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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>
This commit is contained in:
Scott Rifenbark 2013-06-14 17:10:46 +03:00 committed by Richard Purdie
parent 26a9dd8c29
commit 07c9405365
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documentation/ref-manual/technical-details.xml
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@ -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>