This is the simplest but also least useful way to build packages for yocto. By default, there is no toolchain installed in the image.

To add the toolchain to an image, append tools-sdk to CORE_IMAGE_INSTALL.

CORE_IMAGE_INSTALL_append  = " tools-sdk"

Note that this will significantly increase image size and build time.

The most common way is to cross compile rather than compiling natively. Yocto provides an SDK package that can be built for an image to match possible dependencies in the image.

run this command to generate a cross development SDK:

bitbake <image name> -c populate_sdk
# for example:
bitbake ost-image -c populate_sdk

This will generate a toolchain with a sysroot containing all header/libraries/… included in the image. By default the SDK is in build/tmp/deploy/sdk/.

The sdk can be built as described above or can be fetched from Linux Images. Building the SDK will generate a few files. The most important one being a .sh script that is used to install the SDK. For example, building the SDK yields:

poky-glibc-x86_64-ost-image-dev-armv7at2hf-neon-bblue-toolchain-3.0.2.host.manifest
poky-glibc-x86_64-ost-image-dev-armv7at2hf-neon-bblue-toolchain-3.0.2.sh
poky-glibc-x86_64-ost-image-dev-armv7at2hf-neon-bblue-toolchain-3.0.2.target.manifest
poky-glibc-x86_64-ost-image-dev-armv7at2hf-neon-bblue-toolchain-3.0.2.testdata.json

Note that the file names include information about the image and hardware it was built for.

Installing the SDK is as simple as executing the shell script (e.g. poky-glibc-x86_64-ntb-dev-image-armv7at2hf-neon-bblue-toolchain-3.0.2.sh) and following the instructions. An example installation is shown below.

./tmp/deploy/sdk/poky-glibc-x86_64-ost-image-dev-armv7at2hf-neon-bblue-toolchain-3.0.2.sh
Poky (Yocto Project Reference Distro) SDK installer version 3.0.2
=================================================================
Enter target directory for SDK (default: /opt/poky/3.0.2):
You are about to install the SDK to "/opt/poky/3.0.2". Proceed [Y/n]? y
Extracting SDK.......................................................................................done
Setting it up...done
SDK has been successfully set up and is ready to be used.
Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
 $ . /opt/poky/3.0.2/environment-setup-armv7at2hf-neon-poky-linux-gnueabi

There are two things of note: The script will ask for a location to install the SDK to in case you do not want to install it to its default location. Also the last line of output will tell you what script needs to be sourced in order to use the SDK (see below).

The SDK includes a script that needs to be sourced in order to use the SDK. This, among other things, sets up the standard environment variables (such as CC, LD and CFLAGS).

The script is located in the SDK install directory and the install script tells you where to find it.

For the example above, the command is:

. /opt/poky/3.0.2/environment-setup-armv7at2hf-neon-poky-linux-gnueabi

Note the space between . and the path. The script needs to be sourced rather than executed. Now running any standard build system (eg make) should pick up the cross compile settings and automatically build for the target platform.

Live Coding with Yocto Project #4: SDKs