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| author | Richard Purdie <richard.purdie@linuxfoundation.org> | 2025-11-07 13:31:53 +0000 |
|---|---|---|
| committer | Richard Purdie <richard.purdie@linuxfoundation.org> | 2025-11-07 13:31:53 +0000 |
| commit | 8c22ff0d8b70d9b12f0487ef696a7e915b9e3173 (patch) | |
| tree | efdc32587159d0050a69009bdf2330a531727d95 /documentation/sdk-manual/intro.rst | |
| parent | d412d2747595c1cc4a5e3ca975e3adc31b2f7891 (diff) | |
| download | poky-8c22ff0d8b70d9b12f0487ef696a7e915b9e3173.tar.gz | |
The poky repository master branch is no longer being updated.
You can either:
a) switch to individual clones of bitbake, openembedded-core, meta-yocto and yocto-docs
b) use the new bitbake-setup
You can find information about either approach in our documentation:
https://docs.yoctoproject.org/
Note that "poky" the distro setting is still available in meta-yocto as
before and we continue to use and maintain that.
Long live Poky!
Some further information on the background of this change can be found
in: https://lists.openembedded.org/g/openembedded-architecture/message/2179
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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| 1 | .. SPDX-License-Identifier: CC-BY-SA-2.0-UK | ||
| 2 | |||
| 3 | ************ | ||
| 4 | Introduction | ||
| 5 | ************ | ||
| 6 | |||
| 7 | eSDK Introduction | ||
| 8 | ================= | ||
| 9 | |||
| 10 | Welcome to the Yocto Project Application Development and the Extensible | ||
| 11 | Software Development Kit (eSDK) manual. This manual | ||
| 12 | explains how to use both the Yocto Project extensible and standard | ||
| 13 | SDKs to develop applications and images. | ||
| 14 | |||
| 15 | All SDKs consist of the following: | ||
| 16 | |||
| 17 | - *Cross-Development Toolchain*: This toolchain contains a compiler, | ||
| 18 | debugger, and various associated tools. | ||
| 19 | |||
| 20 | - *Libraries, Headers, and Symbols*: The libraries, headers, and | ||
| 21 | symbols are specific to the image (i.e. they match the image | ||
| 22 | against which the SDK was built). | ||
| 23 | |||
| 24 | - *Environment Setup Script*: This ``*.sh`` file, once sourced, sets up the | ||
| 25 | cross-development environment by defining variables and preparing for | ||
| 26 | SDK use. | ||
| 27 | |||
| 28 | Additionally, an extensible SDK has tools that allow you to easily add | ||
| 29 | new applications and libraries to an image, modify the source of an | ||
| 30 | existing component, test changes on the target hardware, and easily | ||
| 31 | integrate an application into the :term:`OpenEmbedded Build System`. | ||
| 32 | |||
| 33 | You can use an SDK to independently develop and test code that is | ||
| 34 | destined to run on some target machine. SDKs are completely | ||
| 35 | self-contained. The binaries are linked against their own copy of | ||
| 36 | ``libc``, which results in no dependencies on the target system. To | ||
| 37 | achieve this, the pointer to the dynamic loader is configured at install | ||
| 38 | time since that path cannot be dynamically altered. This is the reason | ||
| 39 | for a wrapper around the ``populate_sdk`` and ``populate_sdk_ext`` | ||
| 40 | archives. | ||
| 41 | |||
| 42 | Another feature of the SDKs is that only one set of cross-compiler | ||
| 43 | toolchain binaries are produced for any given architecture. This feature | ||
| 44 | takes advantage of the fact that the target hardware can be passed to | ||
| 45 | ``gcc`` as a set of compiler options. Those options are set up by the | ||
| 46 | environment script and contained in variables such as | ||
| 47 | :term:`CC` and | ||
| 48 | :term:`LD`. This reduces the space needed | ||
| 49 | for the tools. Understand, however, that every target still needs its own | ||
| 50 | sysroot because those binaries are target-specific. | ||
| 51 | |||
| 52 | The SDK development environment consists of the following: | ||
| 53 | |||
| 54 | - The self-contained SDK, which is an architecture-specific | ||
| 55 | cross-toolchain and matching sysroots (target and native) all built | ||
| 56 | by the OpenEmbedded build system (e.g. the SDK). The toolchain and | ||
| 57 | sysroots are based on a :term:`Metadata` | ||
| 58 | configuration and extensions, which allows you to cross-develop on | ||
| 59 | the host machine for the target hardware. Additionally, the | ||
| 60 | extensible SDK contains the ``devtool`` functionality. | ||
| 61 | |||
| 62 | - The Quick EMUlator (QEMU), which lets you simulate target hardware. | ||
| 63 | QEMU is not literally part of the SDK. You must build and include | ||
| 64 | this emulator separately. However, QEMU plays an important role in | ||
| 65 | the development process that revolves around use of the SDK. | ||
| 66 | |||
| 67 | In summary, the extensible and standard SDK share many features. | ||
| 68 | However, the extensible SDK has powerful development tools to help you | ||
| 69 | more quickly develop applications. Here is a table that summarizes | ||
| 70 | the primary differences between the standard and extensible SDK types | ||
| 71 | when considering which to build: | ||
| 72 | |||
| 73 | +-----------------------+-----------------------+-----------------------+ | ||
| 74 | | *Feature* | *Standard SDK* | *Extensible SDK* | | ||
| 75 | +=======================+=======================+=======================+ | ||
| 76 | | Toolchain | Yes | Yes [1]_ | | ||
| 77 | +-----------------------+-----------------------+-----------------------+ | ||
| 78 | | Debugger | Yes | Yes [1]_ | | ||
| 79 | +-----------------------+-----------------------+-----------------------+ | ||
| 80 | | Size | 100+ MBytes | 1+ GBytes (or 300+ | | ||
| 81 | | | | MBytes for minimal | | ||
| 82 | | | | w/toolchain) | | ||
| 83 | +-----------------------+-----------------------+-----------------------+ | ||
| 84 | | ``devtool`` | No | Yes | | ||
| 85 | +-----------------------+-----------------------+-----------------------+ | ||
| 86 | | Build Images | No | Yes | | ||
| 87 | +-----------------------+-----------------------+-----------------------+ | ||
| 88 | | Updateable | No | Yes | | ||
| 89 | +-----------------------+-----------------------+-----------------------+ | ||
| 90 | | Managed Sysroot [2]_ | No | Yes | | ||
| 91 | +-----------------------+-----------------------+-----------------------+ | ||
| 92 | | Installed Packages | No [3]_ | Yes [4]_ | | ||
| 93 | +-----------------------+-----------------------+-----------------------+ | ||
| 94 | | Construction | Packages | Shared State | | ||
| 95 | +-----------------------+-----------------------+-----------------------+ | ||
| 96 | |||
| 97 | .. [1] Extensible SDK contains the toolchain and debugger if :term:`SDK_EXT_TYPE` | ||
| 98 | is "full" or :term:`SDK_INCLUDE_TOOLCHAIN` is "1", which is the default. | ||
| 99 | .. [2] Sysroot is managed through the use of ``devtool``. Thus, it is less | ||
| 100 | likely that you will corrupt your SDK sysroot when you try to add | ||
| 101 | additional libraries. | ||
| 102 | .. [3] You can add runtime package management to the standard SDK but it is not | ||
| 103 | supported by default. | ||
| 104 | .. [4] You must build and make the shared state available to extensible SDK | ||
| 105 | users for "packages" you want to enable users to install. | ||
| 106 | |||
| 107 | The Cross-Development Toolchain | ||
| 108 | ------------------------------- | ||
| 109 | |||
| 110 | The :term:`Cross-Development Toolchain` consists | ||
| 111 | of a cross-compiler, cross-linker, and cross-debugger that are used to | ||
| 112 | develop user-space applications for targeted hardware; in addition, | ||
| 113 | the extensible SDK comes with built-in ``devtool`` | ||
| 114 | functionality. This toolchain is created by running a SDK installer | ||
| 115 | script or through a :term:`Build Directory` that is based on | ||
| 116 | your metadata configuration or extension for your targeted device. The | ||
| 117 | cross-toolchain works with a matching target sysroot. | ||
| 118 | |||
| 119 | Sysroots | ||
| 120 | -------- | ||
| 121 | |||
| 122 | The native and target sysroots contain needed headers and libraries for | ||
| 123 | generating binaries that run on the target architecture. The target | ||
| 124 | sysroot is based on the target root filesystem image that is built by | ||
| 125 | the OpenEmbedded build system and uses the same metadata configuration | ||
| 126 | used to build the cross-toolchain. | ||
| 127 | |||
| 128 | The QEMU Emulator | ||
| 129 | ----------------- | ||
| 130 | |||
| 131 | The QEMU emulator allows you to simulate your hardware while running | ||
| 132 | your application or image. QEMU is not part of the SDK but is | ||
| 133 | automatically installed and available if you have done any one of | ||
| 134 | the following: | ||
| 135 | |||
| 136 | - cloned the ``poky`` Git repository to create a | ||
| 137 | :term:`Source Directory` and sourced the environment setup script. | ||
| 138 | |||
| 139 | - downloaded a Yocto Project release and unpacked it to | ||
| 140 | create a Source Directory and sourced the environment setup | ||
| 141 | script. | ||
| 142 | |||
| 143 | - installed the cross-toolchain tarball and | ||
| 144 | sourced the toolchain's setup environment script. | ||
| 145 | |||
| 146 | SDK Development Model | ||
| 147 | ===================== | ||
| 148 | |||
| 149 | Fundamentally, the SDK fits into the development process as follows: | ||
| 150 | |||
| 151 | .. image:: figures/sdk-environment.png | ||
| 152 | :width: 100% | ||
| 153 | |||
| 154 | The SDK is installed on any machine and can be used to develop applications, | ||
| 155 | images, and kernels. An SDK can even be used by a QA Engineer or Release | ||
| 156 | Engineer. The fundamental concept is that the machine that has the SDK | ||
| 157 | installed does not have to be associated with the machine that has the | ||
| 158 | Yocto Project installed. A developer can independently compile and test | ||
| 159 | an object on their machine and then, when the object is ready for | ||
| 160 | integration into an image, they can simply make it available to the | ||
| 161 | machine that has the Yocto Project. Once the object is available, the | ||
| 162 | image can be rebuilt using the Yocto Project to produce the modified | ||
| 163 | image. | ||
| 164 | |||
| 165 | You just need to follow these general steps: | ||
| 166 | |||
| 167 | #. *Install the SDK for your target hardware:* For information on how to | ||
| 168 | install the SDK, see the ":ref:`sdk-manual/using:installing the sdk`" | ||
| 169 | section. | ||
| 170 | |||
| 171 | #. *Download or Build the Target Image:* The Yocto Project supports | ||
| 172 | several target architectures and has many pre-built kernel images and | ||
| 173 | root filesystem images. | ||
| 174 | |||
| 175 | If you are going to develop your application on hardware, go to the | ||
| 176 | :yocto_dl:`machines </releases/yocto/&DISTRO_REL_LATEST_TAG;/machines/>` download area and choose a | ||
| 177 | target machine area from which to download the kernel image and root | ||
| 178 | filesystem. This download area could have several files in it that | ||
| 179 | support development using actual hardware. For example, the area | ||
| 180 | might contain ``.hddimg`` files that combine the kernel image with | ||
| 181 | the filesystem, boot loaders, and so forth. Be sure to get the files | ||
| 182 | you need for your particular development process. | ||
| 183 | |||
| 184 | If you are going to develop your application and then run and test it | ||
| 185 | using the QEMU emulator, go to the | ||
| 186 | :yocto_dl:`machines/qemu </releases/yocto/&DISTRO_REL_LATEST_TAG;/machines/qemu>` download area. From this | ||
| 187 | area, go down into the directory for your target architecture (e.g. | ||
| 188 | ``qemux86_64`` for an Intel-based 64-bit architecture). Download the | ||
| 189 | kernel, root filesystem, and any other files you need for your | ||
| 190 | process. | ||
| 191 | |||
| 192 | .. note:: | ||
| 193 | |||
| 194 | To use the root filesystem in QEMU, you need to extract it. See the | ||
| 195 | ":ref:`sdk-manual/appendix-obtain:extracting the root filesystem`" | ||
| 196 | section for information on how to do this extraction. | ||
| 197 | |||
| 198 | #. *Develop and Test your Application:* At this point, you have the | ||
| 199 | tools to develop your application. If you need to separately install | ||
| 200 | and use the QEMU emulator, you can go to `QEMU Home | ||
| 201 | Page <https://wiki.qemu.org/Main_Page>`__ to download and learn about | ||
| 202 | the emulator. See the ":doc:`/dev-manual/qemu`" chapter in the | ||
| 203 | Yocto Project Development Tasks Manual for information on using QEMU | ||
| 204 | within the Yocto Project. | ||
| 205 | |||
| 206 | The remainder of this manual describes how to use the extensible and | ||
| 207 | standard SDKs. There is also information in appendix form describing | ||
| 208 | how you can build, install, and modify an SDK. | ||
