poky/documentation/sdk-manual/working-projects.rst - openbmc/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-SA-2.0-UK

 ********************************
 Using the SDK Toolchain Directly
 ********************************

 You can use the SDK toolchain directly with Makefile and Autotools-based
 projects.

 Autotools-Based Projects
 ========================

 Once you have a suitable :ref:`sdk-manual/intro:the cross-development toolchain`
 installed, it is very easy to develop a project using the `GNU
 Autotools-based <https://en.wikipedia.org/wiki/GNU_Build_System>`__
 workflow, which is outside of the :term:`OpenEmbedded Build System`.

 The following figure presents a simple Autotools workflow.

 .. image:: figures/sdk-autotools-flow.png
    :align: center
    :width: 70%

 Follow these steps to create a simple Autotools-based "Hello World"
 project:

 .. note::

    For more information on the GNU Autotools workflow, see the same
    example on the
    GNOME Developer
    site.

 1. *Create a Working Directory and Populate It:* Create a clean
    directory for your project and then make that directory your working
    location.
    ::

       $ mkdir $HOME/helloworld
       $ cd $HOME/helloworld

    After setting up the directory, populate it with files needed for the flow.
    You need a project source file, a file to help with configuration,
    and a file to help create the Makefile, and a README file:
    ``hello.c``, ``configure.ac``, ``Makefile.am``, and ``README``,
    respectively.

    Use the following command to create an empty README file, which is
    required by GNU Coding Standards::

       $ touch README

    Create the remaining
    three files as follows:

    -  ``hello.c``::

          #include <stdio.h>

          main()
              {
                  printf("Hello World!\n");
              }

    -  ``configure.ac``::

          AC_INIT(hello,0.1)
          AM_INIT_AUTOMAKE([foreign])
          AC_PROG_CC
          AC_CONFIG_FILES(Makefile)
          AC_OUTPUT

    -  ``Makefile.am``::

          bin_PROGRAMS = hello
          hello_SOURCES = hello.c

 2. *Source the Cross-Toolchain Environment Setup File:* As described
    earlier in the manual, installing the cross-toolchain creates a
    cross-toolchain environment setup script in the directory that the
    SDK was installed. Before you can use the tools to develop your
    project, you must source this setup script. The script begins with
    the string "environment-setup" and contains the machine architecture,
    which is followed by the string "poky-linux". For this example, the
    command sources a script from the default SDK installation directory
    that uses the 32-bit Intel x86 Architecture and the &DISTRO; Yocto
    Project release::

       $ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux

    Another example is sourcing the environment setup directly in a Yocto
    build::

       $ source tmp/deploy/images/qemux86-64/environment-setup-core2-64-poky-linux

 3. *Create the configure Script:* Use the ``autoreconf`` command to
    generate the ``configure`` script::

       $ autoreconf

    The ``autoreconf``
    tool takes care of running the other Autotools such as ``aclocal``,
    ``autoconf``, and ``automake``.

    .. note::

       If you get errors from ``configure.ac``, which ``autoreconf``
       runs, that indicate missing files, you can use the "-i" option,
       which ensures missing auxiliary files are copied to the build
       host.

 4. *Cross-Compile the Project:* This command compiles the project using
    the cross-compiler. The
    :term:`CONFIGURE_FLAGS`
    environment variable provides the minimal arguments for GNU
    configure::

       $ ./configure ${CONFIGURE_FLAGS}

    For an Autotools-based
    project, you can use the cross-toolchain by just passing the
    appropriate host option to ``configure.sh``. The host option you use
    is derived from the name of the environment setup script found in the
    directory in which you installed the cross-toolchain. For example,
    the host option for an ARM-based target that uses the GNU EABI is
    ``armv5te-poky-linux-gnueabi``. You will notice that the name of the
    script is ``environment-setup-armv5te-poky-linux-gnueabi``. Thus, the
    following command works to update your project and rebuild it using
    the appropriate cross-toolchain tools::

      $ ./configure --host=armv5te-poky-linux-gnueabi --with-libtool-sysroot=sysroot_dir

 5. *Make and Install the Project:* These two commands generate and
    install the project into the destination directory::

       $ make
       $ make install DESTDIR=./tmp

    .. note::

       To learn about environment variables established when you run the
       cross-toolchain environment setup script and how they are used or
       overridden by the Makefile, see the
       :ref:`sdk-manual/working-projects:makefile-based projects` section.

    This next command is a simple way to verify the installation of your
    project. Running the command prints the architecture on which the
    binary file can run. This architecture should be the same
    architecture that the installed cross-toolchain supports.
    ::

       $ file ./tmp/usr/local/bin/hello

 6. *Execute Your Project:* To execute the project, you would need to run
    it on your target hardware. If your target hardware happens to be
    your build host, you could run the project as follows::

       $ ./tmp/usr/local/bin/hello

    As expected, the project displays the "Hello World!" message.

 Makefile-Based Projects
 =======================

 Simple Makefile-based projects use and interact with the cross-toolchain
 environment variables established when you run the cross-toolchain
 environment setup script. The environment variables are subject to
 general ``make`` rules.

 This section presents a simple Makefile development flow and provides an
 example that lets you see how you can use cross-toolchain environment
 variables and Makefile variables during development.

 .. image:: figures/sdk-makefile-flow.png
    :align: center
    :width: 70%

 The main point of this section is to explain the following three cases
 regarding variable behavior:

 -  *Case 1 --- No Variables Set in the Makefile Map to Equivalent
    Environment Variables Set in the SDK Setup Script:* Because matching
    variables are not specifically set in the ``Makefile``, the variables
    retain their values based on the environment setup script.

 -  *Case 2 --- Variables Are Set in the Makefile that Map to Equivalent
    Environment Variables from the SDK Setup Script:* Specifically
    setting matching variables in the ``Makefile`` during the build
    results in the environment settings of the variables being
    overwritten. In this case, the variables you set in the ``Makefile``
    are used.

 -  *Case 3 --- Variables Are Set Using the Command Line that Map to
    Equivalent Environment Variables from the SDK Setup Script:*
    Executing the ``Makefile`` from the command line results in the
    environment variables being overwritten. In this case, the
    command-line content is used.

 .. note::

    Regardless of how you set your variables, if you use the "-e" option
    with ``make``, the variables from the SDK setup script take precedence::

       $ make -e target


 The remainder of this section presents a simple Makefile example that
 demonstrates these variable behaviors.

 In a new shell environment variables are not established for the SDK
 until you run the setup script. For example, the following commands show
 a null value for the compiler variable (i.e.
 :term:`CC`).
 ::

    $ echo ${CC}

    $

 Running the
 SDK setup script for a 64-bit build host and an i586-tuned target
 architecture for a ``core-image-sato`` image using the current &DISTRO;
 Yocto Project release and then echoing that variable shows the value
 established through the script::

    $ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux
    $ echo ${CC}
    i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux

 To illustrate variable use, work through this simple "Hello World!"
 example:

 1. *Create a Working Directory and Populate It:* Create a clean
    directory for your project and then make that directory your working
    location.
    ::

       $ mkdir $HOME/helloworld
       $ cd $HOME/helloworld

    After
    setting up the directory, populate it with files needed for the flow.
    You need a ``main.c`` file from which you call your function, a
    ``module.h`` file to contain headers, and a ``module.c`` that defines
    your function.

    Create the three files as follows:

    -  ``main.c``::

          #include "module.h"
          void sample_func();
          int main()
          {
              sample_func();
              return 0;
          }

    -  ``module.h``::

          #include <stdio.h>
          void sample_func();

    -  ``module.c``::

          #include "module.h"
          void sample_func()
          {
              printf("Hello World!");
              printf("\n");
          }

 2. *Source the Cross-Toolchain Environment Setup File:* As described
    earlier in the manual, installing the cross-toolchain creates a
    cross-toolchain environment setup script in the directory that the
    SDK was installed. Before you can use the tools to develop your
    project, you must source this setup script. The script begins with
    the string "environment-setup" and contains the machine architecture,
    which is followed by the string "poky-linux". For this example, the
    command sources a script from the default SDK installation directory
    that uses the 32-bit Intel x86 Architecture and the &DISTRO_NAME; Yocto
    Project release::

       $ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux

    Another example is sourcing the environment setup directly in a Yocto
    build::

       $ source tmp/deploy/images/qemux86-64/environment-setup-core2-64-poky-linux

 3. *Create the Makefile:* For this example, the Makefile contains
    two lines that can be used to set the :term:`CC` variable. One line is
    identical to the value that is set when you run the SDK environment
    setup script, and the other line sets :term:`CC` to "gcc", the default
    GNU compiler on the build host::

       # CC=i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
       # CC="gcc"
       all: main.o module.o
       	${CC} main.o module.o -o target_bin
       main.o: main.c module.h
       	${CC} -I . -c main.c
       module.o: module.c
       	module.h ${CC} -I . -c module.c
       clean:
       	rm -rf *.o
       	rm target_bin

 4. *Make the Project:* Use the ``make`` command to create the binary
    output file. Because variables are commented out in the Makefile, the
    value used for :term:`CC` is the value set when the SDK environment setup
    file was run::

       $ make
       i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
       i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
       i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin

    From the results of the previous command, you can see that
    the compiler used was the compiler established through the :term:`CC`
    variable defined in the setup script.

    You can override the :term:`CC` environment variable with the same
    variable as set from the Makefile by uncommenting the line in the
    Makefile and running ``make`` again.
    ::

       $ make clean
       rm -rf *.o
       rm target_bin
       #
       # Edit the Makefile by uncommenting the line that sets CC to "gcc"
       #
       $ make
       gcc -I . -c main.c
       gcc -I . -c module.c
       gcc main.o module.o -o target_bin

    As shown in the previous example, the
    cross-toolchain compiler is not used. Rather, the default compiler is
    used.

    This next case shows how to override a variable by providing the
    variable as part of the command line. Go into the Makefile and
    re-insert the comment character so that running ``make`` uses the
    established SDK compiler. However, when you run ``make``, use a
    command-line argument to set :term:`CC` to "gcc"::

       $ make clean
       rm -rf *.o
       rm target_bin
       #
       # Edit the Makefile to comment out the line setting CC to "gcc"
       #
       $ make
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin
       $ make clean
       rm -rf *.o
       rm target_bin
       $ make CC="gcc"
       gcc -I . -c main.c
       gcc -I . -c module.c
       gcc main.o module.o -o target_bin

    In the previous case, the command-line argument overrides the SDK
    environment variable.

    In this last case, edit Makefile again to use the "gcc" compiler but
    then use the "-e" option on the ``make`` command line::

       $ make clean
       rm -rf *.o
       rm target_bin
       #
       # Edit the Makefile to use "gcc"
       #
       $ make
       gcc -I . -c main.c
       gcc -I . -c module.c
       gcc main.o module.o -o target_bin
       $ make clean
       rm -rf *.o
       rm target_bin
       $ make -e
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
       i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin

    In the previous case, the "-e" option forces ``make`` to
    use the SDK environment variables regardless of the values in the
    Makefile.

 5. *Execute Your Project:* To execute the project (i.e. ``target_bin``),
    use the following command::

       $ ./target_bin
       Hello World!

    .. note::

       If you used the cross-toolchain compiler to build
       target_bin
       and your build host differs in architecture from that of the
       target machine, you need to run your project on the target device.

    As expected, the project displays the "Hello World!" message.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	********************************
	Using the SDK Toolchain Directly
	********************************

	You can use the SDK toolchain directly with Makefile and Autotools-based
	projects.

	Autotools-Based Projects
	========================

	Once you have a suitable :ref:`sdk-manual/intro:the cross-development toolchain`
	installed, it is very easy to develop a project using the `GNU
	Autotools-based <https://en.wikipedia.org/wiki/GNU_Build_System>`__
	workflow, which is outside of the :term:`OpenEmbedded Build System`.

	The following figure presents a simple Autotools workflow.

	.. image:: figures/sdk-autotools-flow.png
	:align: center
	:width: 70%

	Follow these steps to create a simple Autotools-based "Hello World"
	project:

	.. note::

	For more information on the GNU Autotools workflow, see the same
	example on the
	GNOME Developer
	site.

	1. Create a Working Directory and Populate It: Create a clean
	directory for your project and then make that directory your working
	location.
	::

	$ mkdir $HOME/helloworld
	$ cd $HOME/helloworld

	After setting up the directory, populate it with files needed for the flow.
	You need a project source file, a file to help with configuration,
	and a file to help create the Makefile, and a README file:
	``hello.c``, ``configure.ac``, ``Makefile.am``, and ``README``,
	respectively.

	Use the following command to create an empty README file, which is
	required by GNU Coding Standards::

	$ touch README

	Create the remaining
	three files as follows:

	- ``hello.c``::

	#include <stdio.h>

	main()
	{
	printf("Hello World!\n");
	}

	- ``configure.ac``::

	AC_INIT(hello,0.1)
	AM_INIT_AUTOMAKE([foreign])
	AC_PROG_CC
	AC_CONFIG_FILES(Makefile)
	AC_OUTPUT

	- ``Makefile.am``::

	bin_PROGRAMS = hello
	hello_SOURCES = hello.c

	2. Source the Cross-Toolchain Environment Setup File: As described
	earlier in the manual, installing the cross-toolchain creates a
	cross-toolchain environment setup script in the directory that the
	SDK was installed. Before you can use the tools to develop your
	project, you must source this setup script. The script begins with
	the string "environment-setup" and contains the machine architecture,
	which is followed by the string "poky-linux". For this example, the
	command sources a script from the default SDK installation directory
	that uses the 32-bit Intel x86 Architecture and the &DISTRO; Yocto
	Project release::

	$ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux

	Another example is sourcing the environment setup directly in a Yocto
	build::

	$ source tmp/deploy/images/qemux86-64/environment-setup-core2-64-poky-linux

	3. Create the configure Script: Use the ``autoreconf`` command to
	generate the ``configure`` script::

	$ autoreconf

	The ``autoreconf``
	tool takes care of running the other Autotools such as ``aclocal``,
	``autoconf``, and ``automake``.

	.. note::

	If you get errors from ``configure.ac``, which ``autoreconf``
	runs, that indicate missing files, you can use the "-i" option,
	which ensures missing auxiliary files are copied to the build
	host.

	4. Cross-Compile the Project: This command compiles the project using
	the cross-compiler. The
	:term:`CONFIGURE_FLAGS`
	environment variable provides the minimal arguments for GNU
	configure::

	$ ./configure ${CONFIGURE_FLAGS}

	For an Autotools-based
	project, you can use the cross-toolchain by just passing the
	appropriate host option to ``configure.sh``. The host option you use
	is derived from the name of the environment setup script found in the
	directory in which you installed the cross-toolchain. For example,
	the host option for an ARM-based target that uses the GNU EABI is
	``armv5te-poky-linux-gnueabi``. You will notice that the name of the
	script is ``environment-setup-armv5te-poky-linux-gnueabi``. Thus, the
	following command works to update your project and rebuild it using
	the appropriate cross-toolchain tools::

	$ ./configure --host=armv5te-poky-linux-gnueabi --with-libtool-sysroot=sysroot_dir

	5. Make and Install the Project: These two commands generate and
	install the project into the destination directory::

	$ make
	$ make install DESTDIR=./tmp

	.. note::

	To learn about environment variables established when you run the
	cross-toolchain environment setup script and how they are used or
	overridden by the Makefile, see the
	:ref:`sdk-manual/working-projects:makefile-based projects` section.

	This next command is a simple way to verify the installation of your
	project. Running the command prints the architecture on which the
	binary file can run. This architecture should be the same
	architecture that the installed cross-toolchain supports.
	::

	$ file ./tmp/usr/local/bin/hello

	6. Execute Your Project: To execute the project, you would need to run
	it on your target hardware. If your target hardware happens to be
	your build host, you could run the project as follows::

	$ ./tmp/usr/local/bin/hello

	As expected, the project displays the "Hello World!" message.

	Makefile-Based Projects
	=======================

	Simple Makefile-based projects use and interact with the cross-toolchain
	environment variables established when you run the cross-toolchain
	environment setup script. The environment variables are subject to
	general ``make`` rules.

	This section presents a simple Makefile development flow and provides an
	example that lets you see how you can use cross-toolchain environment
	variables and Makefile variables during development.

	.. image:: figures/sdk-makefile-flow.png
	:align: center
	:width: 70%

	The main point of this section is to explain the following three cases
	regarding variable behavior:

	- *Case 1 --- No Variables Set in the Makefile Map to Equivalent
	Environment Variables Set in the SDK Setup Script:* Because matching
	variables are not specifically set in the ``Makefile``, the variables
	retain their values based on the environment setup script.

	- *Case 2 --- Variables Are Set in the Makefile that Map to Equivalent
	Environment Variables from the SDK Setup Script:* Specifically
	setting matching variables in the ``Makefile`` during the build
	results in the environment settings of the variables being
	overwritten. In this case, the variables you set in the ``Makefile``
	are used.

	- *Case 3 --- Variables Are Set Using the Command Line that Map to
	Equivalent Environment Variables from the SDK Setup Script:*
	Executing the ``Makefile`` from the command line results in the
	environment variables being overwritten. In this case, the
	command-line content is used.

	.. note::

	Regardless of how you set your variables, if you use the "-e" option
	with ``make``, the variables from the SDK setup script take precedence::

	$ make -e target


	The remainder of this section presents a simple Makefile example that
	demonstrates these variable behaviors.

	In a new shell environment variables are not established for the SDK
	until you run the setup script. For example, the following commands show
	a null value for the compiler variable (i.e.
	:term:`CC`).
	::

	$ echo ${CC}

	$

	Running the
	SDK setup script for a 64-bit build host and an i586-tuned target
	architecture for a ``core-image-sato`` image using the current &DISTRO;
	Yocto Project release and then echoing that variable shows the value
	established through the script::

	$ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux
	$ echo ${CC}
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux

	To illustrate variable use, work through this simple "Hello World!"
	example:

	1. Create a Working Directory and Populate It: Create a clean
	directory for your project and then make that directory your working
	location.
	::

	$ mkdir $HOME/helloworld
	$ cd $HOME/helloworld

	After
	setting up the directory, populate it with files needed for the flow.
	You need a ``main.c`` file from which you call your function, a
	``module.h`` file to contain headers, and a ``module.c`` that defines
	your function.

	Create the three files as follows:

	- ``main.c``::

	#include "module.h"
	void sample_func();
	int main()
	{
	sample_func();
	return 0;
	}

	- ``module.h``::

	#include <stdio.h>
	void sample_func();

	- ``module.c``::

	#include "module.h"
	void sample_func()
	{
	printf("Hello World!");
	printf("\n");
	}

	2. Source the Cross-Toolchain Environment Setup File: As described
	earlier in the manual, installing the cross-toolchain creates a
	cross-toolchain environment setup script in the directory that the
	SDK was installed. Before you can use the tools to develop your
	project, you must source this setup script. The script begins with
	the string "environment-setup" and contains the machine architecture,
	which is followed by the string "poky-linux". For this example, the
	command sources a script from the default SDK installation directory
	that uses the 32-bit Intel x86 Architecture and the &DISTRO_NAME; Yocto
	Project release::

	$ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux

	Another example is sourcing the environment setup directly in a Yocto
	build::

	$ source tmp/deploy/images/qemux86-64/environment-setup-core2-64-poky-linux

	3. Create the Makefile: For this example, the Makefile contains
	two lines that can be used to set the :term:`CC` variable. One line is
	identical to the value that is set when you run the SDK environment
	setup script, and the other line sets :term:`CC` to "gcc", the default
	GNU compiler on the build host::

	# CC=i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
	# CC="gcc"
	all: main.o module.o
	${CC} main.o module.o -o target_bin
	main.o: main.c module.h
	${CC} -I . -c main.c
	module.o: module.c
	module.h ${CC} -I . -c module.c
	clean:
	rm -rf *.o
	rm target_bin

	4. Make the Project: Use the ``make`` command to create the binary
	output file. Because variables are commented out in the Makefile, the
	value used for :term:`CC` is the value set when the SDK environment setup
	file was run::

	$ make
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin

	From the results of the previous command, you can see that
	the compiler used was the compiler established through the :term:`CC`
	variable defined in the setup script.

	You can override the :term:`CC` environment variable with the same
	variable as set from the Makefile by uncommenting the line in the
	Makefile and running ``make`` again.
	::

	$ make clean
	rm -rf *.o
	rm target_bin
	#
	# Edit the Makefile by uncommenting the line that sets CC to "gcc"
	#
	$ make
	gcc -I . -c main.c
	gcc -I . -c module.c
	gcc main.o module.o -o target_bin

	As shown in the previous example, the
	cross-toolchain compiler is not used. Rather, the default compiler is
	used.

	This next case shows how to override a variable by providing the
	variable as part of the command line. Go into the Makefile and
	re-insert the comment character so that running ``make`` uses the
	established SDK compiler. However, when you run ``make``, use a
	command-line argument to set :term:`CC` to "gcc"::

	$ make clean
	rm -rf *.o
	rm target_bin
	#
	# Edit the Makefile to comment out the line setting CC to "gcc"
	#
	$ make
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin
	$ make clean
	rm -rf *.o
	rm target_bin
	$ make CC="gcc"
	gcc -I . -c main.c
	gcc -I . -c module.c
	gcc main.o module.o -o target_bin

	In the previous case, the command-line argument overrides the SDK
	environment variable.

	In this last case, edit Makefile again to use the "gcc" compiler but
	then use the "-e" option on the ``make`` command line::

	$ make clean
	rm -rf *.o
	rm target_bin
	#
	# Edit the Makefile to use "gcc"
	#
	$ make
	gcc -I . -c main.c
	gcc -I . -c module.c
	gcc main.o module.o -o target_bin
	$ make clean
	rm -rf *.o
	rm target_bin
	$ make -e
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c main.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux -I . -c module.c
	i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux main.o module.o -o target_bin

	In the previous case, the "-e" option forces ``make`` to
	use the SDK environment variables regardless of the values in the
	Makefile.

	5. Execute Your Project: To execute the project (i.e. ``target_bin``),
	use the following command::

	$ ./target_bin
	Hello World!

	.. note::

	If you used the cross-toolchain compiler to build
	target_bin
	and your build host differs in architecture from that of the
	target machine, you need to run your project on the target device.

	As expected, the project displays the "Hello World!" message.