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sdk-manual: Updates to the "Makefile-Based Projects" section.

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I wrote the section to include a flow diagram using "make" and
provided a working example highlighting how to override environment
variables.

(From yocto-docs rev: 00e8e09a51a1f0305317f38975a9d7695c92bdb5)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2018-06-07 09:26:41 -07:00
committed by Richard Purdie
parent e8127d4fc4
commit b15903d61b
1 changed files with 104 additions and 41 deletions
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documentation/sdk-manual/sdk-working-projects.xml
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@@ -233,56 +233,118 @@
<title>Makefile-Based Projects</title> <title>Makefile-Based Projects</title>
<para> <para>
For Makefile-based projects, the cross-toolchain environment Simple Makefile-based projects use and interact with the
variables established by running the cross-toolchain environment cross-toolchain environment variables established when you run
setup script are subject to general <filename>make</filename> the cross-toolchain environment setup script.
rules. The environment variables are subject to general
<filename>make</filename> rules.
</para> </para>
<para> <para>
To illustrate this, consider the following four cross-toolchain This section presents a simple Makefile development flow and
provides an example that lets you see how you can use
cross-toolchain environment variables to replace or override
variables used in your Makefile.
<imagedata fileref="figures/sdk-makefile-flow.png" width="6in" height="7in" align="center" />
</para>
<para>
The main point of this section is to explain the following three
cases regarding variable behavior:
<itemizedlist>
<listitem><para>
<emphasis>Case 1 - No Variables Set in the
<filename>Makefile</filename> that Map to Equivalent
Environment Variables Set in the SDK Setup Script:</emphasis>
Because matching variables are not specifically set in the
<filename>Makefile</filename>, the variables retain their
values based on the environment setup script.
</para></listitem>
<listitem><para>
<emphasis>Case 2 - Variables Are Set in the Makefile that
Map to Equivalent Environment Variables from the SDK
Setup Script:</emphasis>
Specifically setting matching variables in the
<filename>Makefile</filename> during the build results in
the environment settings of the variables being
overwritten.
In this case, the variables you set in the
<filename>Makefile</filename> are used.
</para></listitem>
<listitem><para>
<emphasis>Case 3 - Variables Are Set Using the Command Line
that Map to Equivalent Environment Variables from the
SDK Setup Script:</emphasis>
Executing the <filename>Makefile</filename> from the
command line results in the environment settings of the
variables being overwritten.
In this case, the command-line content is used.
<note>
The one exception to this is if you use the following
command-line option:
<literallayout class='monospaced'>
$ make -e <replaceable>target</replaceable>
</literallayout>
Using the "-e" option with <filename>make</filename>
causes the environment variables to be used during
the build.
</note>
</para></listitem>
</itemizedlist>
</para>
<para>
The remainder of this section presents a simple Makefile example
that demonstrates these variable behaviors.
</para>
<para>
In a new shell environment variables are not established for the
SDK until you run the setup script.
For example, the following commands show null values for four
variables that are set when you run the SDK environment setup
script for a 64-bit build host and an i586-tuned target
architecture for a <filename>core-image-sato</filename> image
using the current &DISTRO; Yocto Project release:
<literallayout class='monospaced'>
$ echo ${CC}
$ echo ${LD}
$ echo ${CFLAGS}
$ echo ${CXXFLAGS}
</literallayout>
Running the setup script and then echoing the variables shows the
values established for the SDK:
<literallayout class='monospaced'>
$ source /opt/poky/2.5/environment-setup-i586-poky-linux
$ echo ${CC}
i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
$ echo ${LD}
i586-poky-linux-ld --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
$ echo ${CFLAGS}
-O2 -pipe -g -feliminate-unused-debug-types
$ echo ${CXXFLAGS}
-O2 -pipe -g -feliminate-unused-debug-types
</literallayout>
</para>
<para role='writernotes'>
NEED REST OF THE EXAMPLE.
WORKING ON GETTING IT TO WORK PROPERLY.
</para>
<!--
To illustrate this, consider the following four cross-toolchain
environment variables: environment variables:
<literallayout class='monospaced'> <literallayout class='monospaced'>
<ulink url='&YOCTO_DOCS_REF_URL;#var-CC'>CC</ulink>="i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux" <ulink url='&YOCTO_DOCS_REF_URL;#var-CC'>CC</ulink>="i586-poky-linux-gcc -m32 -march=i586 &DASH;&DASH;sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
<ulink url='&YOCTO_DOCS_REF_URL;#var-LD'>LD</ulink>="i586-poky-linux-ld --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux" <ulink url='&YOCTO_DOCS_REF_URL;#var-LD'>LD</ulink>="i586-poky-linux-ld &DASH;&DASH;sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
<ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types" <ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types"
<ulink url='&YOCTO_DOCS_REF_URL;#var-CXXFLAGS'>CXXFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types" <ulink url='&YOCTO_DOCS_REF_URL;#var-CXXFLAGS'>CXXFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types"
</literallayout> </literallayout>
Now, consider the following three cases: Now, consider the following three cases:
<itemizedlist>
<listitem><para>
<emphasis>Case 1 - No Variables Set in the
<filename>Makefile</filename>:</emphasis>
Because these variables are not specifically set in the
<filename>Makefile</filename>, the variables retain their
values based on the environment.
</para></listitem>
<listitem><para>
<emphasis>Case 2 - Variables Set in the
<filename>Makefile</filename>:</emphasis>
Specifically setting variables in the
<filename>Makefile</filename> during the build results in
the environment settings of the variables being
overwritten.
</para></listitem>
<listitem><para>
<emphasis>Case 3 - Variables Set when the
<filename>Makefile</filename> is Executed from the
Command Line:</emphasis>
Executing the <filename>Makefile</filename> from the
command-line results in the variables being overwritten
with command-line content regardless of what is being set
in the <filename>Makefile</filename>.
In this case, environment variables are not considered
unless you use the "-e" flag during the build:
<literallayout class='monospaced'>
$ make -e <replaceable>file</replaceable>
</literallayout>
If you use this flag, then the environment values of the
variables override any variables specifically set in the
<filename>Makefile</filename>.
</para></listitem>
</itemizedlist>
<note> <note>
For information on the variables set up by the cross-toolchain For information on the variables set up by the cross-toolchain
environment setup script, see the environment setup script, see the
@@ -290,6 +352,7 @@
section. section.
</note> </note>
</para> </para>
-->
</section> </section>
</chapter> </chapter>
<!-- <!--