ref-manual: New section on cross-development toolchains added.

First draft of this new section.  It included a figure so the
figure had to be added to the "figures" folder of the
mega-manual.

New section introduces concepts behind the types of cross-toolchains
YP develops through user commands that build images and build the
relocatable SDK.

(From yocto-docs rev: b3c9a2e3f90892a2175110393a962fd152316ca6)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

3 files changed, 174 insertions, 0 deletions

diff --git a/documentation/mega-manual/figures/cross-development-toolchains.png b/documentation/mega-manual/figures/cross-development-toolchains.png
new file mode 100644
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+++ b/documentation/mega-manual/figures/cross-development-toolchains.png
diff --git a/documentation/ref-manual/figures/cross-development-toolchains.png b/documentation/ref-manual/figures/cross-development-toolchains.png
new file mode 100644
index 0000000000..d36670a198
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diff --git a/documentation/ref-manual/technical-details.xml b/documentation/ref-manual/technical-details.xml
index 0634f5702d..f17291f2cb 100644
--- a/documentation/ref-manual/technical-details.xml
+++ b/documentation/ref-manual/technical-details.xml
@@ -153,6 +153,180 @@
     </section>
 </section>
 
+<section id="cross-development-toolchain-generation">
+    <title>Cross-Development Toolchain Generation</title>
+
+    <para>
+        The Yocto Project does most of the work for you when it comes to
+        creating
+        <ulink url='&YOCTO_DOCS_DEV_URL;#cross-development-toolchain'>cross-development toolchains</ulink>.
+        This section provides some technical background information on how
+        cross-development toolchains are created and used.
+        For more information on these toolchain, you can also see the
+        <ulink url='&YOCTO_DOCS_ADT_URL;'>the Yocto Project Application Developer's Guide</ulink>.
+    </para>
+
+    <para>
+        In the Yocto Project development environment, cross-development
+        toolchains are used to build the image and applications that run on the
+        target hardware.
+        With just a few commands, the OpenEmbedded build system creates
+        these necessary toolchains for you.
+    </para>
+
+    <para>
+        The following figure shows a high-level build environment regarding
+        toolchain construction and use.
+    </para>
+
+    <para>
+        <imagedata fileref="figures/cross-development-toolchains.png" width="8in" depth="6in" align="center" />
+    </para>
+
+    <para>
+        Most of the work occurs on the Build Host.
+        This is the machine used to build images and generally work within the
+        the Yocto Project environment.
+        When you run BitBake to create an image, the OpenEmbedded build system
+        uses the host <filename>gcc</filename> compiler to bootstrap a
+        cross-compiler named <filename>gcc-cross</filename>.
+        The <filename>gcc-cross</filename> compiler is what BitBake uses to
+        compile source files when creating the target image.
+        You can think of <filename>gcc-cross</filename> simply as an
+        automatically generated cross-compiler that is used internally within
+        BitBake only.
+    </para>
+
+    <para>
+        The chain of events that occurs when <filename>gcc-cross</filename> is
+        bootstrapped is as follows:
+        <literallayout class='monospaced'>
+     gcc -> binutils-cross -> gcc-cross-initial -> linux_libc-headers -> eglibc-initial -> eglibc -> gcc-cross -> gcc-runtime
+        </literallayout>
+        <itemizedlist>
+            <listitem><para><filename>gcc</filename>:
+                The build host's GNU Compiler Collection (GCC).
+                </para></listitem>
+            <listitem><para><filename>binutils-cross</filename>:
+                The bare minimum binary utilities needed in order to run
+                the <filename>gcc-cross-initial</filename> phase of the
+                bootstrap operation.
+                </para></listitem>
+            <listitem><para><filename>gcc-cross-initial</filename>:
+                An early stage of the bootstrap process for creating
+                the cross-compiler.
+                This stage builds enough of the <filename>gcc-cross</filename>,
+                the C library, and other pieces needed to finish building the
+                final cross-compiler in later stages.
+                This tool is a "native" package (i.e. it is designed to run on
+                the build host).
+                </para></listitem>
+            <listitem><para><filename>linux_libc-headers</filename>:
+                Headers needed for the cross-compiler.
+                </para></listitem>
+            <listitem><para><filename>eglibc-initial</filename>:
+                An initial version of the Embedded GLIBC needed to bootstrap
+                <filename>eglibc</filename>.
+                </para></listitem>
+            <listitem><para><filename>gcc-cross</filename>:
+                The final stage of the bootstrap process for the
+                cross-compiler.
+                This stage results in the actual cross-compiler that
+                BitBake uses when it builds an image for a targeted
+                device.
+                <note>
+                    If you are replacing this cross compiler toolchain
+                    with a custom version, you must replace
+                    <filename>gcc-cross</filename>.
+                </note>
+                This tool is also a "native" package (i.e. it is
+                designed to run on the build host).
+                </para></listitem>
+            <listitem><para><filename>gcc-runtime</filename>:
+                Runtime libraries resulting from the toolchain bootstrapping
+                process.
+                This tool produces a binary that consists of the
+                runtime libraries need for the targeted device.
+                </para></listitem>
+        </itemizedlist>
+    </para>
+
+    <para>
+        You can use the OpenEmbedded build system to build an installer for
+        the relocatable SDK used to develop applications.
+        When you run the installer, it installs the toolchain, which contains
+        the development tools (e.g., the
+        <filename>gcc-cross-canadian</filename>),
+        <filename>binutils-cross-canadian</filename>, and other
+        <filename>nativesdk-*</filename> tools you need to cross-compile and
+        test your software.
+        The figure shows the commands you use to easily build out this
+        toolchain.
+        This cross-development toolchain is built to execute on the
+        <filename>SDKMACHINE</filename>, which might or might not be the same
+        machine as the Build Host.
+        <note>
+            If your target architecture is supported by the Yocto Project,
+            you can take advantage of pre-built images that ship with the
+            Yocto Project and already contain cross-development toolchain
+            installers.
+        </note>
+    </para>
+
+    <para>
+        Here is the bootstrap process for the relocatable toolchain:
+        <literallayout class='monospaced'>
+     gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux_libc-headers -> eglibc-initial -> nativesdk-eglibc -> gcc-crosssdk -> gcc-cross-canadian
+        </literallayout>
+        <itemizedlist>
+            <listitem><para><filename>gcc</filename>:
+                The build host's GNU Compiler Collection (GCC).
+                </para></listitem>
+            <listitem><para><filename>binutils-crosssdk</filename>:
+                The bare minimum binary utilities needed in order to run
+                the <filename>gcc-crosssdk-initial</filename> phase of the
+                bootstrap operation.
+                </para></listitem>
+            <listitem><para><filename>gcc-crosssdk-initial</filename>:
+                An early stage of the bootstrap process for creating
+                the cross-compiler.
+                This stage builds enough of the
+                <filename>gcc-crosssdk</filename> and supporting pieces so that
+                the final stage of the bootstrap process can produce the
+                finished cross-compiler.
+                This tool is a "native" binary that runs on the build host.
+                </para></listitem>
+            <listitem><para><filename>linux_libc-headers</filename>:
+                Headers needed for the cross-compiler.
+                </para></listitem>
+            <listitem><para><filename>eglibc-initial</filename>:
+                An initial version of the Embedded GLIBC needed to bootstrap
+                <filename>nativesdk-eglibc</filename>.
+                </para></listitem>
+            <listitem><para><filename>nativesdk-eglibc</filename>:
+                The Embedded GLIBC needed to bootstrap the
+                <filename>gcc-crosssdk</filename>.
+                </para></listitem>
+            <listitem><para><filename>gcc-crosssdk</filename>:
+                The final stage of the bootstrap process for the
+                relocatable cross-compiler.
+                The <filename>gcc-crosssdk</filename> is a transitory compiler
+                and never leaves the build host.
+                Its purpose is to help in the bootstrap process to create the
+                eventual relocatable <filename>gcc-cross-canadian</filename>
+                compiler, which is relocatable.
+                This tool is also a "native" package (i.e. it is
+                designed to run on the build host).
+                </para></listitem>
+            <listitem><para><filename>gcc-cross-canadian</filename>:
+                The final relocatable cross-compiler.
+                When run on the <filename>SDKMACHINE</filename>, this tool
+                produces executable code that runs on the target device.
+                </para></listitem>
+        </itemizedlist>
+    </para>
+</section>
+
 <section id="shared-state-cache">
     <title>Shared State Cache</title>