README.md
1# OpenCL<sup>TM</sup> ICD Loader
2
3This repo contains the source code and tests for the Khronos official OpenCL ICD Loader.
4
5## CI Build Status
6
7[](https://github.com/KhronosGroup/OpenCL-ICD-Loader/actions?query=workflow%3AWindows)
8[](https://github.com/KhronosGroup/OpenCL-ICD-Loader/actions?query=workflow%3ALinux)
9[](https://github.com/KhronosGroup/OpenCL-ICD-Loader/actions?query=workflow%3AMacOS)
10
11## Introduction
12
13OpenCL defines an *Installable Client Driver* (ICD) mechanism to allow developers to build applications against an *Installable Client Driver* loader (ICD loader) rather than linking their applications against a specific OpenCL implementation.
14The ICD Loader is responsible for:
15
16* Exporting OpenCL API entry points
17* Enumerating OpenCL implementations
18* Forwarding OpenCL API calls to the correct implementation
19
20This repo contains the source code and tests for the Khronos official OpenCL ICD Loader.
21
22Note that this repo does not contain an OpenCL implementation (ICD).
23You will need to obtain and install an OpenCL implementation for your OpenCL device that supports the OpenCL ICD extension `cl_khr_icd` to run an application using the OpenCL ICD Loader.
24
25The OpenCL *Installable Client Driver* extension (`cl_khr_icd`) is described in the OpenCL extensions specification, which may be found on the [Khronos OpenCL Registry](https://www.khronos.org/registry/OpenCL/).
26
27## Build Instructions
28
29> While the ICD Loader can be built and installed in isolation, it is part of the [OpenCL SDK](https://github.com/KhronosGroup/OpenCL-SDK). If looking for streamlined build experience and a complete development package, refer to the SDK build instructions instead of the following guide.
30
31### Dependencies
32
33The OpenCL ICD Loader requires:
34- the [OpenCL Headers](https://github.com/KhronosGroup/OpenCL-Headers/).
35 - It is recommended to install the headers via CMake, however a convenience shorthand is provided. Providing `OPENCL_ICD_LOADER_HEADERS_DIR` to CMake, one may specify the location of OpenCL Headers. By default, the OpenCL ICD Loader will look for OpenCL Headers in the inc directory.
36- The OpenCL ICD Loader uses CMake for its build system.
37If CMake is not provided by your build system or OS package manager, please consult the [CMake website](https://cmake.org).
38
39### Example Build
40
41For most Windows and Linux usages, the following steps are sufficient to build the OpenCL ICD Loader:
42
431. Clone this repo and the OpenCL Headers:
44
45 git clone https://github.com/KhronosGroup/OpenCL-ICD-Loader
46 git clone https://github.com/KhronosGroup/OpenCL-Headers
47
481. Install OpenCL Headers CMake package
49
50 cmake -D CMAKE_INSTALL_PREFIX=./OpenCL-Headers/install -S ./OpenCL-Headers -B ./OpenCL-Headers/build
51 cmake --build ./OpenCL-Headers/build --target install
52
531. Build and install OpenCL ICD Loader CMake package. _(Note that `CMAKE_PREFIX_PATH` need to be an absolute path. Update as needed.)_
54
55 cmake -D CMAKE_PREFIX_PATH=/absolute/path/to/OpenCL-Headers/install -D CMAKE_INSTALL_PREFIX=./OpenCL-ICD-Loader/install -S ./OpenCL-ICD-Loader -B ./OpenCL-ICD-Loader/build
56 cmake --build ./OpenCL-ICD-Loader/build --target install
57
58Notes:
59
60* For x64 Windows builds, you need to instruct the default Visual Studio generator by adding `-A x64` to all your command-lines.
61
62* Some users may prefer to use a CMake GUI frontend, such as `cmake-gui` or `ccmake`, vs. the command-line CMake.
63
64### Example Use
65
66Example CMake invocation
67
68```bash
69cmake -D CMAKE_PREFIX_PATH="/chosen/install/prefix/of/headers;/chosen/install/prefix/of/loader" /path/to/opencl/app
70```
71
72and sample `CMakeLists.txt`
73
74```cmake
75cmake_minimum_required(VERSION 3.0)
76cmake_policy(VERSION 3.0...3.18.4)
77project(proj)
78add_executable(app main.cpp)
79find_package(OpenCLHeaders REQUIRED)
80find_package(OpenCLICDLoader REQUIRED)
81target_link_libraries(app PRIVATE OpenCL::Headers OpenCL::OpenCL)
82```
83
84## OpenCL ICD Loader Tests
85
86OpenCL ICD Loader Tests can be run using `ctest` from the `build` directory. CTest which is a companion to CMake. The OpenCL ICD Loader Tests can also be run directly by executing `icd_loader_test[.exe]` executable from the bin folder.
87
88_(Note that running the tests manually requires setting up it's env manually, by setting `OCL_ICD_FILENAMES` to the full path of `libOpenCLDriverStub.so`/`OpenCLDriverStub.dll`, something otherwise done by CTest.)_
89
90## Registering ICDs
91
92The method to installing an ICD is operating system dependent.
93
94### Registering an ICD on Linux
95
96Install your ICD by creating a file with the full path to the library of your implementation in `/etc/OpenCL/vendors` for eg.:
97
98 echo full/path/to/libOpenCLDriverStub.so > /etc/OpenCL/vendors/test.icd
99
100### Registering an ICD on Windows
101
102Install your ICD by adding a `REG_DWORD` value to the registry keys:
103
104 // For 32-bit operating systems, or 64-bit tests on a 64-bit operating system:
105 HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenCL\Vendors
106
107 // For 32-bit tests on a 64-bit operating system:
108 HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Khronos\OpenCL\Vendors
109
110 // The name of the REG_DWORD value should be the full path to the library of your implementation, for eg.
111 // OpenCLDriverStub.dll, and the data for this value should be 0.
112
113## About Layers
114
115Layers have been added as an experimental feature in the OpenCL ICD Loader. We do not
116expect the API or ABI to change significantly, but the OpenCL Working Group reserves
117the right to do so. The layer support can also be completely deactivated during
118configuration by using the `ENABLE_OPENCL_LAYERS` (`ON` by default) cmake variable:
119
120```bash
121cmake -DENABLE_OPENCL_LAYERS=OFF
122```
123
124For now, runtime configuration of layers is done using the `OPENCL_LAYERS` environment
125variable. A colon (Linux) or semicolon (Windows) list of layers to use can be provided
126through this environment variable.
127
128We are looking for feedback.
129
130## Support
131
132Please create a GitHub issue to report an issue or ask questions.
133
134## Contributing
135
136Contributions to the OpenCL ICD Loader are welcomed and encouraged.
137You will be prompted with a one-time "click-through" CLA dialog as part of submitting your pull request or other contribution to GitHub.
138
139## Table of Debug Environment Variables
140
141The following debug environment variables are available for use with the OpenCL ICD loader:
142
143| Environment Variable | Behavior | Example Format |
144|:---------------------------------:|---------------------|----------------------|
145| OCL_ICD_FILENAMES | Specifies a list of additional ICDs to load. The ICDs will be enumerated first, before any ICDs discovered via default mechanisms. | `export OCL_ICD_FILENAMES=libVendorA.so:libVendorB.so`<br/><br/>`set OCL_ICD_FILENAMES=vendor_a.dll;vendor_b.dll` |
146| OCL_ICD_VENDORS | On Linux and Android, specifies a directory to scan for ICDs to enumerate in place of the default `/etc/OpenCL/vendors'. | `export OCL_ICD_VENDORS=/my/local/icd/search/path` |
147| OPENCL_LAYERS | Specifies a list of layers to load. | `export OPENCL_LAYERS=libLayerA.so:libLayerB.so`<br/><br/>`set OPENCL_LAYERS=libLayerA.dll;libLayerB.dll` |
148| OPENCL_LAYER_PATH | On Linux and Android, specifies a directory to scan for layers to enumerate in place of the default `/etc/OpenCL/layers'. | `export OPENCL_LAYER_PATH=/my/local/layers/search/path` |
149| OCL_ICD_ENABLE_TRACE | Enable the trace mechanism | `export OCL_ICD_ENABLE_TRACE=True`<br/><br/>`set OCL_ICD_ENABLE_TRACE=True`<br/>`true, T, 1 can also be used here.` |
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