path: root/documentation/poky-ref-manual/development.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id="platdev">
<title>Platform Development with the Yocto Project</title>

    <section id="platdev-appdev">
    <title>Application Development Using the Yocto Project</title>
    <para>
        The Yocto Project supports several methods of application development through which 
        you can create user-space software designed to run on an embedded device that uses
        a Linux Yocto image developed with the Yocto Project. 
        This flexibility allows you to choose the method that works best for you.  
        This chapter describes each development method.
    </para>

        <section id="platdev-appdev-devshell">
        <title>Development Within a Development Shell</title>

        <para>
            When debugging certain commands or even when just editing packages, 
            <filename>devshell</filename> can be a useful tool.
            Using <filename>devshell</filename> differs from the example shown in the previous 
            section in that when you invoke <filename>devshell</filename> source files are 
            extracted into your working directory and patches are applied. 
            Then, a new terminal is opened and you are placed in the working directory.
            In the new terminal all the Yocto Project build-related environment variables are 
            still defined so you can use commands such as <filename>configure</filename> and 
            <filename>make</filename>. 
            The commands execute just as if the Yocto Project build system were executing them. 
            Consequently, working this way can be helpful when debugging a build or preparing 
            software to be used with the Yocto Project build system.
        </para>

        <para>
            Following is an example that uses <filename>devshell</filename> on a target named
            <filename>matchbox-desktop</filename>:
        </para>

        <para>
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
            </literallayout>
        </para>

        <para>
            This command opens a terminal with a shell prompt within the Poky 
            environment. 
            The following occurs:
            <itemizedlist>
                <listitem><para>The <filename>PATH</filename> variable includes the 
                    cross-toolchain.</para></listitem>
                <listitem><para>The <filename>pkgconfig</filename> variables find the correct 
                    <filename>.pc</filename> files.</para></listitem>
                <listitem><para>The <filename>configure</filename> command finds the 
                    Yocto Project site files as well as any other necessary files.</para></listitem>
            </itemizedlist>
            Within this environment, you can run <filename>configure</filename>
            or <filename>compile</filename> commands as if they were being run by 
            the Yocto Project build system itself.
            As noted earlier, the working directory also automatically changes to the 
            source directory (<filename><link linkend='var-S'>S</link></filename>).
        </para>

        <para> 
            When you are finished, you just exit the shell or close the terminal window.
        </para>

        <para>
            The default shell used by <filename>devshell</filename> is xterm. 
            For examples of available options, see the "UI/Interaction Configuration"
            section of the  
            <filename>meta/conf/bitbake.conf</filename> configuration file in the Yocto Project
            files. 
        </para>

        <para>
            Because an external shell is launched rather than opening directly into the 
            original terminal window, it allows easier interaction with BitBake's multiple
            threads as well as accomodates a future client/server split.
        </para>

        <note>
            <para>It is worth remembering that when using <filename>devshell</filename>
            you need to use the full compiler name such as <filename>arm-poky-linux-gnueabi-gcc</filename> 
            instead of just using <filename>gcc</filename>.
            The same applies to other applications such as <filename>binutils</filename>, 
            <filename>libtool</filename> and so forth.
            BitBake sets up environment variables such as <filename>CC</filename>
            to assist applications, such as <filename>make</filename> to find the correct tools.</para>
            <para>It is also worth noting that <filename>devshell</filename> still works over
            X11 forwarding and similar situations</para>
        </note>
        </section>

        <section id="platdev-appdev-srcrev">
        <title>Development Within Yocto Project for a Package that Uses 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 Yocto Project build system notice new changes added to the 
            SCM and then build the package that depends on them using the latest version. 
            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 in the build directory of the Yocto Project files:
            <literallayout class='monospaced'>
     SRCREV_pn-&lt;PN&gt; = "${AUTOREV}"
            </literallayout>
            where <filename>PN</filename> 
            is the name of the package for which you want to enable automatic source 
            revision updating.
        </para>
        </section>
    </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 help 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 "<link linkend='ref-images'>Reference: Images</link>" appendix 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 the Yocto Project 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, the Yocto Project can 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
                need to be available.
                There are a number of ways you can make these 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, Yocto Project 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 by the Yocto Project.</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 Yocto Project 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><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></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. 
        In the Yocto Project you can achieve this by setting the 
        <filename><link linkend='var-SELECTED_OPTIMIZATION'>SELECTED_OPTIMIZATION
        </link></filename> variable to 
        <filename>-fexpensive-optimizations -fno-omit-framepointer -frename-registers -O2</filename>. 
        You can also achieve it by setting the
        <filename><link linkend='var-DEBUG_BUILD'>DEBUG_BUILD</link></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 Yocto Project file's 
                <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 Yocto Project 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 Yocto Project's 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 Yocto Project, that file is usually located in 
                <filename>/boot/vmlinux-KERNELVERSION</filename>, where 
                <filename>KERNEL-version</filename> is the version of the kernel. 
                The Yocto Project 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 Yocto Project 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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