poky/documentation/sdk-manual/intro.rst - mdmillerii/openbmc - Gitiles

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

 ************
 Introduction
 ************

 eSDK Introduction
 =================

 Welcome to the Yocto Project Application Development and the Extensible
 Software Development Kit (eSDK) manual. This manual
 explains how to use both the Yocto Project extensible and standard
 SDKs to develop applications and images.

 All SDKs consist of the following:

 -  *Cross-Development Toolchain*: This toolchain contains a compiler,
    debugger, and various associated tools.

 -  *Libraries, Headers, and Symbols*: The libraries, headers, and
    symbols are specific to the image (i.e. they match the image
    against which the SDK was built).

 -  *Environment Setup Script*: This ``*.sh`` file, once sourced, sets up the
    cross-development environment by defining variables and preparing for
    SDK use.

 Additionally, an extensible SDK has tools that allow you to easily add
 new applications and libraries to an image, modify the source of an
 existing component, test changes on the target hardware, and easily
 integrate an application into the :term:`OpenEmbedded Build System`.

 You can use an SDK to independently develop and test code that is
 destined to run on some target machine. SDKs are completely
 self-contained. The binaries are linked against their own copy of
 ``libc``, which results in no dependencies on the target system. To
 achieve this, the pointer to the dynamic loader is configured at install
 time since that path cannot be dynamically altered. This is the reason
 for a wrapper around the ``populate_sdk`` and ``populate_sdk_ext``
 archives.

 Another feature of the SDKs is that only one set of cross-compiler
 toolchain binaries are produced for any given architecture. This feature
 takes advantage of the fact that the target hardware can be passed to
 ``gcc`` as a set of compiler options. Those options are set up by the
 environment script and contained in variables such as
 :term:`CC` and
 :term:`LD`. This reduces the space needed
 for the tools. Understand, however, that every target still needs its own
 sysroot because those binaries are target-specific.

 The SDK development environment consists of the following:

 -  The self-contained SDK, which is an architecture-specific
    cross-toolchain and matching sysroots (target and native) all built
    by the OpenEmbedded build system (e.g. the SDK). The toolchain and
    sysroots are based on a :term:`Metadata`
    configuration and extensions, which allows you to cross-develop on
    the host machine for the target hardware. Additionally, the
    extensible SDK contains the ``devtool`` functionality.

 -  The Quick EMUlator (QEMU), which lets you simulate target hardware.
    QEMU is not literally part of the SDK. You must build and include
    this emulator separately. However, QEMU plays an important role in
    the development process that revolves around use of the SDK.

 In summary, the extensible and standard SDK share many features.
 However, the extensible SDK has powerful development tools to help you
 more quickly develop applications. Following is a table that summarizes
 the primary differences between the standard and extensible SDK types
 when considering which to build:

 +-----------------------+-----------------------+-----------------------+
 | *Feature*             | *Standard SDK*        | *Extensible SDK*      |
 +=======================+=======================+=======================+
 | Toolchain             | Yes                   | Yes [1]_              |
 +-----------------------+-----------------------+-----------------------+
 | Debugger              | Yes                   | Yes [1]_              |
 +-----------------------+-----------------------+-----------------------+
 | Size                  | 100+ MBytes           | 1+ GBytes (or 300+    |
 |                       |                       | MBytes for minimal    |
 |                       |                       | w/toolchain)          |
 +-----------------------+-----------------------+-----------------------+
 | ``devtool``           | No                    | Yes                   |
 +-----------------------+-----------------------+-----------------------+
 | Build Images          | No                    | Yes                   |
 +-----------------------+-----------------------+-----------------------+
 | Updateable            | No                    | Yes                   |
 +-----------------------+-----------------------+-----------------------+
 | Managed Sysroot [2]_  | No                    | Yes                   |
 +-----------------------+-----------------------+-----------------------+
 | Installed Packages    | No  [3]_              | Yes  [4]_             |
 +-----------------------+-----------------------+-----------------------+
 | Construction          | Packages              | Shared State          |
 +-----------------------+-----------------------+-----------------------+

 .. [1] Extensible SDK contains the toolchain and debugger if :term:`SDK_EXT_TYPE`
        is "full" or :term:`SDK_INCLUDE_TOOLCHAIN` is "1", which is the default.
 .. [2] Sysroot is managed through the use of ``devtool``. Thus, it is less
        likely that you will corrupt your SDK sysroot when you try to add
        additional libraries.
 .. [3] You can add runtime package management to the standard SDK but it is not
        supported by default.
 .. [4] You must build and make the shared state available to extensible SDK
        users for "packages" you want to enable users to install.

 The Cross-Development Toolchain
 -------------------------------

 The :term:`Cross-Development Toolchain` consists
 of a cross-compiler, cross-linker, and cross-debugger that are used to
 develop user-space applications for targeted hardware; in addition,
 the extensible SDK comes with built-in ``devtool``
 functionality. This toolchain is created by running a SDK installer
 script or through a :term:`Build Directory` that is based on
 your metadata configuration or extension for your targeted device. The
 cross-toolchain works with a matching target sysroot.

 Sysroots
 --------

 The native and target sysroots contain needed headers and libraries for
 generating binaries that run on the target architecture. The target
 sysroot is based on the target root filesystem image that is built by
 the OpenEmbedded build system and uses the same metadata configuration
 used to build the cross-toolchain.

 The QEMU Emulator
 -----------------

 The QEMU emulator allows you to simulate your hardware while running
 your application or image. QEMU is not part of the SDK but is
 automatically installed and available if you have done any one of
 the following:

 -  cloned the ``poky`` Git repository to create a
    :term:`Source Directory` and sourced the environment setup script.

 -  downloaded a Yocto Project release and unpacked it to
    create a Source Directory and sourced the environment setup
    script.

 -  installed the cross-toolchain tarball and
    sourced the toolchain's setup environment script.

 SDK Development Model
 =====================

 Fundamentally, the SDK fits into the development process as follows:

 .. image:: figures/sdk-environment.png
    :width: 100%

 The SDK is installed on any machine and can be used to develop applications,
 images, and kernels. An SDK can even be used by a QA Engineer or Release
 Engineer. The fundamental concept is that the machine that has the SDK
 installed does not have to be associated with the machine that has the
 Yocto Project installed. A developer can independently compile and test
 an object on their machine and then, when the object is ready for
 integration into an image, they can simply make it available to the
 machine that has the Yocto Project. Once the object is available, the
 image can be rebuilt using the Yocto Project to produce the modified
 image.

 You just need to follow these general steps:

 1. *Install the SDK for your target hardware:* For information on how to
    install the SDK, see the ":ref:`sdk-manual/using:installing the sdk`"
    section.

 2. *Download or Build the Target Image:* The Yocto Project supports
    several target architectures and has many pre-built kernel images and
    root filesystem images.

    If you are going to develop your application on hardware, go to the
    :yocto_dl:`machines </releases/yocto/yocto-&DISTRO;/machines/>` download area and choose a
    target machine area from which to download the kernel image and root
    filesystem. This download area could have several files in it that
    support development using actual hardware. For example, the area
    might contain ``.hddimg`` files that combine the kernel image with
    the filesystem, boot loaders, and so forth. Be sure to get the files
    you need for your particular development process.

    If you are going to develop your application and then run and test it
    using the QEMU emulator, go to the
    :yocto_dl:`machines/qemu </releases/yocto/yocto-&DISTRO;/machines/qemu>` download area. From this
    area, go down into the directory for your target architecture (e.g.
    ``qemux86_64`` for an Intel-based 64-bit architecture). Download the
    kernel, root filesystem, and any other files you need for your
    process.

    .. note::

       To use the root filesystem in QEMU, you need to extract it. See the
       ":ref:`sdk-manual/appendix-obtain:extracting the root filesystem`"
       section for information on how to do this extraction.

 3. *Develop and Test your Application:* At this point, you have the
    tools to develop your application. If you need to separately install
    and use the QEMU emulator, you can go to `QEMU Home
    Page <https://wiki.qemu.org/Main_Page>`__ to download and learn about
    the emulator. See the ":doc:`/dev-manual/qemu`" chapter in the
    Yocto Project Development Tasks Manual for information on using QEMU
    within the Yocto Project.

 The remainder of this manual describes how to use the extensible and
 standard SDKs. There is also information in appendix form describing
 how you can build, install, and modify an SDK.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	************
	Introduction
	************

	eSDK Introduction
	=================

	Welcome to the Yocto Project Application Development and the Extensible
	Software Development Kit (eSDK) manual. This manual
	explains how to use both the Yocto Project extensible and standard
	SDKs to develop applications and images.

	All SDKs consist of the following:

	- Cross-Development Toolchain: This toolchain contains a compiler,
	debugger, and various associated tools.

	- Libraries, Headers, and Symbols: The libraries, headers, and
	symbols are specific to the image (i.e. they match the image
	against which the SDK was built).

	- Environment Setup Script: This ``*.sh`` file, once sourced, sets up the
	cross-development environment by defining variables and preparing for
	SDK use.

	Additionally, an extensible SDK has tools that allow you to easily add
	new applications and libraries to an image, modify the source of an
	existing component, test changes on the target hardware, and easily
	integrate an application into the :term:`OpenEmbedded Build System`.

	You can use an SDK to independently develop and test code that is
	destined to run on some target machine. SDKs are completely
	self-contained. The binaries are linked against their own copy of
	``libc``, which results in no dependencies on the target system. To
	achieve this, the pointer to the dynamic loader is configured at install
	time since that path cannot be dynamically altered. This is the reason
	for a wrapper around the ``populate_sdk`` and ``populate_sdk_ext``
	archives.

	Another feature of the SDKs is that only one set of cross-compiler
	toolchain binaries are produced for any given architecture. This feature
	takes advantage of the fact that the target hardware can be passed to
	``gcc`` as a set of compiler options. Those options are set up by the
	environment script and contained in variables such as
	:term:`CC` and
	:term:`LD`. This reduces the space needed
	for the tools. Understand, however, that every target still needs its own
	sysroot because those binaries are target-specific.

	The SDK development environment consists of the following:

	- The self-contained SDK, which is an architecture-specific
	cross-toolchain and matching sysroots (target and native) all built
	by the OpenEmbedded build system (e.g. the SDK). The toolchain and
	sysroots are based on a :term:`Metadata`
	configuration and extensions, which allows you to cross-develop on
	the host machine for the target hardware. Additionally, the
	extensible SDK contains the ``devtool`` functionality.

	- The Quick EMUlator (QEMU), which lets you simulate target hardware.
	QEMU is not literally part of the SDK. You must build and include
	this emulator separately. However, QEMU plays an important role in
	the development process that revolves around use of the SDK.

	In summary, the extensible and standard SDK share many features.
	However, the extensible SDK has powerful development tools to help you
	more quickly develop applications. Following is a table that summarizes
	the primary differences between the standard and extensible SDK types
	when considering which to build:

	+-----------------------+-----------------------+-----------------------+
	\| Feature \| Standard SDK \| Extensible SDK \|
	+=======================+=======================+=======================+
	\| Toolchain \| Yes \| Yes [1]_ \|
	+-----------------------+-----------------------+-----------------------+
	\| Debugger \| Yes \| Yes [1]_ \|
	+-----------------------+-----------------------+-----------------------+
	\| Size \| 100+ MBytes \| 1+ GBytes (or 300+ \|
	\| \| \| MBytes for minimal \|
	\| \| \| w/toolchain) \|
	+-----------------------+-----------------------+-----------------------+
	\| ``devtool`` \| No \| Yes \|
	+-----------------------+-----------------------+-----------------------+
	\| Build Images \| No \| Yes \|
	+-----------------------+-----------------------+-----------------------+
	\| Updateable \| No \| Yes \|
	+-----------------------+-----------------------+-----------------------+
	\| Managed Sysroot [2]_ \| No \| Yes \|
	+-----------------------+-----------------------+-----------------------+
	\| Installed Packages \| No [3]_ \| Yes [4]_ \|
	+-----------------------+-----------------------+-----------------------+
	\| Construction \| Packages \| Shared State \|
	+-----------------------+-----------------------+-----------------------+

	.. [1] Extensible SDK contains the toolchain and debugger if :term:`SDK_EXT_TYPE`
	is "full" or :term:`SDK_INCLUDE_TOOLCHAIN` is "1", which is the default.
	.. [2] Sysroot is managed through the use of ``devtool``. Thus, it is less
	likely that you will corrupt your SDK sysroot when you try to add
	additional libraries.
	.. [3] You can add runtime package management to the standard SDK but it is not
	supported by default.
	.. [4] You must build and make the shared state available to extensible SDK
	users for "packages" you want to enable users to install.

	The Cross-Development Toolchain
	-------------------------------

	The :term:`Cross-Development Toolchain` consists
	of a cross-compiler, cross-linker, and cross-debugger that are used to
	develop user-space applications for targeted hardware; in addition,
	the extensible SDK comes with built-in ``devtool``
	functionality. This toolchain is created by running a SDK installer
	script or through a :term:`Build Directory` that is based on
	your metadata configuration or extension for your targeted device. The
	cross-toolchain works with a matching target sysroot.

	Sysroots
	--------

	The native and target sysroots contain needed headers and libraries for
	generating binaries that run on the target architecture. The target
	sysroot is based on the target root filesystem image that is built by
	the OpenEmbedded build system and uses the same metadata configuration
	used to build the cross-toolchain.

	The QEMU Emulator
	-----------------

	The QEMU emulator allows you to simulate your hardware while running
	your application or image. QEMU is not part of the SDK but is
	automatically installed and available if you have done any one of
	the following:

	- cloned the ``poky`` Git repository to create a
	:term:`Source Directory` and sourced the environment setup script.

	- downloaded a Yocto Project release and unpacked it to
	create a Source Directory and sourced the environment setup
	script.

	- installed the cross-toolchain tarball and
	sourced the toolchain's setup environment script.

	SDK Development Model
	=====================

	Fundamentally, the SDK fits into the development process as follows:

	.. image:: figures/sdk-environment.png
	:width: 100%

	The SDK is installed on any machine and can be used to develop applications,
	images, and kernels. An SDK can even be used by a QA Engineer or Release
	Engineer. The fundamental concept is that the machine that has the SDK
	installed does not have to be associated with the machine that has the
	Yocto Project installed. A developer can independently compile and test
	an object on their machine and then, when the object is ready for
	integration into an image, they can simply make it available to the
	machine that has the Yocto Project. Once the object is available, the
	image can be rebuilt using the Yocto Project to produce the modified
	image.

	You just need to follow these general steps:

	1. Install the SDK for your target hardware: For information on how to
	install the SDK, see the ":ref:`sdk-manual/using:installing the sdk`"
	section.

	2. Download or Build the Target Image: The Yocto Project supports
	several target architectures and has many pre-built kernel images and
	root filesystem images.

	If you are going to develop your application on hardware, go to the
	:yocto_dl:`machines </releases/yocto/yocto-&DISTRO;/machines/>` download area and choose a
	target machine area from which to download the kernel image and root
	filesystem. This download area could have several files in it that
	support development using actual hardware. For example, the area
	might contain ``.hddimg`` files that combine the kernel image with
	the filesystem, boot loaders, and so forth. Be sure to get the files
	you need for your particular development process.

	If you are going to develop your application and then run and test it
	using the QEMU emulator, go to the
	:yocto_dl:`machines/qemu </releases/yocto/yocto-&DISTRO;/machines/qemu>` download area. From this
	area, go down into the directory for your target architecture (e.g.
	``qemux86_64`` for an Intel-based 64-bit architecture). Download the
	kernel, root filesystem, and any other files you need for your
	process.

	.. note::

	To use the root filesystem in QEMU, you need to extract it. See the
	":ref:`sdk-manual/appendix-obtain:extracting the root filesystem`"
	section for information on how to do this extraction.

	3. Develop and Test your Application: At this point, you have the
	tools to develop your application. If you need to separately install
	and use the QEMU emulator, you can go to `QEMU Home
	Page <https://wiki.qemu.org/Main_Page>`__ to download and learn about
	the emulator. See the ":doc:`/dev-manual/qemu`" chapter in the
	Yocto Project Development Tasks Manual for information on using QEMU
	within the Yocto Project.

	The remainder of this manual describes how to use the extensible and
	standard SDKs. There is also information in appendix form describing
	how you can build, install, and modify an SDK.