This repo contains the source code and tests for the Khronos official OpenCL ICD Loader.

OpenCL 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. The ICD Loader is responsible for:

• Exporting OpenCL API entry points
• Enumerating OpenCL implementations
• Forwarding OpenCL API calls to the correct implementation

This repo contains the source code and tests for the Khronos official OpenCL ICD Loader.

Note that this repo does not contain an OpenCL implementation (ICD). You 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.

The OpenCL Installable Client Driver extension (cl_khr_icd) is described in the OpenCL extensions specification, which may be found on the Khronos OpenCL Registry.

While the ICD Loader can be built and installed in isolation, it is part of the OpenCL SDK. If looking for streamlined build experience and a complete development package, refer to the SDK build instructions instead of the following guide.

The OpenCL ICD Loader requires:

• the OpenCL Headers.
  • 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.
• The OpenCL ICD Loader uses CMake for its build system. If CMake is not provided by your build system or OS package manager, please consult the CMake website.

For most Windows and Linux usages, the following steps are sufficient to build the OpenCL ICD Loader:

1. Clone this repo and the OpenCL Headers:

    git clone https://github.com/KhronosGroup/OpenCL-ICD-Loader
    git clone https://github.com/KhronosGroup/OpenCL-Headers
   

2. Install OpenCL Headers CMake package

    cmake -D CMAKE_INSTALL_PREFIX=./OpenCL-Headers/install -S ./OpenCL-Headers -B ./OpenCL-Headers/build 
    cmake --build ./OpenCL-Headers/build --target install
   

3. Build and install OpenCL ICD Loader CMake package. (Note that CMAKE_PREFIX_PATH need to be an absolute path. Update as needed.)

    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 
    cmake --build ./OpenCL-ICD-Loader/build --target install
   

Notes:

• For x64 Windows builds, you need to instruct the default Visual Studio generator by adding -A x64 to all your command-lines.

• Some users may prefer to use a CMake GUI frontend, such as cmake-gui or ccmake, vs. the command-line CMake.

Example CMake invocation

cmake -D CMAKE_PREFIX_PATH="/chosen/install/prefix/of/headers;/chosen/install/prefix/of/loader" /path/to/opencl/app

and sample CMakeLists.txt

cmake_minimum_required(VERSION 3.0)
cmake_policy(VERSION 3.0...3.18.4)
project(proj)
add_executable(app main.cpp)
find_package(OpenCLHeaders REQUIRED)
find_package(OpenCLICDLoader REQUIRED)
target_link_libraries(app PRIVATE OpenCL::Headers OpenCL::OpenCL)

OpenCL 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.

(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.)

The method to installing an ICD is operating system dependent.

Install your ICD by creating a file with the full path to the library of your implementation in /etc/OpenCL/vendors for eg.:

echo full/path/to/libOpenCLDriverStub.so > /etc/OpenCL/vendors/test.icd

Install your ICD by adding a REG_DWORD value to the registry keys:

// For 32-bit operating systems, or 64-bit tests on a 64-bit operating system:
HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenCL\Vendors

// For 32-bit tests on a 64-bit operating system:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Khronos\OpenCL\Vendors

// The name of the REG_DWORD value should be the full path to the library of your implementation, for eg.
// OpenCLDriverStub.dll, and the data for this value should be 0.

Layers have been added as an experimental feature in the OpenCL ICD Loader. We do not expect the API or ABI to change significantly, but the OpenCL Working Group reserves the right to do so. The layer support can also be completely deactivated during configuration by using the ENABLE_OPENCL_LAYERS (ON by default) cmake variable:

cmake -DENABLE_OPENCL_LAYERS=OFF

For now, runtime configuration of layers is done using the OPENCL_LAYERS environment variable. A colon (Linux) or semicolon (Windows) list of layers to use can be provided through this environment variable.

We are looking for feedback.

Please create a GitHub issue to report an issue or ask questions.

Contributions to the OpenCL ICD Loader are welcomed and encouraged. You will be prompted with a one-time "click-through" CLA dialog as part of submitting your pull request or other contribution to GitHub.

The following debug environment variables are available for use with the OpenCL ICD loader: