.. 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

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

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

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");
}

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