source: BOOK/chroot/x86/before-chroot.xml@ 6757ca46

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<sect1 id="ch-chroot-before-chroot">
  <?dbhtml filename="before-chroot.html"?>
  <title>Before Entering the Chroot Environment</title>

  <sect2 role="determining-ifneeded">
    <title>Determining if steps need to be taken</title>

    <para>Before we can enter the chroot we have to make sure that the system is
    in the proper state. From this point on the <envar>${CLFS_TARGET}</envar>
    environment variable will no longer exist, so it will have no bearing on the
    rest of the book - most packages will rely on
    <command>config.guess</command> provided by
    <xref linkend="ch-system-automake"/>. Packages that do not use autotools
    either do not care about the target triplet, or have their own means
    of determining its value.</para>

    <para>In both cases, the information about the host cpu used to determine
    the target triplet is gathered from the same place,
    <command>uname -m</command>. Executing this command outside of the chroot
    as well as inside the chroot will have the exact same output.</para>

   <para>If you're unsure if your host and target have the same target
    triplet, you can use this test to determine what the host's target triplet
    is and if you need to take any steps to ensure that you don't build for the
    wrong architecture. Extract the <xref linkend="ch-system-automake"/> tarball
    and <command>cd</command> into the created directory. Then execute the
    following to see what the detected target triplet is by
    <command>config.guess</command>:</para>

<screen><userinput>lib/config.guess</userinput></screen>

    <para>If the output of that command does not equal what is in
    <envar>${CLFS_TARGET}</envar> then you need to read on. If it does then you
    can safely continue onto <xref linkend="ch-chroot-chroot"/>.</para>

  </sect2>

  <sect2 role="using-setarch">
    <title>Using Setarch</title>

    <para>If your host has a tool called <command>setarch</command>, this may
    solve your problems, at least if you're building for i686. On an
    architecture such as x86_64, using
    <command>setarch linux32 uname -m</command> will only
    ever output i686. It is not possible to get an output of i486 or i586.</para>

    <para>To test if setarch does everything you need it to, execute the
    following command from inside the <xref linkend="ch-system-automake"/>
    directory:</para>

<screen><userinput>setarch linux32 lib/config.guess</userinput></screen>

    <para>If the output of the command above equals what is in
    <envar>${CLFS_TARGET}</envar> then you have a viable solution. You can
    wrap the chroot command on the next page with
    <command>setarch linux32</command>. It will look like the following:</para>

<screen><userinput>setarch linux32 chroot "${CLFS}" /tools/bin/env -i \
    HOME=/root TERM="${TERM}" PS1='\u:\w\$ ' \
    PATH=/bin:/usr/bin:/sbin:/usr/sbin:/tools/bin \
    /tools/bin/bash --login +h</userinput></screen>

    <para>If setarch works for you then you can safely continue onto
    <xref linkend="ch-chroot-chroot"/>. If not, there is one more option
    covered in this book.</para>

  </sect2>

  <sect2 role="using-uname_hack">
    <title>Using a Uname Hack</title>

    <para os="uua">The Uname Hack is a kernel module that modifies the output of
    <command>uname -m</command> by directly changing the value of the
    detected machine type. The kernel module will save the original value
    and restore it when the module is unloaded.</para>

    <variablelist os="uub" role="materials">
      <varlistentry>
        <term>Uname Hack (&uname_hack-version;) - &uname_hack-size;:</term>

        <listitem>
          <para>Home page: <ulink url="&uname_hack-home;"/></para>
          <para>Download: <ulink url="&uname_hack-url;"/></para>
          <para>MD5 sum: <literal>&uname_hack-md5;</literal></para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para os="uuc">Extract the tarball and <command>cd</command> into the
    created directory. To build the Uname Hack you must have the kernel sources
    for your currently running kernel available. Build the Uname Hack with the
    following or similar command:</para>

<screen os="uud"><userinput>make uname_hack_fake_machine=i486</userinput></screen>

    <variablelist os="uue">
      <title>The meaning of the make and install options:</title>

      <varlistentry os="uue1">
        <term><parameter>uname_hack_fake_machine=i486</parameter></term>
        <listitem>
          <para>This parameter sets the value that the uts machine type will be
          changed to. Alternatively this could be set to i586 or i686.</para>
        </listitem>
      </varlistentry>

    </variablelist>

    <para os="uuf">In the top level directory of the Uname Hack package you
    should see a file named <filename>uname_hack.ko</filename>. As soon as
    that module is loaded into the running kernel the output of
    <command>uname -m</command> will be affected immediately system-wide.
    Load the kernel module with the following command:</para>

<screen os="uug"><userinput>insmod uname_hack.ko</userinput></screen>

    <para os="uuh">To test if the Uname Hack is working properly, execute the
    following command from inside the <xref linkend="ch-system-automake"/>
    directory:</para>

<screen os="uui"><userinput>lib/config.guess</userinput></screen>

    <para os="uuj">The output of the above command should be the same as the
    <envar>${CLFS_TARGET}</envar> environment variable. If this is not the
    case, you can try and get help on the CLFS Support Mailing List or the
    IRC Channel. See <xref linkend="ch-intro-askforhelp"/> for more
    information.</para>

  </sect2>

</sect1>