# Preparing for Application Development

In order to develop applications, you need set up your host development system. Several ways exist that allow you to install cross-development tools, QEMU, the Eclipse Yocto Plug-in, and other tools. This chapter describes how to prepare for application development.

## Installing the ADT and Toolchains

The following list describes installation methods that set up varying degrees of tool availability on your system. Regardless of the installation method you choose, you must `source` the cross-toolchain environment setup script, which establishes several key environment variables, before you use a toolchain. See the "Setting Up the Cross-Development Environment" section for more information.

Avoid mixing installation methods when installing toolchains for different architectures. For example, avoid using the ADT Installer to install some toolchains and then hand-installing cross-development toolchains by running the toolchain installer for different architectures. Mixing installation methods can result in situations where the ADT Installer becomes unreliable and might not install the toolchain.

If you must mix installation methods, you might avoid problems by deleting `/var/lib/opkg`, thus purging the `opkg` package metadata.

- Use the ADT installer script: This method is the recommended way to install the ADT because it automates much of the process for you. For example, you can configure the installation to install the QEMU emulator and the user-space NFS, specify which root filesystem profiles to download, and define the target sysroot location.

- Use an existing toolchain: Using this method, you select and download an architecture-specific toolchain installer and then run the script to hand-install the toolchain. If you use this method, you just get the cross-toolchain and QEMU - you do not get any of the other mentioned benefits had you run the ADT Installer script.

- Use the toolchain from within the Build Directory: If you already have a Build Directory, you can build the cross-toolchain within the directory. However, like the previous method mentioned, you only get the cross-toolchain and QEMU - you do not get any of the other benefits without taking separate steps.

### Using the ADT Installer

To run the ADT Installer, you need to get the ADT Installer tarball, be sure you have the necessary host development packages that support the ADT Installer, and then run the ADT Installer Script.

For a list of the host packages needed to support ADT installation and use, see the "ADT Installer Extras" lists in the "Required Packages for the Host Development System" section of the Yocto Project Reference Manual.

#### Getting the ADT Installer Tarball

The ADT Installer is contained in the ADT Installer tarball. You can get the tarball using either of these methods:

- Download the Tarball: You can download the tarball from into any directory.

- Build the Tarball: You can use BitBake to generate the tarball inside an existing Build Directory.

  If you use BitBake to generate the ADT Installer tarball, you must `source` the environment setup script (`&OE_INIT_FILE;` or `oe-init-build-env-memres`) located in the Source Directory before running the `bitbake` command that creates the tarball.

  The following example commands establish the Source Directory, check out the current release branch, set up the build environment while also creating the default Build Directory, and run the `bitbake` command that results in the tarball `poky/build/tmp/deploy/sdk/adt_installer.tar.bz2`:

  Before using BitBake to build the ADT tarball, be sure to make sure your `local.conf` file is properly configured. See the "User Configuration" section in the Yocto Project Reference Manual for general configuration information.

           $ cd ~
           $ git clone git://git.yoctoproject.org/poky
           $ cd poky
           $ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
           $ source &OE_INIT_FILE;
           $ bitbake adt-installer

#### Configuring and Running the ADT Installer Script

Before running the ADT Installer script, you need to unpack the tarball. You can unpack the tarball in any directory you wish. For example, this command copies the ADT Installer tarball from where it was built into the home directory and then unpacks the tarball into a top-level directory named `adt-installer`:

         $ cd ~
         $ cp poky/build/tmp/deploy/sdk/adt_installer.tar.bz2 $HOME
         $ tar -xjf adt_installer.tar.bz2

Unpacking it creates the directory `adt-installer`, which contains the ADT Installer script (`adt_installer`) and its configuration file (`adt_installer.conf`).

Before you run the script, however, you should examine the ADT Installer configuration file and be sure you are going to get what you want. Your configurations determine which kernel and filesystem image are downloaded.

The following list describes the configurations you can define for the ADT Installer. For configuration values and restrictions, see the comments in the `adt-installer.conf` file:

- `YOCTOADT_REPO`: This area includes the IPKG-based packages and the root filesystem upon which the installation is based. If you want to set up your own IPKG repository pointed to by `YOCTOADT_REPO`, you need to be sure that the directory structure follows the same layout as the reference directory set up at . Also, your repository needs to be accessible through HTTP.

- `YOCTOADT_TARGETS`: The machine target architectures for which you want to set up cross-development environments.

- `YOCTOADT_QEMU`: Indicates whether or not to install the emulator QEMU.

- `YOCTOADT_NFS_UTIL`: Indicates whether or not to install user-mode NFS. If you plan to use the Eclipse IDE Yocto plug-in against QEMU, you should install NFS.

  To boot QEMU images using our userspace NFS server, you need to be running `portmap` or `rpcbind`. If you are running `rpcbind`, you will also need to add the `-i` option when `rpcbind` starts up. Please make sure you understand the security implications of doing this. You might also have to modify your firewall settings to allow NFS booting to work.

- `YOCTOADT_ROOTFS_`arch: The root filesystem images you want to download from the `YOCTOADT_IPKG_REPO` repository.

- `YOCTOADT_TARGET_SYSROOT_IMAGE_`arch: The particular root filesystem used to extract and create the target sysroot. The value of this variable must have been specified with `YOCTOADT_ROOTFS_`arch. For example, if you downloaded both `minimal` and `sato-sdk` images by setting `YOCTOADT_ROOTFS_`arch to "minimal sato-sdk", then `YOCTOADT_ROOTFS_`arch must be set to either "minimal" or "sato-sdk".

- `YOCTOADT_TARGET_SYSROOT_LOC_`arch: The location on the development host where the target sysroot is created.

After you have configured the `adt_installer.conf` file, run the installer using the following command:

         $ cd adt-installer
         $ ./adt_installer

Once the installer begins to run, you are asked to enter the location for cross-toolchain installation. The default location is `/opt/poky/`release. After either accepting the default location or selecting your own location, you are prompted to run the installation script interactively or in silent mode. If you want to closely monitor the installation, choose “I” for interactive mode rather than “S” for silent mode. Follow the prompts from the script to complete the installation.

Once the installation completes, the ADT, which includes the cross-toolchain, is installed in the selected installation directory. You will notice environment setup files for the cross-toolchain in the installation directory, and image tarballs in the `adt-installer` directory according to your installer configurations, and the target sysroot located according to the `YOCTOADT_TARGET_SYSROOT_LOC_`arch variable also in your configuration file.

### Using a Cross-Toolchain Tarball

If you want to simply install a cross-toolchain by hand, you can do so by running the toolchain installer. The installer includes the pre-built cross-toolchain, the `runqemu` script, and support files. If you use this method to install the cross-toolchain, you might still need to install the target sysroot by installing and extracting it separately. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

Follow these steps:

1. Get your toolchain installer using one of the following methods:

   - Go to 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-&DISTRO;.sh

   - Build your own toolchain installer. For cases where you cannot use an installer from the download area, you can build your own as described in the "Optionally Building a Toolchain Installer" section.

2. Once you have the installer, run it to install the toolchain:

   You must change the permissions on the toolchain installer script so that it is executable.

   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/`.

            $ ~/Downloads/poky-glibc-x86_64-core-image-sato-i586-toolchain-&DISTRO;.sh

   The first thing the installer prompts you for is the directory into which you want to install the toolchain. The default directory used is `/opt/poky/&DISTRO;`. If you do not have write permissions for the directory into which you are installing the toolchain, the toolchain installer notifies you and exits. Be sure you have write permissions in the directory and run the installer again.

   When the script finishes, the cross-toolchain is installed. You will notice environment setup files for the cross-toolchain in the installation directory.

### Using BitBake and the Build Directory

A final way of making the cross-toolchain available is to use BitBake to generate the toolchain within an existing Build Directory. This method does not install the toolchain into the default `/opt` directory. As with the previous method, if you need to install the target sysroot, you must do that separately as well.

Follow these steps to generate the toolchain into the Build Directory:

1. Set up the Build Environment: Source the OpenEmbedded build environment setup script (i.e. `&OE_INIT_FILE;` or `oe-init-build-env-memres`) located in the Source Directory.

2. Check your Local Configuration File: At this point, you should be sure that the `MACHINE` variable in the `local.conf` file found in the `conf` directory of the Build Directory is set for the target architecture. Comments within the `local.conf` file list the values you can use for the `MACHINE` variable. If you do not change the `MACHINE` variable, the OpenEmbedded build system uses `qemux86` as the default target machine when building the cross-toolchain.

   You can populate the Build Directory with the cross-toolchains for more than a single architecture. You just need to edit the `MACHINE` variable in the `local.conf` file and re-run the `bitbake` command.

3. Make Sure Your Layers are Enabled: Examine the `conf/bblayers.conf` file and make sure that you have enabled all the compatible layers for your target machine. The OpenEmbedded build system needs to be aware of each layer you want included when building images and cross-toolchains. For information on how to enable a layer, see the "Enabling Your Layer" section in the Yocto Project Development Manual.

4. Generate the Cross-Toolchain: Run `bitbake meta-ide-support` to complete the cross-toolchain generation. Once the `bitbake` command finishes, the cross-toolchain is generated and populated within the Build Directory. You will notice environment setup files for the cross-toolchain that contain the string "`environment-setup`" in the Build Directory's `tmp` folder.

   Be aware that when you use this method to install the toolchain, you still need to separately extract and install the sysroot filesystem. For information on how to do this, see the "Extracting the Root Filesystem" section.

## Setting Up the Cross-Development Environment

Before you can develop using the cross-toolchain, you need to set up the cross-development environment by sourcing the toolchain's environment setup script. If you used the ADT Installer or hand-installed cross-toolchain, then you can find this script in the directory you chose for installation. For this release, the default installation directory is `&YOCTO_ADTPATH_DIR;`. If you installed the toolchain in the Build Directory, you can find the environment setup script for the toolchain in the Build Directory's `tmp` directory.

Be sure to run the environment setup script 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 architecture. For example, the toolchain environment setup script for a 64-bit IA-based architecture installed in the default installation directory would be the following:

         &YOCTO_ADTPATH_DIR;/environment-setup-x86_64-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

## Securing Kernel and Filesystem Images

You will need to have a kernel and filesystem image to boot using your hardware or the QEMU emulator. Furthermore, if you plan on booting your image using NFS or you want to use the root filesystem as the target sysroot, you need to extract the root filesystem.

### Getting the Images

To get the kernel and filesystem images, you either have to build them or download pre-built versions. For an example of how to build these images, see the "Buiding Images" section of the Yocto Project Quick Start. For an example of downloading pre-build versions, see the "Example Using Pre-Built Binaries and QEMU" section.

The Yocto Project ships basic kernel and filesystem images for several architectures (`x86`, `x86-64`, `mips`, `powerpc`, and `arm`) that you can use unaltered in the QEMU emulator. These kernel images reside in the release area - and are ideal for experimentation using Yocto Project. For information on the image types you can build using the OpenEmbedded build system, see the "Images" chapter in the Yocto Project Reference Manual.

If you are planning on developing against your image and you are not building or using one of the Yocto Project development images (e.g. `core-image-*-dev`), you must be sure to include the development packages as part of your image recipe.

If you plan on remotely deploying and debugging your application from within the Eclipse IDE, you must have an image that contains the Yocto Target Communication Framework (TCF) agent (`tcf-agent`). You can do this by including the `eclipse-debug` image feature.

See the "Image Features" section in the Yocto Project Reference Manual for information on image features.
To include the `eclipse-debug` image feature, modify your `local.conf` file in the Build Directory so that the `EXTRA_IMAGE_FEATURES` variable includes the "eclipse-debug" feature. After modifying the configuration file, you can rebuild the image. Once the image is rebuilt, the `tcf-agent` will be included in the image and is launched automatically after the boot.

### Extracting the Root Filesystem

If you install your toolchain by hand or build it using BitBake and you need a root filesystem, you need to extract it separately. If you use the ADT Installer to install the ADT, the root filesystem is automatically extracted and installed.

Here are some cases where you need to extract the 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/&DISTRO;`.

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/&DISTRO;` 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/&DISTRO;/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`.

## Optionally Building a Toolchain Installer

As an alternative to locating and downloading a toolchain installer, you can build the toolchain installer if you have a Build Directory.

Although not the preferred method, it is also possible to use `bitbake meta-toolchain` to build the toolchain installer. If you do use this method, you must separately install and extract the target sysroot. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

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

         $ bitbake image -c populate_sdk

The command results in a toolchain installer that contains the sysroot that matches your target root filesystem.

Another powerful feature is that the toolchain is 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` archive.

Another feature is that only one set of cross-canadian 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.

Remember, before using any BitBake command, you must source the build environment setup script (i.e. `&OE_INIT_FILE;` or `oe-init-build-env-memres`) located in the Source Directory and you must make sure your `conf/local.conf` variables are correct. 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).

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

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"

## Optionally Using an External Toolchain

You might want to use an external toolchain as part of your development. If this is the case, the fundamental steps you need to accomplish are as follows:

- Understand where the installed toolchain resides. For cases where you need to build the external toolchain, you would need to take separate steps to build and install the toolchain.

- Make sure you add the layer that contains the toolchain to your `bblayers.conf` file through the `BBLAYERS` variable.

- Set the `EXTERNAL_TOOLCHAIN` variable in your `local.conf` file to the location in which you installed the toolchain.

A good example of an external toolchain used with the Yocto Project is Mentor Graphics Sourcery G++ Toolchain. You can see information on how to use that particular layer in the `README` file at . You can find further information by reading about the `TCMODE` variable in the Yocto Project Reference Manual's variable glossary.

## Example Using Pre-Built Binaries and QEMU

If hardware, libraries and services are stable, you can get started by using a pre-built binary of the filesystem image, kernel, and toolchain and run it using the QEMU emulator. This scenario is useful for developing application software.

Using a Pre-Built Image

For this scenario, you need to do several things:

- Install the appropriate stand-alone toolchain tarball.

- Download the pre-built image that will boot with QEMU. You need to be sure to get the QEMU image that matches your target machine’s architecture (e.g. x86, ARM, etc.).

- Download the filesystem image for your target machine's architecture.

- Set up the environment to emulate the hardware and then start the QEMU emulator.

### Installing the Toolchain

You can download a tarball installer, which includes the pre-built toolchain, the `runqemu` script, and support files from the appropriate directory under . 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 a string representing the image you wish to
                    develop a Software Development Toolkit (SDK) for use against.
                    The Yocto Project builds toolchain installers using the
                    following BitBake command:

                        bitbake core-image-sato -c populate_sdk

             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:

                        &DISTRO;, &DISTRO;+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`:

         poky-glibc-x86_64-core-image-sato-i586-toolchain-&DISTRO;.sh

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

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. You must change the permissions on the toolchain installer script so that it is executable.

The example assumes the toolchain installer is located in `~/Downloads/`.

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

         $ ~/Downloads/poky-glibc-x86_64-core-image-sato-i586-toolchain-&DISTRO;.sh

For more information on how to install tarballs, see the "Using a Cross-Toolchain Tarball" and "Using BitBake and the Build Directory" sections in the Yocto Project Application Developer's Guide.

### Downloading the Pre-Built Linux Kernel

You can download the pre-built Linux kernel suitable for running in the QEMU emulator from . Be sure to use the kernel that matches the architecture you want to simulate. Download areas exist for the five supported machine architectures: `qemuarm`, `qemumips`, `qemuppc`, `qemux86`, and `qemux86-64`.

Most kernel files have one of the following forms:

         *zImage-qemuarch.bin
         vmlinux-qemuarch.bin

         Where:
             arch is a string representing the target architecture:
                    x86, x86-64, ppc, mips, or arm.

You can learn more about downloading a Yocto Project kernel in the "Yocto Project Kernel" bulleted item in the Yocto Project Development Manual.

### Downloading the Filesystem

You can also download the filesystem image suitable for your target architecture from . Again, be sure to use the filesystem that matches the architecture you want to simulate.

The filesystem image has two tarball forms: `ext3` and `tar`. You must use the `ext3` form when booting an image using the QEMU emulator. The `tar` form can be flattened out in your host development system and used for build purposes with the Yocto Project.

         core-image-profile-qemuarch.ext3
         core-image-profile-qemuarch.tar.bz2

         Where:
             profile is the filesystem image's profile:
                       lsb, lsb-dev, lsb-sdk, lsb-qt3, minimal, minimal-dev, sato,
                       sato-dev, or sato-sdk. For information on these types of image
                       profiles, see the "Images"
                       chapter in the Yocto Project Reference Manual.

             arch is a string representing the target architecture:
                    x86, x86-64, ppc, mips, or arm.

### Setting Up the Environment and Starting the QEMU Emulator

Before you start the QEMU emulator, you need to set up the emulation environment. The following command form sets up the emulation environment.

         $ source &YOCTO_ADTPATH_DIR;/environment-setup-arch-poky-linux-if

         Where:
             arch is a string representing the target architecture:
                    i586, x86_64, ppc603e, mips, or armv5te.

             if is a string representing an embedded application binary interface.
                  Not all setup scripts include this string.

Finally, this command form invokes the QEMU emulator

         $ runqemu qemuarch kernel-image filesystem-image

         Where:
             qemuarch is a string representing the target architecture: qemux86, qemux86-64,
                        qemuppc, qemumips, or qemuarm.

             kernel-image is the architecture-specific kernel image.

             filesystem-image is the .ext3 filesystem image.

Continuing with the example, the following two commands setup the emulation environment and launch QEMU. This example assumes the root filesystem (`.ext3` file) and the pre-built kernel image file both reside in your home directory. The kernel and filesystem are for a 32-bit target architecture.

         $ cd $HOME
         $ source &YOCTO_ADTPATH_DIR;/environment-setup-i586-poky-linux
         $ runqemu qemux86 bzImage-qemux86.bin \
         core-image-sato-qemux86.ext3

The environment in which QEMU launches varies depending on the filesystem image and on the target architecture. For example, if you source the environment for the ARM target architecture and then boot the minimal QEMU image, the emulator comes up in a new shell in command-line mode. However, if you boot the SDK image, QEMU comes up with a GUI.

Booting the PPC image results in QEMU launching in the same shell in command-line mode.