path: root/documentation/dev-manual/dev-manual-common-tasks.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes standard tasks such as adding new
        software packages, extending or customizing images, and porting work to
        new hardware (adding a new machine). 
        The chapter also describes how to combine multiple 
        versions of library files into a single image, how to handle a package name alias, and
        gives advice about how to make changes to the Yocto Project to achieve the best results.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The OpenEmbedded build system supports organizing <link linkend='metadata'>metadata</link> 
            into multiple layers. 
            Layers allow you to isolate different types of customizations from each other.
            You might find it tempting to keep everything in one layer when working on a single project.
            However, the more modular you organize your metadata, the easier it is to cope with future changes.
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider machine customizations.
            These types of customizations typically reside in a BSP Layer.
            Furthermore, the machine customizations should be isolated from recipes and metadata that support 
            a new GUI environment, for example. 
            This situation gives you a couple of layers: one for the machine configurations, and one for the 
            GUI environment.
            It is important to understand, however, that the BSP layer can still make machine-specific 
            additions to recipes within the GUI environment layer without polluting the GUI layer itself 
            with those machine-specific changes. 
            You can accomplish this through a recipe that is a BitBake append 
            (<filename>.bbappend</filename>) file, which is described later in this section.
        </para>

        <para>
        </para>

        <section id='yocto-project-layers'>
            <title>Layers</title>

            <para>
                The source directory contains several layers right out of the box.
                You can easily identify a layer in the source directory by its folder name.
                Folders that are layers begin with the string <filename>meta</filename>.
                For example, when you set up the <link linkend='source-directory'>source directory</link>
                structure, you will see several layers: <filename>meta</filename>, 
                <filename>meta-hob</filename>, <filename>meta-skeleton</filename>, 
                <filename>meta-yocto</filename>, and <filename>meta-yocto-bsp</filename>.
                Each of these folders is a layer.
            </para>

            <para>
                Furthermore, if you set up a local copy of the <filename>meta-intel</filename> Git repository
                and then explore that folder, you will discover many BSP layers within the 
                <filename>meta-intel</filename> layer.
                For more information on BSP layers, see the 
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP) Developer's Guide.
            </para>
        </section>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layer to use with the OpenEmbedded build system.
                Follow these general steps to create your layer:
                <orderedlist>
                    <listitem><para><emphasis>Check Existing Layers:</emphasis> Before creating a new layer, 
                        you should be sure someone has not already created a layer containing the metadata 
                        you need.
                        You can see the
                        <ulink url='&OE_HOME_URL;/wiki/LayerIndex'><filename>LayerIndex</filename></ulink>
                        for a list of layers from the OpenEmbedded community that can be used in the 
                        Yocto Project.</para></listitem>
                    <listitem><para><emphasis>Create a Directory:</emphasis> Create the directory 
                        for your layer.
                        Traditionally, prepend the name of the folder with the string
                        <filename>meta</filename>.
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Create a Layer Configuration File:</emphasis> Inside your new
                       layer folder, you need to create a <filename>conf/layer.conf</filename> file.
                       It is easiest to take an existing layer configuration file and copy that to your 
                       layer's <filename>conf</filename> directory and then modify the file as needed.</para>
                       <para>The <filename>meta-yocto/conf/layer.conf</filename> file demonstrates the 
                       required syntax:
                       <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH := "${LAYERDIR}:${BBPATH}"

     # We have recipes-* directories, add to BBFILES
     BBFILES := "${BBFILES} ${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yocto"
     BBFILE_PATTERN_yocto := "^${LAYERDIR}/"
     BBFILE_PRIORITY_yocto = "5" 
                        </literallayout></para>
                        <para>In the previous example, the recipes for the layers are added to 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>. 
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
                        variable is then appended with the layer name. 
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename> 
                        variable is set to a regular expression and is used to match files
                        from <filename>BBFILES</filename> into a particular layer.
                        In this case, immediate expansion of 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename> 
                        sets <filename>BBFILE_PATTERN</filename> to the layer's path.
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename> 
                        variable then assigns a priority to the layer. 
                        Applying priorities is useful in situations where the same package might appear in multiple
                        layers and allows you to choose what layer should take precedence.</para>
                        <para>Note the use of the 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename> 
                        variable with the immediate expansion operator.
                        The <filename>LAYERDIR</filename> variable expands to the directory of the current layer and
                        requires the immediate expansion operator so that BitBake does not wait to expand the variable 
                        when it's parsing a different directory.</para>
                        <para>Through the use of the <filename>BBPATH</filename> variable,
                        BitBake locates <filename>.bbclass</filename> files, configuration
                        files, and files that are included with <filename>include</filename> 
                        and <filename>require</filename> statements. 
                        For these cases, BitBake uses the first file with the matching name found in 
                        <filename>BBPATH</filename>.
                        This is similar to the way the <filename>PATH</filename> variable is used for binaries. 
                        We recommend, therefore, that you use unique <filename>.bbclass</filename>
                        and configuration file names in your custom layer.</para></listitem>
                    <listitem><para><emphasis>Add Content:</emphasis> Depending on the type of layer, 
                        add the content.
                        If the layer adds support for a machine, add the machine configuration in 
                        a <filename>conf/machine/</filename> file within the layer.
                        If the layer adds distro policy, add the distro configuration in a
                        <filename>conf/distro/</filename> file with the layer.
                        If the layer introduces new recipes, put the recipes you need in 
                        <filename>recipes-*</filename> subdirectories within the layer.
                        <note>In order to be compliant with the Yocto Project, a layer must contain
                            a <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-readme'>README file.</ulink>
                            </note></para></listitem>
                </orderedlist>
            </para>

            <para>
                To create layers that are easier to maintain, you should consider the following:
                <itemizedlist>
                    <listitem><para>Avoid "overlaying" entire recipes from other layers in your 
                        configuration.
                        In other words, don't copy an entire recipe into your layer and then modify it.
                        Use <filename>.bbappend</filename> files to override the parts of the 
                        recipe you need to modify.</para></listitem>
                    <listitem><para>Avoid duplicating include files.
                        Use <filename>.bbappend</filename> files for each recipe that uses an include 
                        file.
                        Or, if you are introducing a new recipe that requires the included file, use the 
                        path relative to the original layer directory to refer to the file.
                        For example, use <filename>require recipes-core/somepackage/somefile.inc</filename>
                        instead of <filename>require somefile.inc</filename>. 
                        If you're finding you have to overlay the include file, it could indicate a 
                        deficiency in the include file in the layer to which it originally belongs.
                        If this is the case, you need to address that deficiency instead of overlaying
                        the include file.
                        For example, consider how Qt 4 database support plugins are configured.
                        The source directory does not have 
                        MySQL or PostgreSQL, however OpenEmbedded's
                        layer <filename>meta-oe</filename> does.
                        Consequently, <filename>meta-oe</filename> uses <filename>.bbappend</filename>
                        files to modify the <filename>QT_SQL_DRIVER_FLAGS</filename> variable to enable 
                        the appropriate plugins. 
                        This variable was added to the <filename>qt4.inc</filename> include file in 
                        the source directory specifically to allow the <filename>meta-oe</filename> layer
                        to be able to control which plugins are built.</para></listitem>
                </itemizedlist> 
            </para>

            <para>
                We also recommend the following:
                <itemizedlist>
                    <listitem><para>Store custom layers in a Git repository that uses the 
                        <filename>meta-&lt;layer_name&gt;</filename> format.</para></listitem>
                    <listitem><para>Clone the repository alongside other <filename>meta</filename>
                        directories in the 
                        <link linkend='source-directory'>source directory</link>.</para></listitem>
                 </itemizedlist>
                 Following these recommendations keeps your source directory and 
                 its configuration entirely inside the Yocto Project's core base.
            </para>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                Before the OpenEmbedded build system can use your new layer, you need to enable it.
                To enable your layer, simply add your layer's path to the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename> 
                variable in your <filename>conf/bblayers.conf</filename> file, which is found in the 
                <link linkend='build-directory'>build directory</link>. 
                The following example shows how to enable a layer named <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       /path/to/poky/meta \
       /path/to/poky/meta-yocto \
       /path/to/poky/meta-yocto-bsp \
       /path/to/poky/meta-mylayer \
       "                
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file as specified in the 
                <filename>BBLAYERS</filename> variable within the <filename>conf/bblayers.conf</filename>
                file.
                During the processing of each <filename>conf/layer.conf</filename> file, BitBake adds the 
                recipes, classes and configurations contained within the particular layer to the source
                directory.
                <note>
                    Removing the <filename>meta-yocto</filename> layer exposes a bug for the 
                    current release of the Yocto Project.
                    If for some reason you do remove this layer from the 
                    <filename>bblayers.conf</filename>, you must set the 
                    <filename>LCONF_VERSION</filename> variable to "5".
                    See <ulink url='https://bugzilla.yoctoproject.org/show_bug.cgi?id=3176'>[YOCTO_#3176]</ulink>
                    for more information.</note>
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files</title>

            <para>
                Recipes used to append metadata to other recipes are called BitBake append files.
                BitBake append files use the <filename>.bbappend</filename> file type suffix, while  
                the corresponding recipes to which metadata is being appended use the 
                <filename>.bb</filename> file type suffix.
            </para>

            <para>
                A <filename>.bbappend</filename> file allows your layer to make additions or 
                changes to the content of another layer's recipe without having to copy the other 
                recipe into your layer.
                Your <filename>.bbappend</filename> file resides in your layer, while the underlying 
                <filename>.bb</filename> recipe file to which you are appending metadata
                resides in a different layer.
            </para>

            <para>
                Append files files must have the same name as the corresponding recipe.
                For example, the append file <filename>someapp_&DISTRO;.bbappend</filename> must 
                apply to <filename>someapp_&DISTRO;.bb</filename>.
                This means the original recipe and append file names are version number specific.
                If the corresponding recipe is renamed to update to a newer version, the 
                underlying <filename>.bbappend</filename> file must be renamed as well.
                During the build process, BitBake displays an error on starting if it detects a 
                <filename>.bbappend</filename> file that does not have a corresponding recipe 
                with a matching name.
            </para>

            <para>
                Being able to append information to an existing recipe not only avoids duplication, 
                but also automatically applies recipe changes in a different layer to your layer.
                If you were copying recipes, you would have to manually merge changes as they occur.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a corresponding formfactor 
                append file both from the 
                <link linkend='source-directory'>source directory</link>.
                Here is the main formfactor recipe, which is named <filename>formfactor_0.0.bb</filename> and  
                located in the meta layer at <filename>meta/recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     DESCRIPTION = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                         file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r20"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
     	# Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
     	if [ -s "${S}/machconfig" ]; then
     	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
     	fi
     }
                </literallayout>
                Here is the append file, which is named <filename>formfactor_0.0.bbappend</filename> and is from the 
                Crown Bay BSP Layer named <filename>meta-intel/meta-crownbay</filename>.
                The file is in <filename>recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 
     PRINC = "1"
                </literallayout>
                This example adds or overrides files in 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                within a <filename>.bbappend</filename> by extending the path BitBake uses to search for files. 
                The most reliable way to do this is by prepending the 
                <filename>FILESEXTRAPATHS</filename> variable.
                For example, if you have your files in a directory that is named the same as your package 
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>),
                you can add this directory by adding the following to your <filename>.bbappend</filename> file:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </literallayout>
                Using the immediate expansion assignment operator <filename>:=</filename> is important because 
                of the reference to <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that items in the list remain 
                colon-separated.
                <note>BitBake automatically defines the <filename>THISDIR</filename> variable.
                    You should never set this variable yourself.
                    Using <filename>_prepend</filename> ensures your path will be searched prior to other 
                    paths in the final list.
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there are recipe files with 
                the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher priority number taking precedence.
                Priority values also affect the order in which multiple <filename>.bbappend</filename> files 
                for the same recipe are applied. 
                You can either specify the priority manually, or allow the build system to calculate it
                based on the layer's dependencies.
            </para>

            <para>
                To specify the layer's priority manually, use the 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable.
                For example:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY := "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the precedence order of 
                <filename>.conf</filename> or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                You can use the BitBake layer management tool to provide a view into the structure of 
                recipes across a multi-layer project.
                Being able to generate output that reports on configured layers with their paths and 
                priorities and on <filename>.bbappend</filename> files and their applicable recipes
                can help to reveal potential problems.
            </para>

            <para>
                Use the following form when running the layer management tool.
                <literallayout class='monospaced'>
     $ bitbake-layers &lt;command&gt; [arguments]
                </literallayout>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para><filename><emphasis>help:</emphasis></filename>
                        Displays general help or help on a specified command.</para></listitem>
                    <listitem><para><filename><emphasis>show-layers:</emphasis></filename>
                        Show the current configured layers.</para></listitem>
                    <listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
                        Lists available recipes and the layers that provide them.  
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
                        Lists overlayed recipes.  
                        A recipe is overlayed when a recipe with the same name exists in another layer 
                        that has a higher layer priority.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-appends:</emphasis></filename>
                        Lists <filename>.bbappend</filename> files and the recipe files to which
                        they apply.</para></listitem>
                    <listitem><para><filename><emphasis>flatten:</emphasis></filename>
                        Flattens the layer configuration into a separate output directory.
                        Flattening your layer configuration builds a "flattened" directory that contains
                        the contents of all layers, with any overlayed recipes removed and any
                        <filename>.bbappend</filename> files appended to the corresponding recipes.
                        You might have to perform some manual cleanup of the flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>Non-recipe files (such as patches) are overwritten.
                                The flatten command shows a warning for these files.</para></listitem>
                            <listitem><para>Anything beyond the normal layer setup has been added to 
                                the <filename>layer.conf</filename> file.
                                Only the lowest priority layer's <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>Overridden and appended items from <filename>.bbappend</filename>
                                files need to be cleaned up.
                                The contents of each <filename>.bbappend</filename> end up in the 
                                flattened recipe.
                                However, if there are appended or changed variable values, you need to tidy 
                                these up yourself.
                                Consider the following example.
                                Here, the <filename>bitbake-layers</filename> command adds the line
                                <filename>#### bbappended ...</filename> so that you know where the following
                                lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout></para></listitem>
                        </itemizedlist></para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize images to satisfy particular requirements. 
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                One way to get additional software into an image is to create a custom image. 
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                By creating a custom image, a developer has total control
                over the contents of the image. 
                It is important to use the correct names of packages in the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename> 
                variable. 
                You must use the OpenEmbedded notation and not the Debian notation for the names 
                (e.g. <filename>eglibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                The other method for creating a custom image is to base it on an existing image. 
                For example, if you want to create an image based on <filename>core-image-sato</filename>
                but add the additional package <filename>strace</filename> to the image, 
                copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a 
                new <filename>.bb</filename> and add the following line to the end of the copy:
                <literallayout class='monospaced'>
     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Package Groups</title>

            <para>
                For complex custom images, the best approach is to create a custom package group recipe
                that is used to build the image or images. 
                A good example of a package group recipe is 
                <filename>meta/recipes-core/packagegroups/packagegroup-core-boot.bb</filename>.
                The 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> 
                variable lists the package group packages you wish to produce. <filename>inherit packagegroup</filename>
                sets appropriate default values and automatically adds <filename>-dev</filename>
                and <filename>-dbg</filename> complementary
                packages for every package specified in <filename>PACKAGES</filename>. 
                Note that the inherit line should be towards
                the top of the recipe, certainly before you set <filename>PACKAGES</filename>.
                For each package you specify in <filename>PACKAGES</filename>, you can use 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename> 
                entries to provide a list of packages the parent task package should contain. 
                Following is an example:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two package group packages are created with their dependencies and their
                recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and 
                <filename>packagegroup-custom-tools</filename>. 
                To build an image using these package group packages, you need to add 
                <filename>packagegroup-custom-apps</filename> and/or 
                <filename>packagegroup-custom-tools</filename> to 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and 
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                Ultimately users might want to add extra image features to the set by using the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'>IMAGE_FEATURES</ulink></filename>
                variable. 
                To create these features, the best reference is 
                <filename>meta/classes/core-image.bbclass</filename>, which shows how this is 
                achieved. 
                In summary, the file looks at the contents of the 
                <filename>IMAGE_FEATURES</filename>
                variable and then maps that into a set of tasks or packages. 
                Based on this information, the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'> IMAGE_INSTALL</ulink></filename> 
                variable is generated automatically. 
                Users can add extra features by extending the class or creating a custom class for use 
                with specialized image <filename>.bb</filename> files.
                You can also add more features by configuring the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'>EXTRA_IMAGE_FEATURES</ulink></filename>
                variable in the <filename>local.conf</filename> file found in the source directory
                located in the build directory.
            </para>

            <para>
                The Yocto Project ships with two SSH servers you can use in your images: 
                Dropbear and OpenSSH. 
                Dropbear is a minimal SSH server appropriate for resource-constrained environments,
                while OpenSSH is a well-known standard SSH server implementation.
                By default, the <filename>core-image-sato</filename> image is configured to use Dropbear.
                The <filename>core-image-basic</filename> and <filename>core-image-lsb</filename>
                images both include OpenSSH.
                The <filename>core-image-minimal</filename> image does not contain an SSH server.
                To change these defaults, edit the <filename>IMAGE_FEATURES</filename> variable
                so that it sets the image you are working with to include 
                <filename>ssh-server-dropbear</filename> or <filename>ssh-server-openssh</filename>.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                It is possible to customize image contents by using variables from your
                local configuration in your <filename>conf/local.conf</filename> file. 
                Because it is limited to local use, this method generally only allows you to 
                add packages and is not as flexible as creating your own customized image.
                When you add packages using local variables this way, you need to realize that 
                these variable changes affect all images at the same time and might not be
                what you require.
            </para>

            <para>
                The simplest way to add extra packages to all images is by using the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable with the <filename>_append</filename> operator:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                </literallayout>
                Use of the syntax is important.
                Specifically, the space between the quote and the package name, which is
                <filename>strace</filename> in this example.
                This space is required since the <filename>_append</filename>
                operator does not add the space.
            </para>

            <para>
                Furthermore, you must use <filename>_append</filename> instead of the <filename>+=</filename> 
                operator if you want to avoid ordering issues. 
                The reason for this is because doing so unconditionally appends to the variable and 
                avoids ordering problems due to the variable being set in image recipes and 
                <filename>.bbclass</filename> files with operators like <filename>?=</filename>.
                Using <filename>_append</filename> ensures the operation takes affect.
            </para>

            <para>
                As shown in its simplest use, <filename>IMAGE_INSTALL_append</filename> affects
                all images.
                It is possible to extend the syntax so that the variable applies to a specific image only.
                Here is an example:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </literallayout>
                This example adds <filename>strace</filename> to <filename>core-image-minimal</filename>
                only.
            </para>

            <para>
                You can add packages using a similar approach through the  
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename> 
                variable.
                If you use this variable, only <filename>core-image-*</filename> images are affected.
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-addpkg'>
        <title>Adding a Package</title>

        <para>
            To add a package you need to write a recipe for it. 
            Writing a recipe means creating a <filename>.bb</filename> file that sets some
            variables.
            For information on variables that are useful for recipes and for information about recipe naming
            issues, see the 
            "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>" 
            section of the Yocto Project Reference Manual.
        </para>

        <para>
            Before writing a recipe from scratch, it is often useful to check
            whether someone else has written one already. 
            OpenEmbedded is a good place to look as it has a wider scope and range of packages.
            Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes 
            you find there should work for you.
        </para>

        <para>
            For new packages, the simplest way to add a recipe is to base it on a similar
            pre-existing recipe. 
            The sections that follow provide some examples that show how to add standard 
            types of packages.
        </para>

        <section id='usingpoky-extend-addpkg-singlec'>
            <title>Single .c File Package (Hello World!)</title>

            <para>
                Building an application from a single file that is stored locally (e.g. under 
                <filename>files/</filename>) requires a recipe that has the file listed in 
                the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                variable. 
                Additionally, you need to manually write the <filename>do_compile</filename> and
                <filename>do_install</filename> tasks.
                The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> 
                variable defines the 
                directory containing the source code, which is set to 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'>
                WORKDIR</ulink></filename> in this case - the directory BitBake uses for the build.
                <literallayout class='monospaced'>
     DESCRIPTION = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
     PR = "r0"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                </literallayout>
            </para>

            <para>
                By default, the <filename>helloworld</filename>, <filename>helloworld-dbg</filename>,
                and <filename>helloworld-dev</filename> packages are built. 
                For information on how to customize the packaging process, see the
                "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application
                into Multiple Packages</link>" section.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-autotools'>
            <title>Autotooled Package</title>
            <para>
                Applications that use Autotools such as <filename>autoconf</filename> and 
                <filename>automake</filename> require a recipe that has a source archive listed in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and 
                also inherits Autotools, which instructs BitBake to use the
                <filename>autotools.bbclass</filename> file, which contains the definitions of all the steps
                needed to build an Autotool-based application.
                The result of the build is automatically packaged. 
                And, if the application uses NLS for localization, packages with local information are 
                generated (one package per language). 
                Following is one example: (<filename>hello_2.3.bb</filename>)
                <literallayout class='monospaced'>
     DESCRIPTION = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
     PR = "r0"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                 </literallayout>
            </para>

            <para>
                The variable 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename> 
                is used to track source license changes as described in the
                "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Track License Changes</ulink>" section. 
                You can quickly create Autotool-based recipes in a manner similar to the previous example.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-makefile'>
            <title>Makefile-Based Package</title>

            <para>
                Applications that use GNU <filename>make</filename> also require a recipe that has
                the source archive listed in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>. 
                You do not need to add a <filename>do_compile</filename> step since by default BitBake 
                starts the <filename>make</filename> command to compile the application. 
                If you need additional <filename>make</filename> options you should store them in the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'>EXTRA_OEMAKE</ulink></filename>
                variable.
                BitBake passes these options into the <filename>make</filename> GNU invocation. 
                Note that a <filename>do_install</filename> task is still required.
                Otherwise, BitBake runs an empty <filename>do_install</filename> task by default. 
            </para>

            <para>
                Some applications might require extra parameters to be passed to the compiler.
                For example, the application might need an additional header path. 
                You can accomplish this by adding to the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                The following example shows this:
                <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                </literallayout>
            </para>

            <para>
            In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                <literallayout class='monospaced'>
     DESCRIPTION = "Tools for managing memory technology devices."
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                    file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \
	     	file://add-exclusion-to-mkfs-jffs2-git-2.patch"

     S = "${WORKDIR}/git/"

     PR = "r1"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' \
        'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
	     oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
            INCLUDEDIR=${includedir}
	     install -d ${D}${includedir}/mtd/
	     for f in ${S}/include/mtd/*.h; do
	     	install -m 0644 $f ${D}${includedir}/mtd/
	     done
     }

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                </literallayout>
            </para>

            <para>
                If your sources are available as a tarball instead of a Git repository, you
                will need to provide the URL to the tarball as well as an 
                <filename>md5</filename> or <filename>sha256</filename> sum of
                the download. 
                Here is an example:
                <literallayout class='monospaced'>
     SRC_URI="ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.4.9.tar.bz2"
     SRC_URI[md5sum]="82b8e714b90674896570968f70ca778b"
                </literallayout>
                You can generate the <filename>md5</filename> or <filename>sha256</filename> sums 
                by using the <filename>md5sum</filename> or <filename>sha256sum</filename> commands
                with the target file as the only argument. 
                Here is an example:
                <literallayout class='monospaced'>
     $ md5sum mtd-utils-1.4.9.tar.bz2 
     82b8e714b90674896570968f70ca778b mtd-utils-1.4.9.tar.bz2
                </literallayout>
            </para>
        </section>

        <section id='splitting-an-application-into-multiple-packages'>
            <title>Splitting an Application into Multiple Packages</title>

            <para>                        
                You can use the variables 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename> 
                to split an application into multiple packages.
            </para>

            <para>
                Following is an example that uses the <filename>libXpm</filename> recipe. 
                By default, this recipe generates a single package that contains the library along 
                with a few binaries.  
                You can modify the recipe to split the binaries into separate packages:
                <literallayout class='monospaced'>
     require xorg-lib-common.inc

     DESCRIPTION = "X11 Pixmap library"
     LICENSE = "X-BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
     DEPENDS += "libxext libsm libxt"
     PR = "r3"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                </literallayout>
            </para>

            <para>
                In the previous example, we want to ship the <filename>sxpm</filename>
                and <filename>cxpm</filename> binaries in separate packages. 
                Since <filename>bindir</filename> would be packaged into the main 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename> 
                package by default, we prepend the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink>
                </filename> variable so additional package names are added to the start of list. 
                This results in the extra 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink>_*</filename>
                variables then containing information that define which files and
                directories go into which packages. 
                Files included by earlier packages are skipped by latter packages.
                Thus, the main 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename> package 
                does not include the above listed files.
            </para>
        </section>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>                        
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the 
                built library.  
            </para>

            <para>
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
                variables in the 
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable contains 
                <filename>${PN}-staticdev</filename>, which includes all static library files.
                <note>
                    Previously released versions of the Yocto Project defined the static library files 
                    through <filename>${PN}-dev</filename>.
                </note>
                Following, is part of the BitBake configuration file. 
                You can see where the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
     PACKAGES_DYNAMIC = "${PN}-locale-*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"
     
     FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"
     
     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-postinstalls'>
            <title>Post Install Scripts</title>

            <para>
                To add a post-installation script to a package, add a <filename>pkg_postinst_PACKAGENAME()
                </filename> function to the <filename>.bb</filename> file and use 
                <filename>PACKAGENAME</filename> as the name of the package you want to attach to the 
                <filename>postinst</filename> script.
                Normally 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                can be used, which automatically expands to <filename>PACKAGENAME</filename>.
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is called when the 
                root filesystem is created. 
                If the script succeeds, the package is marked as installed. 
                If the script fails, the package is marked as unpacked and the script is
                executed when the image boots again.
            </para>

            <para>
                Sometimes it is necessary for the execution of a post-installation
                script to be delayed until the first boot.  
                For example, the script might need to be executed on the device itself. 
                To delay script execution until boot time, use the following structure in the 
                post-installation script:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                </literallayout>
            </para>

            <para>
                The previous example delays execution until the image boots again because the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'>D</ulink></filename> 
                variable points
                to the directory containing the image when the root filesystem is created at build time but
                is unset when executed on the first boot. 
            </para>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Adding a New Machine</title>

        <para>
            Adding a new machine to the Yocto Project is a straightforward process. 
            This section provides information that gives you an idea of the changes you must make.
            The information covers adding machines similar to those the Yocto Project already supports. 
            Although well within the capabilities of the Yocto Project, adding a totally new architecture 
            might require 
            changes to <filename>gcc/eglibc</filename> and to the site information, which is 
            beyond the scope of this manual.
        </para>

        <para>
            For a complete example that shows how to add a new machine, 
            see the 
            "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>" 
            in the Yocto Project Board Support Package (BSP) Developer's Guide.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a machine configuration you need to add a <filename>.conf</filename> file
                with details of the device being added to the <filename>conf/machine/</filename> file.
                The name of the file determines the name the OpenEmbedded build system
                uses to reference the new machine.
            </para>

            <para>
                The most important variables to set in this file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>
                        TARGET_ARCH</ulink></filename> (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>
                        PREFERRED_PROVIDER</ulink></filename>_virtual/kernel (see below)</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>
                        MACHINE_FEATURES</ulink></filename> (e.g. "apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para> 
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLE'>
                        SERIAL_CONSOLE</ulink></filename> (e.g. "115200 ttyS0")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>
                        KERNEL_IMAGETYPE</ulink></filename> (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>
                        IMAGE_FSTYPES</ulink></filename> (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para> 
                You can find full details on these variables in the reference section. 
                You can leverage many existing machine <filename>.conf</filename> files from 
                <filename>meta/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The OpenEmbedded build system needs to be able to build a kernel for the machine. 
                You need to either create a new kernel recipe for this machine, or extend an 
                existing recipe. 
                You can find several kernel examples in the 
                source directory at <filename>meta/recipes-kernel/linux</filename>
                that you can use as references.
            </para>

            <para>
                If you are creating a new recipe, normal recipe-writing rules apply for setting 
                up a 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>. 
                Thus, you need to specify any necessary patches and set 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> to point at the source code. 
                You need to create a <filename>configure</filename> task that configures the 
                unpacked kernel with a defconfig.
                You can do this by using a <filename>make defconfig</filename> command or,
                more commonly, by copying in a suitable <filename>defconfig</filename> file and and then running 
                <filename>make oldconfig</filename>. 
                By making use of <filename>inherit kernel</filename> and potentially some of the 
                <filename>linux-*.inc</filename> files, most other functionality is 
                centralized and the the defaults of the class normally work well.
            </para>

            <para>
                If you are extending an existing kernel, it is usually a matter of adding a 
                suitable defconfig file.
                The file needs to be added into a location similar to defconfig files
                used for other machines in a given kernel. 
                A possible way to do this is by listing the file in the 
                <filename>SRC_URI</filename> and adding the machine to the expression in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the 
                target hardware for which the image is being built and information that 
                the build system cannot obtain from other sources such as the kernel.  
                Some examples of information contained in a formfactor configuration file include 
                framebuffer orientation, whether or not the system has a keyboard, 
                the positioning of the keyboard in relation to the screen, and 
                the screen resolution.
            </para>

            <para>
                The build system uses reasonable defaults in most cases, but if customization is 
                necessary you need to create a <filename>machconfig</filename> file 
                in the <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as 
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the 
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area. 
                Following is an example for qemuarm:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

    <section id="building-multiple-architecture-libraries-into-one-image">
        <title>Combining Multiple Versions of Library Files into One Image</title>

        <para>
            The build system offers the ability to build libraries with different
            target optimizations or architecture formats and combine these together
            into one system image. 
            You can link different binaries in the image 
            against the different libraries as needed for specific use cases.
            This feature is called "Multilib."
        </para>

        <para>
            An example would be where you have most of a system compiled in 32-bit
            mode using 32-bit libraries, but you have something large, like a database
            engine, that needs to be a 64-bit application and use 64-bit libraries.
            Multilib allows you to get the best of both 32-bit and 64-bit libraries.
        </para>

        <para>
            While the Multilib feature is most commonly used for 32 and 64-bit differences,
            the approach the build system uses facilitates different target optimizations. 
            You could compile some binaries to use one set of libraries and other binaries
            to use other different sets of libraries.
            The libraries could differ in architecture, compiler options, or other 
            optimizations.
        </para>

        <para>
            This section overviews the Multilib process only. 
            For more details on how to implement Multilib, see the 
            <ulink url='&YOCTO_WIKI_URL;/wiki/Multilib'>Multilib</ulink> wiki 
            page.
        </para>

        <section id='preparing-to-use-multilib'>
            <title>Preparing to use Multilib</title>

            <para>
                User-specific requirements drive the Multilib feature,
                Consequently, there is no one "out-of-the-box" configuration that likely
                exists to meet your needs.
            </para>

            <para>
                In order to enable Multilib, you first need to ensure your recipe is
                extended to support multiple libraries. 
                Many standard recipes are already extended and support multiple libraries.
                You can check in the <filename>meta/conf/multilib.conf</filename>
                configuration file in the source directory to see how this is 
                done using the 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
                variable.
                Eventually, all recipes will be covered and this list will be unneeded.
            </para>
  
            <para>
                For the most part, the Multilib class extension works automatically to
                extend the package name from <filename>${PN}</filename> to
                <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                is the particular multilib (e.g. "lib32-" or "lib64-"). 
                Standard variables such as 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>, 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                <filename>RPROVIDES</filename>, 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                and <filename>PACKAGES_DYNAMIC</filename> are automatically extended by the system.
                If you are extending any manual code in the recipe, you can use the 
                <filename>${MLPREFIX}</filename> variable to ensure those names are extended 
                correctly. 
                This automatic extension code resides in <filename>multilib.bbclass</filename>.
            </para>
        </section>

        <section id='using-multilib'>
            <title>Using Multilib</title>

            <para>
                After you have set up the recipes, you need to define the actual
                combination of multiple libraries you want to build. 
                You accomplish this through your <filename>local.conf</filename>
                configuration file in the 
                <link linkend='build-directory'>build directory</link>. 
                An example configuration would be as follows:
                <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL = "lib32-connman"
                </literallayout>
                This example enables an
                additional library named <filename>lib32</filename> alongside the 
                normal target packages.
                When combining these "lib32" alternatives, the example uses "x86" for tuning.
                For information on this particular tuning, see
                <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
            </para>

            <para>
                The example then includes <filename>lib32-connman</filename>
                in all the images, which illustrates one method of including a 
                multiple library dependency. 
                You can use a normal image build to include this dependency,
                for example:
                <literallayout class='monospaced'>
     $ bitbake core-image-sato
                </literallayout>
                You can also build Multilib packages specifically with a command like this:
                <literallayout class='monospaced'>
     $  bitbake lib32-connman
                </literallayout>
            </para>
        </section>

        <section id='additional-implementation-details'>
            <title>Additional Implementation Details</title>

            <para>
                Different packaging systems have different levels of native Multilib
                support. 
                For the RPM Package Management System, the following implementation details 
                exist:
                <itemizedlist>
                    <listitem><para>A unique architecture is defined for the Multilib packages,
                        along with creating a unique deploy folder under 
                        <filename>tmp/deploy/rpm</filename> in the 
                        <link linkend='build-directory'>build directory</link>. 
                        For example, consider <filename>lib32</filename> in a 
                        <filename>qemux86-64</filename> image. 
                        The possible architectures in the system are "all", "qemux86_64",
                        "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                    <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from 
                        <filename>${PN}</filename> during RPM packaging.
                        The naming for a normal RPM package and a Multilib RPM package in a
                        <filename>qemux86-64</filename> system resolves to something similar to
                        <filename>bash-4.1-r2.x86_64.rpm</filename> and 
                        <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                        </para></listitem>
                    <listitem><para>When installing a Multilib image, the RPM backend first 
                        installs the base image and then installs the Multilib libraries.
                        </para></listitem>
                    <listitem><para>The build system relies on RPM to resolve the identical files in the 
                        two (or more) Multilib packages.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                For the IPK Package Management System, the following implementation details exist:
                <itemizedlist>
                    <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from 
                        <filename>${PN}</filename> during IPK packaging.
                        The naming for a normal RPM package and a Multilib IPK package in a
                        <filename>qemux86-64</filename> system resolves to something like 
                        <filename>bash_4.1-r2.x86_64.ipk</filename> and
                        <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                        </para></listitem>
                    <listitem><para>The IPK deploy folder is not modified with 
                        <filename>${MLPREFIX}</filename> because packages with and without 
                        the Multilib feature can exist in the same folder due to the 
                        <filename>${PN}</filename> differences.</para></listitem>
                    <listitem><para>IPK defines a sanity check for Multilib installation 
                        using certain rules for file comparison, overridden, etc.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section> 
    </section>

    <section id='configuring-the-kernel'>
        <title>Configuring the Kernel</title>

        <para>
            Configuring the Yocto Project kernel consists of making sure the <filename>.config</filename>
            file has all the right information in it for the image you are building.
            You can use the <filename>menuconfig</filename> tool and configuration fragments to 
            make sure your <filename>.config</filename> file is just how you need it. 
            This section describes how to use <filename>menuconfig</filename>, create and use 
            configuration fragments, and how to interactively tweak your <filename>.config</filename>
            file to create the leanest kernel configuration file possible.
        </para>

        <para>
            For concepts on kernel configuration, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_URL;#kernel-configuration'>Kernel Configuration</ulink>"
            section in the Yocto Project Kernel Architecture and Use Manual.
        </para>

        <section id='using-menuconfig'>
            <title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>
 
            <para>
                The easiest way to define kernel configurations is to set them through the
                <filename>menuconfig</filename> tool.
                For general information on <filename>menuconfig</filename>, see
                <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
            </para>

            <para>
                To use the <filename>menuconfig</filename> tool in the Yocto Project development
                environment, you must build the tool using BitBake.
                The following commands build and invoke <filename>menuconfig</filename> assuming the 
                source directory top-level folder is <filename>~/poky</filename>:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
                Once <filename>menuconfig</filename> comes up, its standard interface allows you to 
                examine and configure all the kernel configuration parameters.
                Once you have made your changes, simply exit the tool and save your changes to 
                create an updated version of the <filename>.config</filename> configuration file.
            </para>

            <para>
                For an example that shows how to change a specific kernel option
                using <filename>menuconfig</filename>, see the 
                "<link linkend='changing-the-config-smp-configuration-using-menuconfig'>Changing
                the <filename>CONFIG_SMP</filename> Configuration Using <filename>menuconfig</filename></link>" 
                section.
            </para>
        </section>

        <section id='creating-config-fragments'>
            <title>Creating Configuration Fragments</title>

            <para>
                Configuration fragments are simply kernel options that appear in a file
                placed where the OpenEmbedded build system can find and apply them.
                Syntactically, the configuration statement is identical to what would appear
                in the <filename>.config</filename> file, which is in the 
                <link linkend='build-directory'>build directory</link> in 
                <filename>tmp/work/&lt;arch&gt;-poky-linux/linux-yocto-&lt;release-specific-string&gt;/linux-&lt;arch&gt;-&lt;build-type&gt;</filename>.
            </para>

            <para>
                It is simple to create a configuration fragment.  
                For example, issuing the following from the shell creates a configuration fragment
                file named <filename>my_smp.cfg</filename> that enables multi-processor support
                within the kernel:
                <literallayout class='monospaced'>
     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                </literallayout>
                <note>
                    All configuration files must use the <filename>.cfg</filename> extension in order
                    for the OpenEmbedded build system to recognize them as a configuration fragment.
                </note>
            </para>

            <para>
                Where do you put your configuration files?
                You can place these configuration files in the same area pointed to by  
                <filename>SRC_URI</filename>.
                The OpenEmbedded build system will pick up the configuration and add it to the 
                kernel's configuration.
                For example, suppose you had a set of configuration options in a file called 
                <filename>myconfig.cfg</filename>.  
                If you put that file inside a directory named <filename>/linux-yocto</filename> 
                that resides in the same directory as the kernel's append file and then add 
                a <filename>SRC_URI</filename> statement such as the following to the kernel's append file, 
                those configuration options will be picked up and applied when the kernel is built.
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg"
                </literallayout>
            </para>

            <para>
                As mentioned earlier, you can group related configurations into multiple files and 
                name them all in the <filename>SRC_URI</filename> statement as well.
                For example, you could group separate configurations specifically for Ethernet and graphics
                into their own files and add those by using a <filename>SRC_URI</filename> statement like the 
                following in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
        </section>

        <section id='fine-tuning-the-kernel-configuration-file'>
            <title>Fine-tuning the Kernel Configuration File</title>

            <para>
                You can make sure the <filename>.config</filename> is as lean or efficient as 
                possible by reading the output of the kernel configuration fragment audit,
                noting any issues, making changes to correct the issues, and then repeating.
            </para>

            <para>
                As part of the kernel build process, the 
                <filename>kernel_configcheck</filename> task runs.
                This task validates the kernel configuration by checking the final 
                <filename>.config</filename> file against the input files.
                During the check, the task produces warning messages for the following 
                issues:
                <itemizedlist>
                    <listitem><para>Requested options that did not make the final 
                        <filename>.config</filename> file.</para></listitem>
                    <listitem><para>Configuration items that appear twice in the same 
                        configuration fragment.</para></listitem>
                    <listitem><para>Configuration items tagged as 'required' were overridden.
                        </para></listitem>
                    <listitem><para>A board overrides a non-board specific option.</para></listitem>
                    <listitem><para>Listed options not valid for the kernel being processed. 
                        In other words, the option does not appear anywhere.</para></listitem>
                </itemizedlist>
                <note>
                    The <filename>kernel_configcheck</filename> task can also optionally report
                    if an option is overridden during processing.
                </note>
            </para>

            <para>
                For each output warning, a message points to the file
                that contains a list of the options and a pointer to the config
                fragment that defines them.
                Collectively, the files are the key to streamlining the configuration.
            </para>

            <para>
                To streamline the configuration, do the following:
                <orderedlist>
                    <listitem><para>Start with a full configuration that you know
                        works - it builds and boots successfully.
                        This configuration file will be your baseline.</para></listitem>
                    <listitem><para>Separately run the <filename>configme</filename> and 
                        <filename>kernel_configcheck</filename> tasks.</para></listitem>
                    <listitem><para>Take the resulting list of files from the 
                        <filename>kernel_configcheck</filename> task warnings and do the following:
                        <itemizedlist>
                            <listitem><para>Drop values that are redefined in the fragment but do not
                                change the final <filename>.config</filename> file.</para></listitem>
                            <listitem><para>Analyze and potentially drop values from the 
                                <filename>.config</filename> file that override required 
                                configurations.</para></listitem>
                            <listitem><para>Analyze and potentially remove non-board specific options.
                                </para></listitem>
                            <listitem><para>Remove repeated and invalid options.</para></listitem>
                        </itemizedlist></para></listitem>
                    <listitem><para>After you have worked through the output of the kernel configuration 
                        audit, you can re-run the <filename>configme</filename> 
                        and <filename>kernel_configcheck</filename> tasks to see the results of your 
                        changes. 
                        If you have more issues, you can deal with them as described in the 
                        previous step.</para></listitem>
                </orderedlist> 
            </para>

            <para>
                Iteratively working through steps two through four eventually yields 
                a minimal, streamlined configuration file.
                Once you have the best <filename>.config</filename>, you can build the Linux
                Yocto kernel.
            </para>
        </section>
    </section>

    <section id="usingpoky-changes-updatingimages">
        <title>Updating Existing Images</title>

        <para>
            Often, rather than re-flashing a new image, you might wish to install updated 
            packages into an existing running system. 
            You can do this by first sharing the <filename>tmp/deploy/ipk/</filename> directory
            through a web server and then by changing <filename>/etc/opkg/base-feeds.conf</filename> 
            to point at the shared server.
            Following is an example:
            <literallayout class='monospaced'>
     $ src/gz all http://www.mysite.com/somedir/deploy/ipk/all
     $ src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a
     $ src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard
            </literallayout>
        </para>
    </section>

    <section id="usingpoky-changes-prbump">
        <title>Incrementing a Package Revision Number</title>

        <para>
            If a committed change results in changing the package output,
            then the value of the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename> 
            variable needs to be increased 
            (or "bumped") as part of that commit. 
            For new recipes you should add the <filename>PR</filename>
            variable and set its initial value equal to "r0", which is the default.  
            Even though the default value is "r0", the practice of adding it to a new recipe makes 
            it harder to forget to bump the variable when you make changes 
            to the recipe in future.
        </para>

        <para>
            If you are sharing a common <filename>.inc</filename> file with multiple recipes, 
            you can also use the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename> 
            variable to ensure that 
            the recipes sharing the <filename>.inc</filename> file are rebuilt when the 
            <filename>.inc</filename> file itself is changed. 
            The <filename>.inc</filename> file must set <filename>INC_PR</filename>
            (initially to "r0"), and all recipes referring to it should set <filename>PR</filename>
            to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed.
            If the <filename>.inc</filename> file is changed then its 
            <filename>INC_PR</filename> should be incremented.
        </para>

        <para> 
            When upgrading the version of a package, assuming the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename> 
            changes, the <filename>PR</filename> variable should be reset to "r0"
            (or "$(INC_PR).0" if you are using <filename>INC_PR</filename>).
        </para>

        <para>
            Usually, version increases occur only to packages.
            However, if for some reason <filename>PV</filename> changes but does not 
            increase, you can increase the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename> 
            variable (Package Epoch).
            The <filename>PE</filename> variable defaults to "0".
        </para>

        <para>
            Version numbering strives to follow the 
            <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
            Debian Version Field Policy Guidelines</ulink>.
            These guidelines define how versions are compared and what "increasing" a version means.
        </para>

        <para>
            There are two reasons for following the previously mentioned guidelines.
            First, to ensure that when a developer updates and rebuilds, they get all the changes to
            the repository and do not have to remember to rebuild any sections.
            Second, to ensure that target users are able to upgrade their
            devices using package manager commands such as <filename>opkg upgrade</filename> 
            (or similar commands for dpkg/apt or rpm-based systems). 
        </para>

        <para>
            The goal is to ensure the Yocto Project has packages that can be upgraded in all cases.
        </para>
    </section>

    <section id="usingpoky-configuring-DISTRO_PN_ALIAS">
        <title>Handling a Package Name Alias</title>
        <para>
            Sometimes a package name you are using might exist under an alias or as a similarly named
            package in a different distribution.
            The OpenEmbedded build system implements a <filename>distro_check</filename>
            task that automatically connects to major distributions
            and checks for these situations. 
            If the package exists under a different name in a different distribution, you get a 
            <filename>distro_check</filename> mismatch.  
            You can resolve this problem by defining a per-distro recipe name alias using the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_PN_ALIAS'>DISTRO_PN_ALIAS</ulink></filename> 
            variable.
        </para>

        <para>
            Following is an example that shows how you specify the <filename>DISTRO_PN_ALIAS</filename>
            variable:
            <literallayout class='monospaced'>
     DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                       distro2=package_name_alias2 \
                                       distro3=package_name_alias3 \
                                       ..."
            </literallayout>
        </para>
        
        <para>
            If you have more than one distribution alias, separate them with a space.
            Note that the build system currently automatically checks the 
            Fedora, OpenSuSE, Debian, Ubuntu, 
            and Mandriva distributions for source package recipes without having to specify them 
            using the <filename>DISTRO_PN_ALIAS</filename> variable.
            For example, the following command generates a report that lists the Linux distributions
            that include the sources for each of the recipes.
            <literallayout class='monospaced'>
     $ bitbake world -f -c distro_check
            </literallayout>
            The results are stored in the <filename>build/tmp/log/distro_check-${DATETIME}.results</filename> 
            file found in the source directory.
        </para>
    </section>

    <section id="building-software-from-an-external-source">
        <title>Building Software from an External Source</title>

        <para>
            By default, the OpenEmbedded build system does its work from within the 
            <link linkend='build-directory'>build directory</link>.  
            The build process involves fetching the source files, unpacking them, and then patching them
            if necessary before the build takes place.
        </para>

        <para>
            Situations exist where you might want to build software from source files that are external to 
            and thus outside of the <link linkend='source-directory'>source directory</link>.
            For example, suppose you have a project that includes a new BSP with a heavily customized 
            kernel, a very minimal image, and some new user-space recipes.
            And, you want to minimize exposing the build system to the 
            development team so that they can focus on their project and maintain everyone's workflow
            as much as possible.
            In this case, you want a kernel source directory on the development machine where the 
            development occurs.
            You want the recipe's 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
            variable to point to the external directory and use it as is, not copy it.  
        </para>

        <para>
            To build from software that comes from an external source, all you need to do is
            change your recipe so that it inherits the 
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></ulink> 
            class and then sets the 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
            variable to point to your external source code.
            Here are the statements to put in your recipe:
            <literallayout class='monospaced'>
     inherit externalsrc
     S = "/some/path/to/your/package/source"
            </literallayout>
        </para>

        <para>
            It is important to know that the <filename>externalsrc.bbclass</filename> assumes that the 
            source directory <filename>S</filename> and the build directory 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink>
            are different even though by default these directories are the same.
            This assumption is important because it supports building different variants of the recipe
            by using the 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
            variable.
            You could allow the build directory to be the same as the source directory but you would 
            not be able to build more than one variant of the recipe.
            Consequently, if you are building multiple variants of the recipe, you need to establish a 
            build directory that is different than the source directory.
        </para>
    </section>

    <section id='excluding-recipes-from-the-build'>
        <title>Excluding Recipes From the Build</title>

        <para>
            You might find that there are groups of recipes you want to filter 
            out of the build process.
            For example, recipes you know you will never use or want should not 
            be part of the build.
            Removing these recipes from parsing speeds up parts of the build.
        </para>

        <para>
            It is possible to filter or mask out <filename>.bb</filename> and 
            <filename>.bbappend</filename> files. 
            You can do this by providing an expression with the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBMASK'>BBMASK</ulink></filename> 
            variable. 
            Here is an example:
            <literallayout class='monospaced'>
     BBMASK = ".*/meta-mymachine/recipes-maybe/"
            </literallayout>
            Here, all <filename>.bb</filename> and <filename>.bbappend</filename> files
            in the directory that match the expression are ignored during the build
            process.
        </para>
    </section>

    <section id="platdev-appdev-srcrev">
        <title>Using an External SCM</title>

        <para>
            If you're working on a recipe that pulls from an external Source Code Manager (SCM), it 
            is possible to have the OpenEmbedded build system notice new recipe changes added to the 
            SCM and then build the resulting package that depends on the new recipes by using the latest 
            versions. 
            This only works for SCMs from which it is possible to get a sensible revision number for changes.
            Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories.
        </para>

        <para>
            To enable this behavior, simply add the following to the <filename>local.conf</filename>
            configuration file found in the 
            <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>build directory</ulink>:
            <literallayout class='monospaced'>
     SRCREV_pn-&lt;PN&gt; = "${AUTOREV}"
            </literallayout>
            where <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> 
            is the name of the recipe for which you want to enable automatic source 
            revision updating.
        </para>
    </section>

    <section id="platdev-gdb-remotedebug">
        <title>Debugging With the GNU Project Debugger (GDB) Remotely</title>

        <para>
            GDB allows you to examine running programs, which in turn helps you to understand and fix problems. 
            It also allows you to perform post-mortem style analysis of program crashes. 
            GDB is available as a package within the Yocto Project and by default is 
            installed in SDK images.
            See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter 
            in the Yocto Project Reference Manual for a description of these images. 
            You can find information on GDB at <ulink url="http://sourceware.org/gdb/"/>.
        </para>

        <tip>
            For best results, install <filename>-dbg</filename> packages for the applications 
            you are going to debug.
            Doing so makes available extra debug symbols that give you more meaningful output.
        </tip>

        <para>
            Sometimes, due to memory or disk space constraints, it is not possible
            to use GDB directly on the remote target to debug applications. 
            These constraints arise because GDB needs to load the debugging information and the 
            binaries of the process being debugged. 
            Additionally, GDB needs to perform many computations to locate information such as function 
            names, variable names and values, stack traces and so forth - even before starting the 
            debugging process. 
            These extra computations place more load on the target system and can alter the
            characteristics of the program being debugged.
        </para>

        <para>
            To help get past the previously mentioned constraints, you can use Gdbserver.
            Gdbserver runs on the remote target and does not load any debugging information 
            from the debugged process.
            Instead, a GDB instance processes the debugging information that is run on a 
            remote computer - the host GDB. 
            The host GDB then sends control commands to Gdbserver to make it stop or start the debugged 
            program, as well as read or write memory regions of that debugged program. 
            All the debugging information loaded and processed as well    
            as all the heavy debugging is done by the host GDB.
            Offloading these processes gives the Gdbserver running on the target a chance to remain 
            small and fast.
        </para>

        <para>
            Because the host GDB is responsible for loading the debugging information and 
            for doing the necessary processing to make actual debugging happen, the 
            user has to make sure the host can access the unstripped binaries complete
            with their debugging information and also be sure the target is compiled with no optimizations. 
            The host GDB must also have local access to all the libraries used by the 
            debugged program. 
            Because Gdbserver does not need any local debugging information, the binaries on
            the remote target can remain stripped. 
            However, the binaries must also be compiled without optimization 
            so they match the host's binaries.
        </para>

        <para>
            To remain consistent with GDB documentation and terminology, the binary being debugged 
            on the remote target machine is referred to as the "inferior" binary.
            For documentation on GDB see the  
            <ulink url="http://sourceware.org/gdb/documentation/">GDB site</ulink>.
        </para>

        <section id="platdev-gdb-remotedebug-launch-gdbserver">
            <title>Launching Gdbserver on the Target</title>

            <para>
                First, make sure Gdbserver is installed on the target. 
                If it is not, install the package <filename>gdbserver</filename>, which needs the 
                <filename>libthread-db1</filename> package.
            </para>

            <para>
                As an example, to launch Gdbserver on the target and make it ready to "debug" a 
                program located at <filename>/path/to/inferior</filename>, connect
                to the target and launch:
                <literallayout class='monospaced'>
     $ gdbserver localhost:2345 /path/to/inferior
                </literallayout>
                Gdbserver should now be listening on port 2345 for debugging
                commands coming from a remote GDB process that is running on the host computer.
                Communication between Gdbserver and the host GDB are done using TCP. 
                To use other communication protocols, please refer to the  
                <ulink url='http://www.gnu.org/software/gdb/'>Gdbserver documentation</ulink>.
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdb">
            <title>Launching GDB on the Host Computer</title>

            <para>
                Running GDB on the host computer takes a number of stages.
                This section describes those stages.
            </para>

            <section id="platdev-gdb-remotedebug-launch-gdb-buildcross">
                <title>Building the Cross-GDB Package</title>
                <para>
                    A suitable GDB cross-binary is required that runs on your host computer but
                    also knows about the the ABI of the remote target. 
                    You can get this binary from the meta-toolchain.
                    Here is an example:
                    <literallayout class='monospaced'> 
     /usr/local/poky/eabi-glibc/arm/bin/arm-poky-linux-gnueabi-gdb
                    </literallayout> 
                    where <filename>arm</filename> is the target architecture and 
                    <filename>linux-gnueabi</filename> the target ABI.
                </para>

                <para>
                    Alternatively, you can use BitBake to build the <filename>gdb-cross</filename> binary. 
                    Here is an example:
                    <literallayout class='monospaced'>
     $ bitbake gdb-cross
                    </literallayout>
                    Once the binary is built, you can find it here: 
                    <literallayout class='monospaced'>
     tmp/sysroots/&lt;host-arch&gt;/usr/bin/&lt;target-abi&gt;-gdb 
                    </literallayout>
                </para>
            </section>

            <section id="platdev-gdb-remotedebug-launch-gdb-inferiorbins">
                <title>Making the Inferior Binaries Available</title>

                <para>
                    The inferior binary (complete with all debugging symbols), as well as any
                    libraries (and their debugging symbols) on which the inferior binary depends,
                    needs to be available.
                    There are a number of ways you can make these items available.
                </para>

                <para>
                    Perhaps the easiest way is to have an SDK image that corresponds to the plain
                    image installed on the device. 
                    In the case of <filename>core-image-sato</filename>, 
                    <filename>core-image-sato-sdk</filename> would contain suitable symbols. 
                    Because the SDK images already have the debugging symbols installed, it is just a 
                    question of expanding the archive to some location and then informing GDB. 
                </para>

                <para>
                    Alternatively, the OpenEmbedded build system can build a custom directory of files 
                    for a specific 
                    debugging purpose by reusing its <filename>tmp/rootfs</filename> directory.
                    This directory contains the contents of the last built image. 
                    This process assumes two things:
                    <itemizedlist>
                        <listitem><para>The image running on the target was the last image to 
                        be built.</para></listitem>
                        <listitem><para>The package (<filename>foo</filename> in the following 
                        example) that contains the inferior binary to be debugged has been built 
                        without optimization and has debugging information available.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    The following steps show how to build the custom directory of files:
                    <orderedlist>
                        <listitem><para>Install the package (<filename>foo</filename> in this case) to 
                            <filename>tmp/rootfs</filename>:
                            <literallayout class='monospaced'>
     $ tmp/sysroots/i686-linux/usr/bin/opkg-cl -f \
     tmp/work/&lt;target-abi&gt;/core-image-sato-1.0-r0/temp/opkg.conf -o \
     tmp/rootfs/ update
                            </literallayout></para></listitem>
                        <listitem><para>Install the debugging information:
                            <literallayout class='monospaced'>
     $ tmp/sysroots/i686-linux/usr/bin/opkg-cl -f \
     tmp/work/&lt;target-abi&gt;/core-image-sato-1.0-r0/temp/opkg.conf \
     -o tmp/rootfs install foo

     $ tmp/sysroots/i686-linux/usr/bin/opkg-cl -f \
     tmp/work/&lt;target-abi&gt;/core-image-sato-1.0-r0/temp/opkg.conf \
     -o tmp/rootfs install foo-dbg
                            </literallayout></para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id="platdev-gdb-remotedebug-launch-gdb-launchhost">
                <title>Launch the Host GDB</title>

                <para>
                    To launch the host GDB, you run the <filename>cross-gdb</filename> binary and provide 
                    the inferior binary as part of the command line.  
                    For example, the following command form continues with the example used in 
                    the previous section.  
                    This command form loads the <filename>foo</filename> binary
                    as well as the debugging information:
                    <literallayout class='monospaced'>
     $ &lt;target-abi&gt;-gdb rootfs/usr/bin/foo
                    </literallayout>
                    Once the GDB prompt appears, you must instruct GDB to load all the libraries
                    of the inferior binary from <filename>tmp/rootfs</filename> as follows:
                    <literallayout class='monospaced'>
     $ set solib-absolute-prefix /path/to/tmp/rootfs
                    </literallayout>
                    The pathname <filename>/path/to/tmp/rootfs</filename> must either be
                    the absolute path to <filename>tmp/rootfs</filename> or the location at which 
                    binaries with debugging information reside.
                </para>

                <para>
                    At this point you can have GDB connect to the Gdbserver that is running 
                    on the remote target by using the following command form:
                    <literallayout class='monospaced'>
     $ target remote remote-target-ip-address:2345
                    </literallayout>
                    The <filename>remote-target-ip-address</filename> is the IP address of the
                    remote target where the Gdbserver is running. 
                    Port 2345 is the port on which the GDBSERVER is running.
                </para>
            </section>

            <section id="platdev-gdb-remotedebug-launch-gdb-using">
                <title>Using the Debugger</title>

                <para>
                    You can now proceed with debugging as normal - as if you were debugging
                    on the local machine.
                    For example, to instruct GDB to break in the "main" function and then 
                    continue with execution of the inferior binary use the following commands
                    from within GDB:
                    <literallayout class='monospaced'>
     (gdb) break main
     (gdb) continue
                    </literallayout>
                </para>

                <para>
                    For more information about using GDB, see the project's online documentation at 
                    <ulink url="http://sourceware.org/gdb/download/onlinedocs/"/>.
                </para>
            </section>
        </section>
    </section>

    <section id="platdev-oprofile">
        <title>Profiling with OProfile</title>

        <para>
            <ulink url="http://oprofile.sourceforge.net/">OProfile</ulink> is a 
            statistical profiler well suited for finding performance 
            bottlenecks in both userspace software and in the kernel. 
            This profiler provides answers to questions like "Which functions does my application spend 
            the most time in when doing X?" 
            Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling 
            applications on target hardware straightforward.
        </para>

        <para>
            To use OProfile, you need an image that has OProfile installed. 
            The easiest way to do this is with <filename>tools-profile</filename> in the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'>IMAGE_FEATURES</ulink></filename> variable. 
            You also need debugging symbols to be available on the system where the analysis
            takes place. 
            You can gain access to the symbols by using <filename>dbg-pkgs</filename> in the
            <filename>IMAGE_FEATURES</filename> variable or by
            installing the appropriate <filename>-dbg</filename> packages. 
        </para>

        <para>
            For successful call graph analysis, the binaries must preserve the frame 
            pointer register and should also be compiled with the 
            <filename>-fno-omit-framepointer</filename> flag. 
            You can achieve this by setting the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SELECTED_OPTIMIZATION'>SELECTED_OPTIMIZATION</ulink></filename>
            variable with the following options:
            <literallayout class='monospaced'>
     -fexpensive-optimizations
     -fno-omit-framepointer
     -frename-registers 
     -O2
            </literallayout> 
            You can also achieve it by setting the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DEBUG_BUILD'>DEBUG_BUILD</ulink></filename> 
            variable to "1" in the <filename>local.conf</filename> configuration file.
            If you use the <filename>DEBUG_BUILD</filename> variable,
            you will also add extra debug information that can make the debug packages large.
        </para>

        <section id="platdev-oprofile-target">
            <title>Profiling on the Target</title>

            <para>
                Using OProfile you can perform all the profiling work on the target device. 
                A simple OProfile session might look like the following:
            </para>

            <para>
                <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
              .
              .
        [do whatever is being profiled]
              .
              .
     # opcontrol --stop
     $ opreport -cl
                </literallayout>
            </para>

            <para>
                In this example, the <filename>reset</filename> command clears any previously profiled data.
                The next command starts OProfile.
                The options used when starting the profiler separate dynamic library data 
                within applications, disable kernel profiling, and enable callgraphing up to
                five levels deep.    
                <note>
                    To profile the kernel, you would specify the 
                    <filename>--vmlinux=/path/to/vmlinux</filename> option.
                    The <filename>vmlinux</filename> file is usually in the source directory in the 
                    <filename>/boot/</filename> directory and must match the running kernel.
                </note>
            </para>

            <para> 
                After you perform your profiling tasks, the next command stops the profiler. 
                After that, you can view results with the <filename>opreport</filename> command with options
                to see the separate library symbols and callgraph information.
            </para>

            <para>
                Callgraphing logs information about time spent in functions and about a function's
                calling function (parent) and called functions (children).
                The higher the callgraphing depth, the more accurate the results.  
                However, higher depths also increase the logging overhead.
                Consequently, you should take care when setting the callgraphing depth. 
                <note>
                    On ARM, binaries need to have the frame pointer enabled for callgraphing to work.
                    To accomplish this use the <filename>-fno-omit-framepointer</filename> option 
                    with <filename>gcc</filename>.
                </note>
            </para>

            <para>
                For more information on using OProfile, see the OProfile 
                online documentation at 
                <ulink url="http://oprofile.sourceforge.net/docs/"/>.
            </para>
        </section>

        <section id="platdev-oprofile-oprofileui">
            <title>Using OProfileUI</title>

            <para>
                A graphical user interface for OProfile is also available. 
                You can download and build this interface from the Yocto Project at
                <ulink url="&YOCTO_GIT_URL;/cgit.cgi/oprofileui/"></ulink>. 
                If the "tools-profile" image feature is selected, all necessary binaries
                are installed onto the target device for OProfileUI interaction.
            </para>

            <para>
                Even though the source directory usually includes all needed patches on the target device, you 
                might find you need other OProfile patches for recent OProfileUI features.
                If so, see the <ulink url='&YOCTO_GIT_URL;/cgit.cgi/oprofileui/tree/README'>
                OProfileUI README</ulink> for the most recent information.
            </para>

            <section id="platdev-oprofile-oprofileui-online">
                <title>Online Mode</title>

                <para>
                    Using OProfile in online mode assumes a working network connection with the target 
                    hardware. 
                    With this connection, you just need to run "oprofile-server" on the device. 
                    By default, OProfile listens on port 4224. 
                    <note>
                        You can change the port using the <filename>--port</filename> command-line 
                        option.
                    </note>
                </para>

                <para>
                    The client program is called <filename>oprofile-viewer</filename> and its UI is relatively 
                    straightforward.
                    You access key functionality through the buttons on the toolbar, which
                    are duplicated in the menus.
                    Here are the buttons:
                    <itemizedlist>
                        <listitem><para><emphasis>Connect:</emphasis> Connects to the remote host.
                            You can also supply the IP address or hostname.</para></listitem>
                        <listitem><para><emphasis>Disconnect:</emphasis> Disconnects from the target.
                            </para></listitem>
                        <listitem><para><emphasis>Start:</emphasis> Starts profiling on the device.
                            </para></listitem>
                        <listitem><para><emphasis>Stop:</emphasis> Stops profiling on the device and 
                            downloads the data to the local host. 
                            Stopping the profiler generates the profile and displays it in the viewer.
                            </para></listitem>
                        <listitem><para><emphasis>Download:</emphasis> Downloads the data from the 
                            target and generates the profile, which appears in the viewer.</para></listitem>
                        <listitem><para><emphasis>Reset:</emphasis> Resets the sample data on the device. 
                            Resetting the data removes sample information collected from previous
                            sampling runs. 
                            Be sure you reset the data if you do not want to include old sample information.
                            </para></listitem>
                        <listitem><para><emphasis>Save:</emphasis> Saves the data downloaded from the
                            target to another directory for later examination.</para></listitem>
                        <listitem><para><emphasis>Open:</emphasis> Loads previously saved data.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    The client downloads the complete 'profile archive' from
                    the target to the host for processing. 
                    This archive is a directory that contains the sample data, the object files, 
                    and the debug information for the object files. 
                    The archive is then converted using the <filename>oparchconv</filename> script, which is 
                    included in this distribution.
                    The script uses <filename>opimport</filename> to convert the archive from
                    the target to something that can be processed on the host.
                </para>

                <para>
                    Downloaded archives reside in the build directory in 
                    <filename>/tmp</filename> and are cleared up when they are no longer in use.
                </para>

                <para>
                    If you wish to perform kernel profiling, you need to be sure 
                    a <filename>vmlinux</filename> file that matches the running kernel is available. 
                    In the source directory, that file is usually located in 
                    <filename>/boot/vmlinux-KERNELVERSION</filename>, where 
                    <filename>KERNEL-version</filename> is the version of the kernel. 
                    The OpenEmbedded build system generates separate <filename>vmlinux</filename> 
                    packages for each kernel it builds.
                    Thus, it should just be a question of making sure a matching package is 
                    installed (e.g. <filename>opkg install kernel-vmlinux</filename>. 
                    The files are automatically installed into development and profiling images 
                    alongside OProfile. 
                    A configuration option exists within the OProfileUI settings page that you can use to 
                    enter the location of the <filename>vmlinux</filename> file. 
                </para>

                <para>
                    Waiting for debug symbols to transfer from the device can be slow, and it
                    is not always necessary to actually have them on the device for OProfile use. 
                    All that is needed is a copy of the filesystem with the debug symbols present 
                    on the viewer system. 
                    The "<link linkend='platdev-gdb-remotedebug-launch-gdb'>Launching GDB on the Host Computer</link>"
                    section covers how to create such a directory with 
                    the source directory and how to use the OProfileUI Settings dialog to specify the location.
                    If you specify the directory, it will be used when the file checksums 
                    match those on the system you are profiling.
                </para>
            </section>

            <section id="platdev-oprofile-oprofileui-offline">
                <title>Offline Mode</title>

                <para>
                    If network access to the target is unavailable, you can generate
                    an archive for processing in <filename>oprofile-viewer</filename> as follows:
                    <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
            .
            .
     [do whatever is being profiled]
            .
            .
     # opcontrol --stop
     # oparchive -o my_archive
                    </literallayout>
                </para>

                <para>
                    In the above example, <filename>my_archive</filename> is the name of the 
                    archive directory where you would like the profile archive to be kept. 
                    After the directory is created, you can copy it to another host and load it
                    using <filename>oprofile-viewer</filename> open functionality.
                    If necessary, the archive is converted.
                </para>
            </section>
        </section>
    </section>
</chapter>

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