system:

                    i686 or x86_64.

         image_type is the image for which the SDK was built.

         arch is a string representing the tuned target architecture:

                    i586, x86_64, powerpc, mips, armv7a or armv5te

         release_version is a string representing the release number of the
                Yocto Project:

                    2.1.2, 2.1.2+snapshot
        

For example, the following toolchain installer is for a 64-bit development host system and a i586-tuned target architecture based off the SDK for core-image-sato and using the current 2.1.2 snapshot:

     poky-glibc-x86_64-core-image-sato-i586-toolchain-2.1.2.sh
        

The SDK and toolchains are self-contained and by default are installed into /opt/poky. However, when you run the SDK installer, you can choose an installation directory.

Note

You must change the permissions on the toolchain installer script so that it is executable:
     $ chmod +x poky-glibc-x86_64-core-image-sato-i586-toolchain-2.1.sh
            

The following command shows how to run the installer given a toolchain tarball for a 64-bit x86 development host system and a 32-bit x86 target architecture. The example assumes the toolchain installer is located in ~/Downloads/.

Note

If you do not have write permissions for the directory into which you are installing the SDK, the installer notifies you and exits. Be sure you have write permissions in the directory and run the installer again.

     $ ./poky-glibc-x86_64-core-image-sato-i586-toolchain-2.1.sh
     Poky (Yocto Project Reference Distro) SDK installer version 2.0
     ===============================================================
     Enter target directory for SDK (default: /opt/poky/2.1):
     You are about to install the SDK to "/opt/poky/2.1". Proceed[Y/n]? Y
     Extracting SDK.......................................................................done
     Setting it up...done
     SDK has been successfully set up and is ready to be used.
     Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
      $ . /opt/poky/2.1/environment-setup-i586-poky-linux
        

Again, reference the "Installed Standard SDK Directory Structure" section for more details on the resulting directory structure of the installed SDK.

2.3. Running the SDK Environment Setup Script

Once you have the SDK installed, you must run the SDK environment setup script before you can actually use it. This setup script resides in the directory you chose when you installed the SDK. For information on where this setup script can reside, see the "Obtaining the SDK" Appendix.

Before running the script, be sure it is the one that matches the architecture for which you are developing. Environment setup scripts begin with the string "environment-setup" and include as part of their name the tuned target architecture. For example, the command to source a setup script for an IA-based target machine using i586 tuning and located in the default SDK installation directory is as follows:

     $ source /opt/poky/2.1.2/environment-setup-i586-poky-linux
        

When you run the setup script, many environment variables are defined:

     SDKTARGETSYSROOT - The path to the sysroot used for cross-compilation
     PKG_CONFIG_PATH - The path to the target pkg-config files
     CONFIG_SITE - A GNU autoconf site file preconfigured for the target
     CC - The minimal command and arguments to run the C compiler
     CXX - The minimal command and arguments to run the C++ compiler
     CPP - The minimal command and arguments to run the C preprocessor
     AS - The minimal command and arguments to run the assembler
     LD - The minimal command and arguments to run the linker
     GDB - The minimal command and arguments to run the GNU Debugger
     STRIP - The minimal command and arguments to run 'strip', which strips symbols
     RANLIB - The minimal command and arguments to run 'ranlib'
     OBJCOPY - The minimal command and arguments to run 'objcopy'
     OBJDUMP - The minimal command and arguments to run 'objdump'
     AR - The minimal command and arguments to run 'ar'
     NM - The minimal command and arguments to run 'nm'
     TARGET_PREFIX - The toolchain binary prefix for the target tools
     CROSS_COMPILE - The toolchain binary prefix for the target tools
     CONFIGURE_FLAGS - The minimal arguments for GNU configure
     CFLAGS - Suggested C flags
     CXXFLAGS - Suggested C++ flags
     LDFLAGS - Suggested linker flags when you use CC to link
     CPPFLAGS - Suggested preprocessor flags
        

2.4. Autotools-Based Projects

Once you have a suitable cross-toolchain installed, it is very easy to develop a project outside of the OpenEmbedded build system. This section presents a simple "Helloworld" example that shows how to set up, compile, and run the project.

2.4.1. Creating and Running a Project Based on GNU Autotools

Follow these steps to create a simple Autotools-based project:

  1. Create your directory: Create a clean directory for your project and then make that directory your working location:

         $ mkdir $HOME/helloworld
         $ cd $HOME/helloworld
                        
  2. Populate the directory: Create hello.c, Makefile.am, and configure.ac files as follows:

    • For hello.c, include these lines:

           #include <stdio.h>
      
           main()
              {
                 printf("Hello World!\n");
              }
                                  
    • For Makefile.am, include these lines:

           bin_PROGRAMS = hello
           hello_SOURCES = hello.c
                                  
    • For configure.in, include these lines:

           AC_INIT(hello,0.1)
           AM_INIT_AUTOMAKE([foreign])
           AC_PROG_CC
           AC_PROG_INSTALL
           AC_OUTPUT(Makefile)
                                  
  3. Source the cross-toolchain environment setup file: Installation of the cross-toolchain creates a cross-toolchain environment setup script in the directory that the SDK was installed. Before you can use the tools to develop your project, you must source this setup script. The script begins with the string "environment-setup" and contains the machine architecture, which is followed by the string "poky-linux". Here is an example that sources a script from the default SDK installation directory that uses the 32-bit Intel x86 Architecture and the Krogoth Yocto Project release:

         $ source /opt/poky/2.1.2/environment-setup-i586-poky-linux
                        
  4. Generate the local aclocal.m4 files and create the configure script: The following GNU Autotools generate the local aclocal.m4 files and create the configure script:

         $ aclocal
         $ autoconf
                        
  5. Generate files needed by GNU coding standards: GNU coding standards require certain files in order for the project to be compliant. This command creates those files:

         $ touch NEWS README AUTHORS ChangeLog
                        
  6. Generate the configure file: This command generates the configure:

         $ automake -a
                        
  7. Cross-compile the project: This command compiles the project using the cross-compiler. The CONFIGURE_FLAGS environment variable provides the minimal arguments for GNU configure:

         $ ./configure ${CONFIGURE_FLAGS}
                        
  8. Make and install the project: These two commands generate and install the project into the destination directory:

         $ make
         $ make install DESTDIR=./tmp
                        
  9. Verify the installation: This command is a simple way to verify the installation of your project. Running the command prints the architecture on which the binary file can run. This architecture should be the same architecture that the installed cross-toolchain supports.

         $ file ./tmp/usr/local/bin/hello
                        
  10. Execute your project: To execute the project in the shell, simply enter the name. You could also copy the binary to the actual target hardware and run the project there as well:

         $ ./hello
                        

    As expected, the project displays the "Hello World!" message.

2.4.2. Passing Host Options

For an Autotools-based project, you can use the cross-toolchain by just passing the appropriate host option to configure.sh. The host option you use is derived from the name of the environment setup script found in the directory in which you installed the cross-toolchain. For example, the host option for an ARM-based target that uses the GNU EABI is armv5te-poky-linux-gnueabi. You will notice that the name of the script is environment-setup-armv5te-poky-linux-gnueabi. Thus, the following command works to update your project and rebuild it using the appropriate cross-toolchain tools:

     $ ./configure --host=armv5te-poky-linux-gnueabi \
        --with-libtool-sysroot=sysroot_dir
            

Note

If the configure script results in problems recognizing the --with-libtool-sysroot=sysroot-dir option, regenerate the script to enable the support by doing the following and then run the script again:
     $ libtoolize --automake
     $ aclocal -I ${OECORE_NATIVE_SYSROOT}/usr/share/aclocal \
        [-I dir_containing_your_project-specific_m4_macros]
     $ autoconf
     $ autoheader
     $ automake -a
                

2.5. Makefile-Based Projects

For Makefile-based projects, the cross-toolchain environment variables established by running the cross-toolchain environment setup script are subject to general make rules.

To illustrate this, consider the following four cross-toolchain environment variables:

     CC=i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.1.2/sysroots/i586-poky-linux
     LD=i586-poky-linux-ld --sysroot=/opt/poky/2.1.2/sysroots/i586-poky-linux
     CFLAGS=-O2 -pipe -g -feliminate-unused-debug-types
     CXXFLAGS=-O2 -pipe -g -feliminate-unused-debug-types
        

Now, consider the following three cases:

  • Case 1 - No Variables Set in the Makefile: Because these variables are not specifically set in the Makefile, the variables retain their values based on the environment.

  • Case 2 - Variables Set in the Makefile: Specifically setting variables in the Makefile during the build results in the environment settings of the variables being overwritten.

  • Case 3 - Variables Set when the Makefile is Executed from the Command Line: Executing the Makefile from the command line results in the variables being overwritten with command-line content regardless of what is being set in the Makefile. In this case, environment variables are not considered unless you use the "-e" flag during the build:

         $ make -e file
                    

    If you use this flag, then the environment values of the variables override any variables specifically set in the Makefile.

Note

For the list of variables set up by the cross-toolchain environment setup script, see the "Running the SDK Environment Setup Script" section.

2.6. Developing Applications Using Eclipse

If you are familiar with the popular Eclipse IDE, you can use an Eclipse Yocto Plug-in to allow you to develop, deploy, and test your application all from within Eclipse. This section describes general workflow using the SDK and Eclipse and how to configure and set up Eclipse.

2.6.1. Workflow Using Eclipse

The following figure and supporting list summarize the application development general workflow that employs both the SDK Eclipse.

  1. Prepare the host system for the Yocto Project: See "Supported Linux Distributions" and "Required Packages for the Host Development System" sections both in the Yocto Project Reference Manual for requirements. In particular, be sure your host system has the xterm package installed.

  2. Secure the Yocto Project kernel target image: You must have a target kernel image that has been built using the OpenEmbedded build system.

    Depending on whether the Yocto Project has a pre-built image that matches your target architecture and where you are going to run the image while you develop your application (QEMU or real hardware), the area from which you get the image differs.

    • Download the image from machines if your target architecture is supported and you are going to develop and test your application on actual hardware.

    • Download the image from machines/qemu if your target architecture is supported and you are going to develop and test your application using the QEMU emulator.

    • Build your image if you cannot find a pre-built image that matches your target architecture. If your target architecture is similar to a supported architecture, you can modify the kernel image before you build it. See the "Patching the Kernel" section in the Yocto Project Development manual for an example.

    For information on pre-built kernel image naming schemes for images that can run on the QEMU emulator, see the Yocto Project Software Development Kit (SDK) Developer's Guide.

  3. Install the SDK: The SDK provides a target-specific cross-development toolchain, the root filesystem, the QEMU emulator, and other tools that can help you develop your application. For information on how to install the SDK, see the "Installing the SDK" section.

  4. Secure the target root filesystem and the Cross-development toolchain: You need to find and download the appropriate root filesystem and the cross-development toolchain.

    You can find the tarballs for the root filesystem in the same area used for the kernel image. Depending on the type of image you are running, the root filesystem you need differs. For example, if you are developing an application that runs on an image that supports Sato, you need to get a root filesystem that supports Sato.

    You can find the cross-development toolchains at toolchains. Be sure to get the correct toolchain for your development host and your target architecture. See the "Locating Pre-Built SDK Installers" section for information and the "Installing the SDK" section for installation information.

  5. Create and build your application: At this point, you need to have source files for your application. Once you have the files, you can use the Eclipse IDE to import them and build the project. If you are not using Eclipse, you need to use the cross-development tools you have installed to create the image.

  6. Deploy the image with the application: If you are using the Eclipse IDE, you can deploy your image to the hardware or to QEMU through the project's preferences. If you are not using the Eclipse IDE, then you need to deploy the application to the hardware using other methods. Or, if you are using QEMU, you need to use that tool and load your image in for testing. See the "Using the Quick EMUlator (QEMU)" chapter in the Yocto Project Development Manual for information on using QEMU.

  7. Test and debug the application: Once your application is deployed, you need to test it. Within the Eclipse IDE, you can use the debugging environment along with the set of installed user-space tools to debug your application. Of course, the same user-space tools are available separately if you choose not to use the Eclipse IDE.

2.6.2. Working Within Eclipse

The Eclipse IDE is a popular development environment and it fully supports development using the Yocto Project.

Note

This release of the Yocto Project supports both the Luna and Kepler versions of the Eclipse IDE. Thus, the following information provides setup information for both versions.

When you install and configure the Eclipse Yocto Project Plug-in into the Eclipse IDE, you maximize your Yocto Project experience. Installing and configuring the Plug-in results in an environment that has extensions specifically designed to let you more easily develop software. These extensions allow for cross-compilation, deployment, and execution of your output into a QEMU emulation session as well as actual target hardware. You can also perform cross-debugging and profiling. The environment also supports a suite of tools that allows you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

This section describes how to install and configure the Eclipse IDE Yocto Plug-in and how to use it to develop your application.

2.6.2.1. Setting Up the Eclipse IDE

To develop within the Eclipse IDE, you need to do the following:

  1. Install the optimal version of the Eclipse IDE.

  2. Configure the Eclipse IDE.

  3. Install the Eclipse Yocto Plug-in.

  4. Configure the Eclipse Yocto Plug-in.

Note

Do not install Eclipse from your distribution's package repository. Be sure to install Eclipse from the official Eclipse download site as directed in the next section.

2.6.2.1.1. Installing the Eclipse IDE

It is recommended that you have the Luna SR2 (4.4.2) version of the Eclipse IDE installed on your development system. However, if you currently have the Kepler 4.3.2 version installed and you do not want to upgrade the IDE, you can configure Kepler to work with the Yocto Project.

If you do not have the Luna SR2 (4.4.2) Eclipse IDE installed, you can find the tarball at http://www.eclipse.org/downloads. From that site, choose the appropriate download from the "Eclipse IDE for C/C++ Developers". This version contains the Eclipse Platform, the Java Development Tools (JDT), and the Plug-in Development Environment.

Once you have downloaded the tarball, extract it into a clean directory. For example, the following commands unpack and install the downloaded Eclipse IDE tarball into a clean directory using the default name eclipse:

     $ cd ~
     $ tar -xzvf ~/Downloads/eclipse-cpp-luna-SR2-linux-gtk-x86_64.tar.gz
                    

2.6.2.1.2. Configuring the Eclipse IDE

This section presents the steps needed to configure the Eclipse IDE.

Before installing and configuring the Eclipse Yocto Plug-in, you need to configure the Eclipse IDE. Follow these general steps:

  1. Start the Eclipse IDE.

  2. Make sure you are in your Workbench and select "Install New Software" from the "Help" pull-down menu.

  3. Select Luna - http://download.eclipse.org/releases/luna from the "Work with:" pull-down menu.

    Note

    For Kepler, select Kepler - http://download.eclipse.org/releases/kepler

  4. Expand the box next to "Linux Tools" and select the Linux Tools LTTng Tracer Control, Linux Tools LTTng Userspace Analysis, and LTTng Kernel Analysis boxes. If these selections do not appear in the list, that means the items are already installed.

    Note

    For Kepler, select LTTng - Linux Tracing Toolkit box.

  5. Expand the box next to "Mobile and Device Development" and select the following boxes. Again, if any of the following items are not available for selection, that means the items are already installed:

    • C/C++ Remote Launch (Requires RSE Remote System Explorer)

    • Remote System Explorer End-user Runtime

    • Remote System Explorer User Actions

    • Target Management Terminal (Core SDK)

    • TCF Remote System Explorer add-in

    • TCF Target Explorer

  6. Expand the box next to "Programming Languages" and select the C/C++ Autotools Support and C/C++ Development Tools boxes. For Luna, these items do not appear on the list as they are already installed.

  7. Complete the installation and restart the Eclipse IDE.

2.6.2.1.3. Installing or Accessing the Eclipse Yocto Plug-in

You can install the Eclipse Yocto Plug-in into the Eclipse IDE one of two ways: use the Yocto Project's Eclipse Update site to install the pre-built plug-in or build and install the plug-in from the latest source code.

2.6.2.1.3.1. Installing the Pre-built Plug-in from the Yocto Project Eclipse Update Site

To install the Eclipse Yocto Plug-in from the update site, follow these steps:

  1. Start up the Eclipse IDE.

  2. In Eclipse, select "Install New Software" from the "Help" menu.

  3. Click "Add..." in the "Work with:" area.

  4. Enter http://downloads.yoctoproject.org/releases/eclipse-plugin/2.1.2/luna in the URL field and provide a meaningful name in the "Name" field.

    Note

    If you are using Kepler, use http://downloads.yoctoproject.org/releases/eclipse-plugin/2.1.2/kepler in the URL field.
  5. Click "OK" to have the entry added to the "Work with:" drop-down list.

  6. Select the entry for the plug-in from the "Work with:" drop-down list.

  7. Check the boxes next to Yocto Project ADT Plug-in, Yocto Project Bitbake Commander Plug-in, and Yocto Project Documentation plug-in.

  8. Complete the remaining software installation steps and then restart the Eclipse IDE to finish the installation of the plug-in.

    Note

    You can click "OK" when prompted about installing software that contains unsigned content.

2.6.2.1.3.2. Installing the Plug-in Using the Latest Source Code

To install the Eclipse Yocto Plug-in from the latest source code, follow these steps:

  1. Be sure your development system is not using OpenJDK to build the plug-in by doing the following:

    1. Use the Oracle JDK. If you don't have that, go to http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html and download the latest appropriate Java SE Development Kit tarball for your development system and extract it into your home directory.

    2. In the shell you are going to do your work, export the location of the Oracle Java. The previous step creates a new folder for the extracted software. You need to use the following export command and provide the specific location:

           export PATH=~/extracted_jdk_location/bin:$PATH
                                              

  2. In the same shell, create a Git repository with:

         $ cd ~
         $ git clone git://git.yoctoproject.org/eclipse-poky
                                    

  3. Be sure to checkout the correct tag. For example, if you are using Luna, do the following:

         $ git checkout luna/yocto-2.1.2
                                    

    This puts you in a detached HEAD state, which is fine since you are only going to be building and not developing.

    Note

    If you are building kepler, checkout the kepler/yocto-2.1.2 branch.

  4. Change to the scripts directory within the Git repository:

         $ cd scripts
                                    

  5. Set up the local build environment by running the setup script:

         $ ./setup.sh
                                    

  6. When the script finishes execution, it prompts you with instructions on how to run the build.sh script, which is also in the scripts directory of the Git repository created earlier.

  7. Run the build.sh script as directed. Be sure to provide the tag name, documentation branch, and a release name. Here is an example that uses the luna/yocto-2.1.2 tag, the master documentation branch, and krogoth for the release name:

         $ ECLIPSE_HOME=/home/scottrif/eclipse-poky/scripts/eclipse ./build.sh luna/yocto-2.1.2 master krogoth 2>&1 | tee -a build.log
                                    

    After running the script, the file org.yocto.sdk-release-date-archive.zip is in the current directory.

  8. If necessary, start the Eclipse IDE and be sure you are in the Workbench.

  9. Select "Install New Software" from the "Help" pull-down menu.

  10. Click "Add".

  11. Provide anything you want in the "Name" field.

  12. Click "Archive" and browse to the ZIP file you built in step eight. This ZIP file should not be "unzipped", and must be the *archive.zip file created by running the build.sh script.

  13. Click the "OK" button.

  14. Check the boxes that appear in the installation window to install the Yocto Project ADT Plug-in, Yocto Project Bitbake Commander Plug-in, and the Yocto Project Documentation plug-in.

  15. Finish the installation by clicking through the appropriate buttons. You can click "OK" when prompted about installing software that contains unsigned content.

  16. Restart the Eclipse IDE if necessary.

At this point you should be able to configure the Eclipse Yocto Plug-in as described in the "Configuring the Eclipse Yocto Plug-in" section.

2.6.2.1.4. Configuring the Eclipse Yocto Plug-in

Configuring the Eclipse Yocto Plug-in involves setting the Cross Compiler options and the Target options. The configurations you choose become the default settings for all projects. You do have opportunities to change them later when you configure the project (see the following section).

To start, you need to do the following from within the Eclipse IDE:

  • Choose "Preferences" from the "Window" menu to display the Preferences Dialog.

  • Click "Yocto Project ADT" to display the configuration screen.

2.6.2.1.4.1. Configuring the Cross-Compiler Options

To configure the Cross Compiler Options, you must select the type of toolchain, point to the toolchain, specify the sysroot location, and select the target architecture.

  • Selecting the Toolchain Type: Choose between Standalone pre-built toolchain and Build system derived toolchain for Cross Compiler Options.

    • Standalone Pre-built Toolchain: Select this mode when you are using a stand-alone cross-toolchain. For example, suppose you are an application developer and do not need to build a target image. Instead, you just want to use an architecture-specific toolchain on an existing kernel and target root filesystem.

    • Build System Derived Toolchain: Select this mode if the cross-toolchain has been installed and built as part of the Build Directory. When you select Build system derived toolchain, you are using the toolchain bundled inside the Build Directory.

  • Point to the Toolchain: If you are using a stand-alone pre-built toolchain, you should be pointing to where it is installed. See the "Installing the SDK" section for information about how the SDK is installed.

    If you are using a system-derived toolchain, the path you provide for the Toolchain Root Location field is the Build Directory. See the "Building an SDK Installer" section.

  • Specify the Sysroot Location: This location is where the root filesystem for the target hardware resides.

    The location of the sysroot filesystem depends on where you separately extracted and installed the filesystem.

    For information on how to install the toolchain and on how to extract and install the sysroot filesystem, see the "Building an SDK Installer" section.

  • Select the Target Architecture: The target architecture is the type of hardware you are going to use or emulate. Use the pull-down Target Architecture menu to make your selection. The pull-down menu should have the supported architectures. If the architecture you need is not listed in the menu, you will need to build the image. See the "Building Images" section of the Yocto Project Quick Start for more information.

2.6.2.1.4.2. Configuring the Target Options

You can choose to emulate hardware using the QEMU emulator, or you can choose to run your image on actual hardware.

  • QEMU: Select this option if you will be using the QEMU emulator. If you are using the emulator, you also need to locate the kernel and specify any custom options.

    If you selected Build system derived toolchain, the target kernel you built will be located in the Build Directory in tmp/deploy/images/machine directory. If you selected Standalone pre-built toolchain, the pre-built image you downloaded is located in the directory you specified when you downloaded the image.

    Most custom options are for advanced QEMU users to further customize their QEMU instance. These options are specified between paired angled brackets. Some options must be specified outside the brackets. In particular, the options serial, nographic, and kvm must all be outside the brackets. Use the man qemu command to get help on all the options and their use. The following is an example:

        serial ‘<-m 256 -full-screen>’
                                    

    Regardless of the mode, Sysroot is already defined as part of the Cross-Compiler Options configuration in the Sysroot Location: field.

  • External HW: Select this option if you will be using actual hardware.

Click the "OK" to save your plug-in configurations.

2.6.2.2. Creating the Project

You can create two types of projects: Autotools-based, or Makefile-based. This section describes how to create Autotools-based projects from within the Eclipse IDE. For information on creating Makefile-based projects in a terminal window, see the "Makefile-Based Projects" section.

Note

Do not use special characters in project names (e.g. spaces, underscores, etc.). Doing so can cause configuration to fail.

To create a project based on a Yocto template and then display the source code, follow these steps:

  1. Select "Project" from the "File -> New" menu.

  2. Double click CC++.

  3. Double click C Project to create the project.

  4. Expand Yocto Project ADT Autotools Project.

  5. Select Hello World ANSI C Autotools Project. This is an Autotools-based project based on a Yocto template.

  6. Put a name in the Project name: field. Do not use hyphens as part of the name.

  7. Click "Next".

  8. Add information in the Author and Copyright notice fields.

  9. Be sure the License field is correct.

  10. Click "Finish".

  11. If the "open perspective" prompt appears, click "Yes" so that you in the C/C++ perspective.

  12. The left-hand navigation pane shows your project. You can display your source by double clicking the project's source file.

2.6.2.3. Configuring the Cross-Toolchains

The earlier section, "Configuring the Eclipse Yocto Plug-in", sets up the default project configurations. You can override these settings for a given project by following these steps:

  1. Select "Change Yocto Project Settings" from the "Project" menu. This selection brings up the Yocto Project Settings Dialog and allows you to make changes specific to an individual project.

    By default, the Cross Compiler Options and Target Options for a project are inherited from settings you provided using the Preferences Dialog as described earlier in the "Configuring the Eclipse Yocto Plug-in" section. The Yocto Project Settings Dialog allows you to override those default settings for a given project.

  2. Make your configurations for the project and click "OK".

  3. Right-click in the navigation pane and select "Reconfigure Project" from the pop-up menu. This selection reconfigures the project by running autogen.sh in the workspace for your project. The script also runs libtoolize, aclocal, autoconf, autoheader, automake --a, and ./configure. Click on the "Console" tab beneath your source code to see the results of reconfiguring your project.

2.6.2.4. Building the Project

To build the project select "Build Project" from the "Project" menu. The console should update and you can note the cross-compiler you are using.

Note

When building "Yocto Project ADT Autotools" projects, the Eclipse IDE might display error messages for Functions/Symbols/Types that cannot be "resolved", even when the related include file is listed at the project navigator and when the project is able to build. For these cases only, it is recommended to add a new linked folder to the appropriate sysroot. Use these steps to add the linked folder:
  1. Select the project.

  2. Select "Folder" from the File > New menu.

  3. In the "New Folder" Dialog, select "Link to alternate location (linked folder)".

  4. Click "Browse" to navigate to the include folder inside the same sysroot location selected in the Yocto Project configuration preferences.

  5. Click "OK".

  6. Click "Finish" to save the linked folder.

2.6.2.5. Starting QEMU in User-Space NFS Mode

To start the QEMU emulator from within Eclipse, follow these steps:

Note

See the "Using the Quick EMUlator (QEMU)" chapter in the Yocto Project Development Manual for more information on using QEMU.

  1. Expose and select "External Tools" from the "Run" menu. Your image should appear as a selectable menu item.

  2. Select your image from the menu to launch the emulator in a new window.

  3. If needed, enter your host root password in the shell window at the prompt. This sets up a Tap 0 connection needed for running in user-space NFS mode.

  4. Wait for QEMU to launch.

  5. Once QEMU launches, you can begin operating within that environment. One useful task at this point would be to determine the IP Address for the user-space NFS by using the ifconfig command.

2.6.2.6. Deploying and Debugging the Application

Once the QEMU emulator is running the image, you can deploy your application using the Eclipse IDE and then use the emulator to perform debugging. Follow these steps to deploy the application.

Note

Currently, Eclipse does not support SSH port forwarding. Consequently, if you need to run or debug a remote application using the host display, you must create a tunneling connection from outside Eclipse and keep that connection alive during your work. For example, in a new terminal, run the following:
     ssh -XY user_name@remote_host_ip
                    
After running the command, add the command to be executed in Eclipse's run configuration before the application as follows:
     export DISPLAY=:10.0
                    

  1. Select "Debug Configurations..." from the "Run" menu.

  2. In the left area, expand C/C++Remote Application.

  3. Locate your project and select it to bring up a new tabbed view in the Debug Configurations Dialog.

  4. Enter the absolute path into which you want to deploy the application. Use the "Remote Absolute File Path for C/C++Application:" field. For example, enter /usr/bin/programname.

  5. Click on the "Debugger" tab to see the cross-tool debugger you are using.

  6. Click on the "Main" tab.

  7. Create a new connection to the QEMU instance by clicking on "new".

  8. Select TCF, which means Target Communication Framework.

  9. Click "Next".

  10. Clear out the "host name" field and enter the IP Address determined earlier.

  11. Click "Finish" to close the New Connections Dialog.

  12. Use the drop-down menu now in the "Connection" field and pick the IP Address you entered.

  13. Click "Debug" to bring up a login screen and login.

  14. Accept the debug perspective.

2.6.2.7. Running User-Space Tools

As mentioned earlier in the manual, several tools exist that enhance your development experience. These tools are aids in developing and debugging applications and images. You can run these user-space tools from within the Eclipse IDE through the "YoctoProjectTools" menu.

Once you pick a tool, you need to configure it for the remote target. Every tool needs to have the connection configured. You must select an existing TCF-based RSE connection to the remote target. If one does not exist, click "New" to create one.

Here are some specifics about the remote tools:

  • Lttng2.0 trace import: Selecting this tool transfers the remote target's Lttng tracing data back to the local host machine and uses the Lttng Eclipse plug-in to graphically display the output. For information on how to use Lttng to trace an application, see http://lttng.org/documentation and the "LTTng (Linux Trace Toolkit, next generation)" section, which is in the Yocto Project Profiling and Tracing Manual.

    Note

    Do not use Lttng-user space (legacy) tool. This tool no longer has any upstream support.

    Before you use the Lttng2.0 trace import tool, you need to setup the Lttng Eclipse plug-in and create a Tracing project. Do the following:

    1. Select "Open Perspective" from the "Window" menu and then select "Other..." to bring up a menu of other perspectives. Choose "Tracing".

    2. Click "OK" to change the Eclipse perspective into the Tracing perspective.

    3. Create a new Tracing project by selecting "Project" from the "File -> New" menu.

    4. Choose "Tracing Project" from the "Tracing" menu and click "Next".

    5. Provide a name for your tracing project and click "Finish".

    6. Generate your tracing data on the remote target.

    7. Select "Lttng2.0 trace import" from the "Yocto Project Tools" menu to start the data import process.

    8. Specify your remote connection name.

    9. For the Ust directory path, specify the location of your remote tracing data. Make sure the location ends with ust (e.g. /usr/mysession/ust).

    10. Click "OK" to complete the import process. The data is now in the local tracing project you created.

    11. Right click on the data and then use the menu to Select "Generic CTF Trace" from the "Trace Type... -> Common Trace Format" menu to map the tracing type.

    12. Right click the mouse and select "Open" to bring up the Eclipse Lttng Trace Viewer so you view the tracing data.

  • PowerTOP: Selecting this tool runs PowerTOP on the remote target machine and displays the results in a new view called PowerTOP.

    The "Time to gather data(sec):" field is the time passed in seconds before data is gathered from the remote target for analysis.

    The "show pids in wakeups list:" field corresponds to the -p argument passed to PowerTOP.

  • LatencyTOP and Perf: LatencyTOP identifies system latency, while Perf monitors the system's performance counter registers. Selecting either of these tools causes an RSE terminal view to appear from which you can run the tools. Both tools refresh the entire screen to display results while they run. For more information on setting up and using perf, see the "perf" section in the Yocto Project Profiling and Tracing Manual.

  • SystemTap: Systemtap is a tool that lets you create and reuse scripts to examine the activities of a live Linux system. You can easily extract, filter, and summarize data that helps you diagnose complex performance or functional problems. For more information on setting up and using SystemTap, see the SystemTap Documentation.

  • yocto-bsp: The yocto-bsp tool lets you quickly set up a Board Support Package (BSP) layer. The tool requires a Metadata location, build location, BSP name, BSP output location, and a kernel architecture. For more information on the yocto-bsp tool outside of Eclipse, see the "Creating a new BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

Chapter 3. Using the Extensible SDK

This chapter describes the extensible SDK and how to use it. The extensible SDK makes it easy to add new applications and libraries to an image, modify the source for an existing component, test changes on the target hardware, and ease integration into the rest of the OpenEmbedded build system.

Information in this chapter covers features that are not part of the standard SDK. In other words, the chapter presents information unique to the extensible SDK only. For information on how to use the standard SDK, see the "Using the Standard SDK" chapter.

3.1. Setting Up to Use the Extensible SDK

Getting set up to use the extensible SDK is identical to getting set up to use the standard SDK. You still need to locate and run the installer and then run the environment setup script. See the "Installing the SDK" and the "Running the SDK Environment Setup Script" sections for general information. The following items highlight the only differences between getting set up to use the extensible SDK as compared to the standard SDK:

  • Default Installation Directory: By default, the extensible SDK installs into the poky_sdk folder of your home directory. As with the standard SDK, you can choose to install the extensible SDK in any location when you run the installer. However, unlike the standard SDK, the location you choose needs to be writable for whichever users need to use the SDK, since files will need to be written under that directory during the normal course of operation.

  • Build Tools and Build System: The extensible SDK installer performs additional tasks as compared to the standard SDK installer. The extensible SDK installer extracts build tools specific to the SDK and the installer also prepares the internal build system within the SDK. Here is example output for running the extensible SDK installer:

         $ ./poky-glibc-x86_64-core-image-minimal-core2-64-toolchain-ext-2.1+snapshot.sh
         Poky (Yocto Project Reference Distro) Extensible SDK installer version 2.1+snapshot
         ===================================================================================
         Enter target directory for SDK (default: ~/poky_sdk):
         You are about to install the SDK to "/home/scottrif/poky_sdk". Proceed[Y/n]? Y
         Extracting SDK......................................................................done
         Setting it up...
         Extracting buildtools...
         Preparing build system...
         done
         SDK has been successfully set up and is ready to be used.
         Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
          $ . /home/scottrif/poky_sdk/environment-setup-core2-64-poky-linux
                    

After installing the SDK, you need to run the SDK environment setup script. Here is the output:

     $ source environment-setup-core2-64-poky-linux
     SDK environment now set up; additionally you may now run devtool to perform development tasks.
     Run devtool --help for further details.
        

Once you run the environment setup script, you have devtool available.

3.2. Using devtool in Your SDK Workflow

The cornerstone of the extensible SDK is a command-line tool called devtool. This tool provides a number of features that help you build, test and package software within the extensible SDK, and optionally integrate it into an image built by the OpenEmbedded build system.

The devtool command line is organized similarly to Git in that it has a number of sub-commands for each function. You can run devtool --help to see all the commands.

Two devtool subcommands that provide entry-points into development are:

  • devtool add: Assists in adding new software to be built.

  • devtool modify: Sets up an environment to enable you to modify the source of an existing component.

As with the OpenEmbedded build system, "recipes" represent software packages within devtool. When you use devtool add, a recipe is automatically created. When you use devtool modify, the specified existing recipe is used in order to determine where to get the source code and how to patch it. In both cases, an environment is set up so that when you build the recipe a source tree that is under your control is used in order to allow you to make changes to the source as desired. By default, both new recipes and the source go into a "workspace" directory under the SDK.

The remainder of this section presents the devtool add and devtool modify workflows.

3.2.1. Use devtool add to Add an Application

The devtool add command generates a new recipe based on existing source code. This command takes advantage of the workspace layer that many devtool commands use. The command is flexible enough to allow you to extract source code into both the workspace or a separate local Git repository and to use existing code that does not need to be extracted.

Depending on your particular scenario, the arguments and options you use with devtool add form different combinations. The following diagram shows common development flows you would use with the devtool add command:

  1. Generating the New Recipe: The top part of the flow shows three scenarios by which you could use devtool add to generate a recipe based on existing source code.

    In a shared development environment, it is typical where other developers are responsible for various areas of source code. As a developer, you are probably interested in using that source code as part of your development using the Yocto Project. All you need is access to the code, a recipe, and a controlled area in which to do your work.

    Within the diagram, three possible scenarios feed into the devtool add workflow:

    • Left: The left scenario represents a common situation where the source code does not exist locally and needs to be extracted. In this situation, you just let it get extracted to the default workspace - you do not want it in some specific location outside of the workspace. Thus, everything you need will be located in the workspace:

           $ devtool add recipe fetchuri
                                  

      With this command, devtool creates a recipe and an append file in the workspace as well as extracts the upstream source files into a local Git repository also within the sources folder.

    • Middle: The middle scenario also represents a situation where the source code does not exist locally. In this case, the code is again upstream and needs to be extracted to some local area - this time outside of the default workspace. As always, if required devtool creates a Git repository locally during the extraction. Furthermore, the first positional argument srctree in this case identifies where the devtool add command will locate the extracted code outside of the workspace:

           $ devtool add recipe srctree fetchuri
                                  

      In summary, the source code is pulled from fetchuri and extracted into the location defined by srctree as a local Git repository.

      Within workspace, devtool creates both the recipe and an append file for the recipe.

    • Right: The right scenario represents a situation where the source tree (srctree) has been previously prepared outside of the devtool workspace.

      The following command names the recipe and identifies where the existing source tree is located:

           $ devtool add recipe srctree
                                  

      The command examines the source code and creates a recipe for it placing the recipe into the workspace.

      Because the extracted source code already exists, devtool does not try to relocate it into the workspace - just the new the recipe is placed in the workspace.

      Aside from a recipe folder, the command also creates an append folder and places an initial *.bbappend within.

  2. Edit the Recipe: At this point, you can use devtool edit-recipe to open up the editor as defined by the $EDITOR environment variable and modify the file:

         $ devtool edit-recipe recipe
                        

    From within the editor, you can make modifications to the recipe that take affect when you build it later.

  3. Build the Recipe or Rebuild the Image: At this point in the flow, the next step you take depends on what you are going to do with the new code.

    If you need to take the build output and eventually move it to the target hardware, you would use devtool build:

         $ devtool build recipe
                        

    On the other hand, if you want an image to contain the recipe's packages for immediate deployment onto a device (e.g. for testing purposes), you can use the devtool build-image command:

         $ devtool build-image image
                        

  4. Deploy the Build Output: When you use the devtool build command to build out your recipe, you probably want to see if the resulting build output works as expected on target hardware.

    Note

    This step assumes you have a previously built image that is already either running in QEMU or running on actual hardware. Also, it is assumed that for deployment of the image to the target, SSH is installed in the image and if the image is running on real hardware that you have network access to and from your development machine.

    You can deploy your build output to that target hardware by using the devtool deploy-target command:

         $ devtool deploy-target recipe target
                        

    The target is a live target machine running as an SSH server.

    You can, of course, also deploy the image you build using the devtool build-image command to actual hardware. However, devtool does not provide a specific command that allows you to do this.

  5. Optionally Update the Recipe With Patch Files: Once you are satisfied with the recipe, if you have made any changes to the source tree that you want to have applied by the recipe, you need to generate patches from those changes. You do this before moving the recipe to its final layer and cleaning up the workspace area devtool uses. This optional step is especially relevant if you are using or adding third-party software.

    To convert commits created using Git to patch files, use the devtool update-recipe command.

    Note

    Any changes you want to turn into patches must be committed to the Git repository in the source tree.

         $ devtool update-recipe recipe
                        

  6. Move the Recipe to its Permanent Layer: Before cleaning up the workspace, you need to move the final recipe to its permanent layer. You must do this before using the devtool reset command if you want to retain the recipe.

  7. Reset the Recipe: As a final step, you can restore the state such that standard layers and the upstream source is used to build the recipe rather than data in the workspace. To reset the recipe, use the devtool reset command:

         $ devtool reset recipe
                        

3.2.2. Use devtool modify to Modify the Source of an Existing Component

The devtool modify command prepares the way to work on existing code that already has a recipe in place. The command is flexible enough to allow you to extract code, specify the existing recipe, and keep track of and gather any patch files from other developers that are associated with the code.

Depending on your particular scenario, the arguments and options you use with devtool modify form different combinations. The following diagram shows common development flows you would use with the devtool modify command:

  1. Preparing to Modify the Code: The top part of the flow shows three scenarios by which you could use devtool modify to prepare to work on source files. Each scenario assumes the following:

    • The recipe exists in some layer external to the devtool workspace.

    • The source files exist upstream in an un-extracted state or locally in a previously extracted state.

    The typical situation is where another developer has created some layer for use with the Yocto Project and their recipe already resides in that layer. Furthermore, their source code is readily available either upstream or locally.

    • Left: The left scenario represents a common situation where the source code does not exist locally and needs to be extracted. In this situation, the source is extracted into the default workspace location. The recipe, in this scenario, is in its own layer outside the workspace (i.e. meta-layername).

      The following command identifies the recipe and by default extracts the source files:

           $ devtool modify recipe
                                  

      Once devtoollocates the recipe, it uses the SRC_URI variable to locate the source code and any local patch files from other developers are located.

      Note

      You cannot provide an URL for srctree when using the devtool modify command.

      With this scenario, however, since no srctree argument exists, the devtool modify command by default extracts the source files to a Git structure. Furthermore, the location for the extracted source is the default area within the workspace. The result is that the command sets up both the source code and an append file within the workspace with the recipe remaining in its original location.

    • Middle: The middle scenario represents a situation where the source code also does not exist locally. In this case, the code is again upstream and needs to be extracted to some local area as a Git repository. The recipe, in this scenario, is again in its own layer outside the workspace.

      The following command tells devtool what recipe with which to work and, in this case, identifies a local area for the extracted source files that is outside of the default workspace:

           $ devtool modify recipe srctree
                                  

      As with all extractions, the command uses the recipe's SRC_URI to locate the source files. Once the files are located, the command by default extracts them. Providing the srctree argument instructs devtool where place the extracted source.

      Within workspace, devtool creates an append file for the recipe. The recipe remains in its original location but the source files are extracted to the location you provided with srctree.

    • Right: The right scenario represents a situation where the source tree (srctree) exists as a previously extracted Git structure outside of the devtool workspace. In this example, the recipe also exists elsewhere in its own layer.

      The following command tells devtool the recipe with which to work, uses the "-n" option to indicate source does not need to be extracted, and uses srctree to point to the previously extracted source files:

           $ devtool modify -n recipe srctree
                                  

      Once the command finishes, it creates only an append file for the recipe in the workspace. The recipe and the source code remain in their original locations.

  2. Edit the Source: Once you have used the devtool modify command, you are free to make changes to the source files. You can use any editor you like to make and save your source code modifications.

  3. Build the Recipe: Once you have updated the source files, you can build the recipe.

  4. Deploy the Build Output: When you use the devtool build command to build out your recipe, you probably want to see if the resulting build output works as expected on target hardware.

    Note

    This step assumes you have a previously built image that is already either running in QEMU or running on actual hardware. Also, it is assumed that for deployment of the image to the target, SSH is installed in the image and if the image is running on real hardware that you have network access to and from your development machine.

    You can deploy your build output to that target hardware by using the devtool deploy-target command:

         $ devtool deploy-target recipe target
                        

    The target is a live target machine running as an SSH server.

    You can, of course, also deploy the image you build using the devtool build-image command to actual hardware. However, devtool does not provide a specific command that allows you to do this.

  5. Optionally Create Patch Files for Your Changes: After you have debugged your changes, you can use devtool update-recipe to generate patch files for all the commits you have made.

    Note

    Patch files are generated only for changes you have committed.

         $ devtool update-recipe recipe
                        

    By default, the devtool update-recipe command creates the patch files in a folder named the same as the recipe beneath the folder in which the recipe resides, and updates the recipe's SRC_URI statement to point to the generated patch files.

    Note

    You can use the "--append LAYERDIR" option to cause the command to create append files in a specific layer rather than the default recipe layer.

  6. Restore the Workspace: The devtool reset restores the state so that standard layers and upstream sources are used to build the recipe rather than what is in the workspace.

         $ devtool reset recipe
                        

3.3. A Closer Look at devtool add

The devtool add command automatically creates a recipe based on the source tree with which you provide it. Currently, the command has support for the following:

  • Autotools (autoconf and automake)

  • CMake

  • Scons

  • qmake

  • Plain Makefile

  • Out-of-tree kernel module

  • Binary package (i.e. "-b" option)

  • Node.js module through npm

  • Python modules that use setuptools or distutils

Apart from binary packages, the determination of how a source tree should be treated is automatic based on the files present within that source tree. For example, if a CMakeLists.txt file is found, then the source tree is assumed to be using CMake and is treated accordingly.

Note

In most cases, you need to edit the automatically generated recipe in order to make it build properly. Typically, you would go through several edit and build cycles until you can build the recipe. Once the recipe can be built, you could use possible further iterations to test the recipe on the target device.

The remainder of this section covers specifics regarding how parts of the recipe are generated.

3.3.1. Name and Version

If you do not specify a name and version on the command line, devtool add attempts to determine the name and version of the software being built from various metadata within the source tree. Furthermore, the command sets the name of the created recipe file accordingly. If the name or version cannot be determined, the devtool add command prints an error and you must re-run the command with both the name and version or just the name or version specified.

Sometimes the name or version determined from the source tree might be incorrect. For such a case, you must reset the recipe:

     $ devtool reset -n recipename
            

After running the devtool reset command, you need to run devtool add again and provide the name or the version.

3.3.2. Dependency Detection and Mapping

The devtool add command attempts to detect build-time dependencies and map them to other recipes in the system. During this mapping, the command fills in the names of those recipes in the DEPENDS value within the recipe. If a dependency cannot be mapped, then a comment is placed in the recipe indicating such. The inability to map a dependency might be caused because the naming is not recognized or because the dependency simply is not available. For cases where the dependency is not available, you must use the devtool add command to add an additional recipe to satisfy the dependency and then come back to the first recipe and add its name to DEPENDS.

If you need to add runtime dependencies, you can do so by adding the following to your recipe:

     RDEPENDS_${PN} += "dependency1 dependency2 ..."
            

Note

The devtool add command often cannot distinguish between mandatory and optional dependencies. Consequently, some of the detected dependencies might in fact be optional. When in doubt, consult the documentation or the configure script for the software the recipe is building for further details. In some cases, you might find you can substitute the dependency for an option to disable the associated functionality passed to the configure script.

3.3.3. License Detection

The devtool add command attempts to determine if the software you are adding is able to be distributed under a common open-source license and sets the LICENSE value accordingly. You should double-check this value against the documentation or source files for the software you are building and update that LICENSE value if necessary.

The devtool add command also sets the LIC_FILES_CHKSUM value to point to all files that appear to be license-related. However, license statements often appear in comments at the top of source files or within documentation. Consequently, you might need to amend the LIC_FILES_CHKSUM variable to point to one or more of those comments if present. Setting LIC_FILES_CHKSUM is particularly important for third-party software. The mechanism attempts to ensure correct licensing should you upgrade the recipe to a newer upstream version in future. Any change in licensing is detected and you receive an error prompting you to check the license text again.

If the devtool add command cannot determine licensing information, the LICENSE value is set to "CLOSED" and the LIC_FILES_CHKSUM vaule remains unset. This behavior allows you to continue with development but is unlikely to be correct in all cases. Consequently, you should check the documentation or source files for the software you are building to determine the actual license.

3.3.4. Adding Makefile-Only Software

The use of make by itself is very common in both proprietary and open source software. Unfortunately, Makefiles are often not written with cross-compilation in mind. Thus, devtool add often cannot do very much to ensure that these Makefiles build correctly. It is very common, for example, to explicitly call gcc instead of using the CC variable. Usually, in a cross-compilation environment, gcc is the compiler for the build host and the cross-compiler is named something similar to arm-poky-linux-gnueabi-gcc and might require some arguments (e.g. to point to the associated sysroot for the target machine).

When writing a recipe for Makefile-only software, keep the following in mind:

  • You probably need to patch the Makefile to use variables instead of hardcoding tools within the toolchain such as gcc and g++.

  • The environment in which make runs is set up with various standard variables for compilation (e.g. CC, CXX, and so forth) in a similar manner to the environment set up by the SDK's environment setup script. One easy way to see these variables is to run the devtool build command on the recipe and then look in oe-logs/run.do_compile. Towards the top of this file you will see a list of environment variables that are being set. You can take advantage of these variables within the Makefile.

  • If the Makefile sets a default for a variable using "=", that default overrides the value set in the environment, which is usually not desirable. In this situation, you can either patch the Makefile so it sets the default using the "?=" operator, or you can alternatively force the value on the make command line. To force the value on the command line, add the variable setting to EXTRA_OEMAKE within the recipe as follows:

         EXTRA_OEMAKE += "'CC=${CC}' 'CXX=${CXX}'"
                        

    In the above example, single quotes are used around the variable settings as the values are likely to contain spaces because required default options are passed to the compiler.

  • Hardcoding paths inside Makefiles is often problematic in a cross-compilation environment. This is particularly true because those hardcoded paths often point to locations on the build host and thus will either be read-only or will introduce contamination into the cross-compilation by virtue of being specific to the build host rather than the target. Patching the Makefile to use prefix variables or other path variables is usually the way to handle this.

  • Sometimes a Makefile runs target-specific commands such as ldconfig. For such cases, you might be able to simply apply patches that remove these commands from the Makefile.

3.3.5. Adding Native Tools

Often, you need to build additional tools that run on the build host system as opposed to the target. You should indicate this using one of the following methods when you run devtool add:

  • Specify the name of the recipe such that it ends with "-native". Specifying the name like this produces a recipe that only builds for the build host.

  • Specify the "‐‐also-native" option with the devtool add command. Specifying this option creates a recipe file that still builds for the target but also creates a variant with a "-native" suffix that builds for the build host.

Note

If you need to add a tool that is shipped as part of a source tree that builds code for the target, you can typically accomplish this by building the native and target parts separately rather than within the same compilation process. Realize though that with the "‐‐also-native" option, you can add the tool using just one recipe file.

3.3.6. Adding Node.js Modules

You can use the devtool add command in the following form to add Node.js modules:

     $ devtool add "npm://registry.npmjs.org;name=forever;version=0.15.1"
            

The name and version parameters are mandatory. Lockdown and shrinkwrap files are generated and pointed to by the recipe in order to freeze the version that is fetched for the dependencies according to the first time. This also saves checksums that are verified on future fetches. Together, these behaviors ensure the reproducibility and integrity of the build.

Notes

  • You must use quotes around the URL. The devtool add does not require the quotes, but the shell considers ";" as a splitter between multiple commands. Thus, without the quotes, devtool add does not receive the other parts, which results in several "command not found" errors.

  • In order to support adding Node.js modules, a nodejs recipe must be part of your SDK in order to provide Node.js itself.

3.4. Working With Recipes

When building a recipe with devtool build the typical build progression is as follows:

  1. Fetch the source

  2. Unpack the source

  3. Configure the source

  4. Compiling the source

  5. Install the build output

  6. Package the installed output

For recipes in the workspace, fetching and unpacking is disabled as the source tree has already been prepared and is persistent. Each of these build steps is defined as a function, usually with a "do_" prefix. These functions are typically shell scripts but can instead be written in Python.

If you look at the contents of a recipe, you will see that the recipe does not include complete instructions for building the software. Instead, common functionality is encapsulated in classes inherited with the inherit directive, leaving the recipe to describe just the things that are specific to the software to be built. A base class exists that is implicitly inherited by all recipes and provides the functionality that most typical recipes need.

The remainder of this section presents information useful when working with recipes.

3.4.1. Finding Logs and Work Files

When you are debugging a recipe that you previously created using devtool add or whose source you are modifying by using the devtool modify command, after the first run of devtool build, you will find some symbolic links created within the source tree: oe-logs, which points to the directory in which log files and run scripts for each build step are created and oe-workdir, which points to the temporary work area for the recipe. You can use these links to get more information on what is happening at each build step.

These locations under oe-workdir are particularly useful:

  • image/: Contains all of the files installed at the do_install stage. Within a recipe, this directory is referred to by the expression ${D}.

  • sysroot-destdir/: Contains a subset of files installed within do_install that have been put into the shared sysroot. For more information, see the "Sharing Files Between Recipes" section.

  • packages-split/: Contains subdirectories for each package produced by the recipe. For more information, see the "Packaging" section.

3.4.2. Setting Configure Arguments

If the software your recipe is building uses GNU autoconf, then a fixed set of arguments is passed to it to enable cross-compilation plus any extras specified by EXTRA_OECONF set within the recipe. If you wish to pass additional options, add them to EXTRA_OECONF. Other supported build tools have similar variables (e.g. EXTRA_OECMAKE for CMake, EXTRA_OESCONS for Scons, and so forth). If you need to pass anything on the make command line, you can use EXTRA_OEMAKE to do so.

You can use the devtool configure-help command to help you set the arguments listed in the previous paragraph. The command determines the exact options being passed, and shows them to you along with any custom arguments specified through EXTRA_OECONF. If applicable, the command also shows you the output of the configure script's "‐‐help" option as a reference.

3.4.3. Sharing Files Between Recipes

Recipes often need to use files provided by other recipes on the build host. For example, an application linking to a common library needs access to the library itself and its associated headers. The way this access is accomplished within the extensible SDK is through the sysroot. One sysroot exists per "machine" for which the SDK is being built. In practical terms, this means a sysroot exists for the target machine, and a sysroot exists for the build host.

Recipes should never write files directly into the sysroot. Instead, files should be installed into standard locations during the do_install task within the ${D} directory. A subset of these files automatically go into the sysroot. The reason for this limitation is that almost all files that go into the sysroot are cataloged in manifests in order to ensure they can be removed later when a recipe is modified or removed. Thus, the sysroot is able to remain free from stale files.

3.4.4. Packaging

Packaging is not always particularly relevant within the extensible SDK. However, if you examine how build output gets into the final image on the target device, it is important to understand packaging because the contents of the image are expressed in terms of packages and not recipes.

During the do_package task, files installed during the do_install task are split into one main package, which is almost always named the same as the recipe, and several other packages. This separation is done because not all of those installed files are always useful in every image. For example, you probably do not need any of the documentation installed in a production image. Consequently, for each recipe the documentation files are separated into a -doc package. Recipes that package software that has optional modules or plugins might do additional package splitting as well.

After building a recipe you can see where files have gone by looking in the oe-workdir/packages-split directory, which contains a subdirectory for each package. Apart from some advanced cases, the PACKAGES and FILES variables controls splitting. The PACKAGES variable lists all of the packages to be produced, while the FILES variable specifies which files to include in each package, using an override to specify the package. For example, FILES_${PN} specifies the files to go into the main package (i.e. the main package is named the same as the recipe and ${PN} evaluates to the recipe name). The order of the PACKAGES value is significant. For each installed file, the first package whose FILES value matches the file is the package into which the file goes. Defaults exist for both the PACKAGES and FILES variables. Consequently, you might find you do not even need to set these variables in your recipe unless the software the recipe is building installs files into non-standard locations.

3.5. Restoring the Target Device to its Original State

If you use the devtool deploy-target command to write a recipe's build output to the target, and you are working on an existing component of the system, then you might find yourself in a situation where you need to restore the original files that existed prior to running the devtool deploy-target command. Because the devtool deploy-target command backs up any files it overwrites, you can use the devtool undeploy-target to restore those files and remove any other files the recipe deployed. Consider the following example:

     $ devtool undeploy-target lighttpd root@192.168.7.2
        

If you have deployed multiple applications, you can remove them all at once thus restoring the target device back to its original state:

     $ devtool undeploy-target -a root@192.168.7.2
        

Information about files deployed to the target as well as any backed up files are stored on the target itself. This storage of course requires some additional space on the target machine.

Note

The devtool deploy-target and devtool undeploy-target command do not currently interact with any package management system on the target device (e.g. RPM or OPKG). Consequently, you should not intermingle operations devtool deploy-target and the package manager operations on the target device. Doing so could result in a conflicting set of files.

3.6. Installing Additional Items Into the Extensible SDK

The extensible SDK typically only comes with a small number of tools and libraries out of the box. If you have a minimal SDK, then it starts mostly empty and is populated on-demand. However, sometimes you will need to explicitly install extra items into the SDK. If you need these extra items, you can first search for the items using the devtool search command. For example, suppose you need to link to libGL but you are not sure which recipe provides it. You can use the following command to find out:

     $ devtool search libGL
     mesa                  A free implementation of the OpenGL API
        

Once you know the recipe (i.e. mesa in this example), you can install it:

     $ devtool sdk-install mesa
        

By default, the devtool sdk-install assumes the item is available in pre-built form from your SDK provider. If the item is not available and it is acceptable to build the item from source, you can add the "-s" option as follows:

     $ devtool sdk-install -s mesa
        

It is important to remember that building the item from source takes significantly longer than installing the pre-built artifact. Also, if no recipe exists for the item you want to add to the SDK, you must instead add it using the devtool add command.

3.7. Updating the Extensible SDK

If you are working with an extensible SDK that gets occasionally updated (e.g. typically when that SDK has been provided to you by another party), then you will need to manually pull down those updates to your installed SDK.

To update your installed SDK, run the following:

     $ devtool sdk-update
         

The previous command assumes your SDK provider has set the default update URL for you. If that URL has not been set, you need to specify it yourself as follows:

     $ devtool sdk-update path_to_update_directory
         

Note

The URL needs to point specifically to a published SDK and not an SDK installer that you would download and install.

3.8. Creating a Derivative SDK With Additional Components

You might need to produce an SDK that contains your own custom libraries for sending to a third party (e.g., if you are a vendor with customers needing to build their own software for the target platform). If that is the case, then you can produce a derivative SDK based on the currently installed SDK fairly easily. Use these steps:

  1. If necessary, install an extensible SDK that you want to use as a base for your derivative SDK.

  2. Source the environment script for the SDK.

  3. Add the extra libraries or other components you want by using the devtool add command.

  4. Run the devtool build-sdk command.

The above procedure takes the recipes added to the workspace and constructs a new SDK installer containing those recipes and the resulting binary artifacts. The recipes go into their own separate layer in the constructed derivative SDK, leaving the workspace clean and ready for users to add their own recipes.

Appendix A. Obtaining the SDK

A.1. Locating Pre-Built SDK Installers

You can use existing, pre-built toolchains by locating and running an SDK installer script that ships with the Yocto Project. Using this method, you select and download an architecture-specific toolchain installer and then run the script to hand-install the toolchain.

You can find SDK installers here:

  • Standard SDK Installers Go to http://downloads.yoctoproject.org/releases/yocto/yocto-2.1.2/toolchain/ and find the folder that matches your host development system (i.e. i686 for 32-bit machines or x86_64 for 64-bit machines).

    Go into that folder and download the toolchain installer whose name includes the appropriate target architecture. The toolchains provided by the Yocto Project are based off of the core-image-sato image and contain libraries appropriate for developing against that image. For example, if your host development system is a 64-bit x86 system and you are going to use your cross-toolchain for a 32-bit x86 target, go into the x86_64 folder and download the following installer:

         poky-glibc-x86_64-core-image-sato-i586-toolchain-2.1.2.sh
                    

  • Extensible SDK Installers Installers for the extensible SDK are in http://downloads.yoctoproject.org/releases/yocto/yocto-2.1.2/toolchain/.

A.2. Building an SDK Installer

As an alternative to locating and downloading a toolchain installer, you can build the toolchain installer assuming you have first sourced the environment setup script. See the "Building Images" section in the Yocto Project Quick Start for steps that show you how to set up the Yocto Project environment. In particular, you need to be sure the MACHINE variable matches the architecture for which you are building and that the SDKMACHINE variable is correctly set if you are building a toolchain designed to run on an architecture that differs from your current development host machine (i.e. the build machine).

To build the toolchain installer for a standard SDK and populate the SDK image, use the following command:

     $ bitbake image -c populate_sdk
        

You can do the same for the extensible SDK using this command:

     $ bitbake image -c populate_sdk_ext
        

These commands result in a toolchain installer that contains the sysroot that matches your target root filesystem.

When the bitbake command completes, the toolchain installer will be in tmp/deploy/sdk in the Build Directory.

Note

By default, this toolchain does not build static binaries. If you want to use the toolchain to build these types of libraries, you need to be sure your image has the appropriate static development libraries. Use the IMAGE_INSTALL variable inside your local.conf file to install the appropriate library packages. Following is an example using glibc static development libraries:
     IMAGE_INSTALL_append = " glibc-staticdev"
            

A.3. Extracting the Root Filesystem

After installing the toolchain, for some use cases you might need to separately extract a root filesystem:

  • You want to boot the image using NFS.

  • You want to use the root filesystem as the target sysroot. For example, the Eclipse IDE environment with the Eclipse Yocto Plug-in installed allows you to use QEMU to boot under NFS.

  • You want to develop your target application using the root filesystem as the target sysroot.

To extract the root filesystem, first source the cross-development environment setup script to establish necessary environment variables. If you built the toolchain in the Build Directory, you will find the toolchain environment script in the tmp directory. If you installed the toolchain by hand, the environment setup script is located in /opt/poky/2.1.2.

After sourcing the environment script, use the runqemu-extract-sdk command and provide the filesystem image.

Following is an example. The second command sets up the environment. In this case, the setup script is located in the /opt/poky/2.1.2 directory. The third command extracts the root filesystem from a previously built filesystem that is located in the ~/Downloads directory. Furthermore, this command extracts the root filesystem into the qemux86-sato directory:

     $ cd ~
     $ source /opt/poky/2.1.2/environment-setup-i586-poky-linux
     $ runqemu-extract-sdk \
        ~/Downloads/core-image-sato-sdk-qemux86-2011091411831.rootfs.tar.bz2 \
        $HOME/qemux86-sato
        

You could now point to the target sysroot at qemux86-sato.

A.4. Installed Standard SDK Directory Structure

The following figure shows the resulting directory structure after you install the Standard SDK by running the *.sh SDK installation script:

The installed SDK consists of an environment setup script for the SDK, a configuration file for the target, a version file for the target, and the root filesystem (sysroots) needed to develop objects for the target system.

Within the figure, italicized text is used to indicate replaceable portions of the file or directory name. For example, install_dir/version is the directory where the SDK is installed. By default, this directory is /opt/poky/. And, version represents the specific snapshot of the SDK (e.g. 2.1.2+snapshot). Furthermore, target represents the target architecture (e.g. i586) and host represents the development system's architecture (e.g. x86_64). Thus, the complete names of the two directories within the sysroots could be i586-poky-linux and x86_64-pokysdk-linux for the target and host, respectively.

A.5. Installed Extensible SDK Directory Structure

The following figure shows the resulting directory structure after you install the Extensible SDK by running the *.sh SDK installation script:

The installed directory structure for the extensible SDK is quite different than the installed structure for the standard SDK. The extensible SDK does not separate host and target parts in the same manner as does the standard SDK. The extensible SDK uses an embedded copy of the OpenEmbedded build system, which has its own sysroots.

Of note in the directory structure are an environment setup script for the SDK, a configuration file for the target, a version file for the target, and a log file for the OpenEmbedded build system preparation script run by the installer.

Within the figure, italicized text is used to indicate replaceable portions of the file or directory name. For example, install_dir is the directory where the SDK is installed, which is poky_sdk by default. target represents the target architecture (e.g. i586) and host represents the development system's architecture (e.g. x86_64).

Appendix B. Customizing the SDK

This appendix presents customizations you can apply to both the standard and extensible SDK. Each subsection identifies the type of SDK to which the section applies.

B.1. Configuring the Extensible SDK

The extensible SDK primarily consists of a pre-configured copy of the OpenEmbedded build system from which it was produced. Thus, the SDK's configuration is derived using that build system and the following filters, which the OpenEmbedded build system applies against local.conf and auto.conf if they are present:

  • Variables whose values start with "/" are excluded since the assumption is that those values are paths that are likely to be specific to the build host.

  • Variables listed in SDK_LOCAL_CONF_BLACKLIST are excluded. The default value blacklists CONF_VERSION, BB_NUMBER_THREADS, PARALLEL_MAKE, PRSERV_HOST, and SSTATE_MIRRORS.

  • Variables listed in SDK_LOCAL_CONF_WHITELIST are included. Including a variable in the value of SDK_LOCAL_CONF_WHITELIST overrides either of the above two conditions. The default value is blank.

  • Classes inherited globally with INHERIT that are listed in SDK_INHERIT_BLACKLIST are disabled. Using SDK_INHERIT_BLACKLIST to disable these classes is is the typical method to disable classes that are problematic or unnecessary in the SDK context. The default value blacklists the buildhistory and icecc classes.

Additionally, the contents of conf/sdk-extra.conf, when present, are appended to the end of conf/local.conf within the produced SDK, without any filtering. The sdk-extra.conf file is particularly useful if you want to set a variable value just for the SDK and not the OpenEmbedded build system used to create the SDK.

B.2. Adjusting the Extensible SDK to Suit Your Build System Setup

In most cases, the extensible SDK defaults should work. However, some cases exist for which you might consider making adjustments:

  • If your SDK configuration inherits additional classes using the INHERIT variable and you do not need or want those classes enabled in the SDK, you can blacklist them by adding them to the SDK_INHERIT_BLACKLIST variable. The default value of SDK_INHERIT_BLACKLIST is set using the "?=" operator. Consequently, you will need to either set the complete value using "=" or append the value using "_append".

  • If you have classes or recipes that add additional tasks to the standard build flow (i.e. that execute as part of building the recipe as opposed to needing to be called explicitly), then you need to do one of the following:

    • Ensure the tasks are shared state tasks (i.e. their output is saved to and can be restored from the shared state cache), or that the tasks are able to be produced quickly from a task that is a shared state task and add the task name to the value of SDK_RECRDEP_TASKS.

    • Disable the tasks if they are added by a class and you do not need the functionality the class provides in the extensible SDK. To disable the tasks, add the class to SDK_INHERIT_BLACKLIST as previously described.

  • Generally, you want to have a shared state mirror set up so users of the SDK can add additional items to the SDK after installation without needing to build the items from source. See the "Providing Additional Installable Extensible SDK Content" section for information.

  • If you want users of the SDK to be able to easily update the SDK, you need to set the SDK_UPDATE_URL variable. For more information, see the "Providing Updates After Installing the Extensible SDK" section.

  • If you have adjusted the list of files and directories that appear in COREBASE (other than layers that are enabled through bblayers.conf), then you must list these files in COREBASE_FILES so that the files are copied into the SDK.

  • If your OpenEmbedded build system setup uses a different environment setup script other than oe-init-build-env or oe-init-build-env-memres, then you must set OE_INIT_ENV_SCRIPT to point to the environment setup script you use.

    Note

    You must also reflect this change in the value used for the COREBASE_FILES variable as previously described.

B.3. Changing the Appearance of the Extensible SDK

You can change the title shown by the SDK installer by setting the SDK_TITLE variable. By default, this title is derived from DISTRO_NAME when it is set. If the DISTRO_NAME variable is not set, the title is derived from the DISTRO variable.

B.4. Providing Updates After Installing the Extensible SDK

When you make changes to your configuration or to the metadata and if you want those changes to be reflected in installed SDKs, you need to perform additional steps to make it possible for those that use the SDK to update their installations with the devtool sdk-update command:

  1. Arrange to be created a directory that can be shared over HTTP or HTTPS.

  2. Set the SDK_UPDATE_URL variable to point to the corresponding HTTP or HTTPS URL. Setting this variable causes any SDK built to default to that URL and thus, the user does not have to pass the URL to the devtool sdk-update command.

  3. Build the extensible SDK normally (i.e., use the bitbake -c populate_sdk_ext imagename command).

  4. Publish the SDK using the following command:

         $ oe-publish-sdk some_path/sdk-installer.sh path_to_shared/http_directory
                    

    You must repeat this step each time you rebuild the SDK with changes that you want to make available through the update mechanism.

Completing the above steps allows users of the existing SDKs to simply run devtool sdk-update to retrieve the latest updates. See the "Updating the Extensible SDK" section for further information.

B.5. Providing Additional Installable Extensible SDK Content

If you want the users of the extensible SDK you are building to be able to add items to the SDK without needing to build the items from source, you need to do a number of things:

  1. Ensure the additional items you want the user to be able to install are actually built. You can ensure these items are built a number of different ways: 1) Build them explicitly, perhaps using one or more "meta" recipes that depend on lists of other recipes to keep things tidy, or 2) Build the "world" target and set EXCLUDE_FROM_WORLD_pn-recipename for the recipes you do not want built. See the EXCLUDE_FROM_WORLD variable for additional information.

  2. Expose the sstate-cache directory produced by the build. Typically, you expose this directory over HTTP or HTTPS.

  3. Set the appropriate configuration so that the produced SDK knows how to find the configuration. The variable you need to set is SSTATE_MIRRORS:

         SSTATE_MIRRORS = "file://.*  http://example.com/some_path/sstate-cache/PATH"
                    

    You can set the SSTATE_MIRRORS variable in two different places:

    • If the mirror value you are setting is appropriate to be set for both the OpenEmbedded build system that is actually building the SDK and the SDK itself (i.e. the mirror is accessible in both places or it will fail quickly on the OpenEmbedded build system side, and its contents will not interfere with the build), then you can set the variable in your local.conf or custom distro configuration file. You can then "whitelist" the variable through to the SDK by adding the following:

           SDK_LOCAL_CONF_WHITELIST = "SSTATE_MIRRORS"
                              

    • Alternatively, if you just want to set the SSTATE_MIRRORS variable's value for the SDK alone, create a conf/sdk-extra.conf either in your Build Directory or within any layer and put your SSTATE_MIRRORS setting within that file.

      Note

      This second option is the safest option should you have any doubts as to which method to use when setting SSTATE_MIRRORS.

B.6. Minimizing the Size of the Extensible SDK Installer Download

By default, the extensible SDK bundles the shared state artifacts for everything needed to reconstruct the image for which the SDK was built. This bundling can lead to an SDK installer file that is a Gigabyte or more in size. If the size of this file causes a problem, you can build an SDK that has just enough in it to install and provide access to the devtool command by setting the following in your configuration:

     SDK_EXT_TYPE = "minimal"
        

Setting SDK_EXT_TYPE to "minimal" produces an SDK installer that is around 35 Mbytes in size, which downloads and installs quickly. You need to realize, though, that the minimal installer does not install any libraries or tools out of the box. These must be installed either "on the fly" or through actions you perform using devtool or explicitly with the devtool sdk-install command.

In most cases, when building a minimal SDK you will need to also enable bringing in the information on a wider range of packages produced by the system. This is particularly true so that devtool add is able to effectively map dependencies it discovers in a source tree to the appropriate recipes. Also so that the devtool search command is able to return useful results.

To facilitate this wider range of information, you would additionally set the following:

     SDK_INCLUDE_PKGDATA = "1"
        

See the SDK_INCLUDE_PKGDATA variable for additional information.

Setting the SDK_INCLUDE_PKGDATA variable as shown causes the "world" target to be built so that information for all of the recipes included within it are available. Having these recipes available increases build time significantly and increases the size of the SDK installer by 30-80 Mbytes depending on how many recipes are included in your configuration.

You can use EXCLUDE_FROM_WORLD_pn-recipename for recipes you want to exclude. However, it is assumed that you would need to be building the "world" target if you want to provide additional items to the SDK. Consequently, building for "world" should not represent undue overhead in most cases.

Note

If you set SDK_EXT_TYPE to "minimal", then providing a shared state mirror is mandatory so that items can be installed as needed. See the "Providing Additional Installable Extensible SDK Content" section for more information.