Information for Developers

Using cmake to build & install pocl

Most of the important stuff on using cmake is in the INSTALL file. A few additional items:



command must point to ocl-vendors in the cmake build directory, not the pocl source directory.

Testing is done using either “make test” or invoking “ctest” directly; “make check” does not work. Invoke ctest with -jX option to run X tests in parallel.


Before changes are committed to the mainline, all tests in the ‘make check’ suite should pass:

make check

Under the ‘examples’ directory there are placeholder directories for external OpenCL application projects which are used as test suites for pocl (e.g. ViennaCL). These test suites can be enabled for cmake with -DENABLE_TESTSUITES (you can specify a list of test suites if you do not want to enabled all of them, see configure help for the available list). Note that these additionnal test suites require additionnal software (tools and libraries). The configure script checks some of them but the check is not exhautive. Test suites are disabled if their requirement files are not available.

In order to prepare the external OpenCL examples for the testsuite, you need to run the following build command once:

make prepare_examples

IMPORTANT: using the ICD for in tree ‘make check’ requires an icd loader that allows overriding the icd search path. Other ICD loaders wont be able to work in tree (they require the ICD config file to be installed in the system). There are now two options for such a loder: the open source ocl-icd loader and the Khronos supplied loader with a patch applied.

Debugging a Failed Test

If there are failing tests in the suite, the usual way to start debugging is to look what was printed to the logs for the failing cases. After running the test suite, the logs are stored under Testing/Temporary/*.log


ocl-icd can be downloaded from It allows overriding the path from which the icd files are searched which is used to select only the OpenCL library in the build tree of pocl for the make check. Note, however, if you run the tests or examples manually this overriding is not done automatically. To direct the ocl-icd to use only the pocl in the build tree, export the following environment variable in your shell:


Inside the ‘ocl-vendors’ directory there’s a single .icd file which is generated to point to the pocl library in the build tree.

Coding Style

The code base of pocl consists most of pure C sources and C++ sources (mostly the kernel compiler).

  1. In the C sources, follow the GNU style.

  2. In the C++ sources (mostly the LLVM passes), follow the LLVM coding guidelines so it is easier to upstream general code to the LLVM project at any point.

It’s acknowledged that the pocl code base does fully not adhere to these principles at the moment, but the aim is to gradually fix the style and any new code merged to master should adhere to them.

Khronos ICD Loader

The ICD loader supplied by Khronos can be used for pocl development by applying a minor patch that enables overriding the ICD search path as explained above (OCL-ICD).

The steps to build and install the Khronos ICD loader so it can be used to run the pocl test suite:

  1. Download the loader from Unpack it. Copy the OpenCL headers to inc/CL like instructed in inc/README.txt.

  2. Apply a patch from the pocl checkout::

    cd icd

    patch -p1 < ~/pocl/tools/patches/khronos-icd-loader.patch

  3. Build it with ‘make’.

  4. Copy the loader to a library search path: sudo cp bin/libOpenCL* /usr/lib

Now it should use the Khronos loader for ICD dispatching and you (and the pocl build system) should be able to override the icd search path with OCL_ICD_VENDORS environment variable.

Using pocl from the Build Tree

If you want use the pocl from the build tree, you must export POCL_BUILDING=1 so pocl searches for its utility scripts from the build tree first, then the installation location. The “make check” testsuite does this automatically.

There’s a helper script that, when sourced, in addition to setting POCL_BUILDING setups the OCL_ICD_VENDORS path to point to the pocl in the build tree. This removes the need to install pocl to test the built version. It should be executed in the build root, typically:

. ../tools/scripts/

Target and Host CPU Architectures for ‘basic’ and ‘pthread’ Devices

By default, pocl build system compiles the kernel libraries for the host CPU architecture, to be used by ‘basic’ and ‘pthread’ devices.

LLVM is used to detect the CPU variant to be used as target. This can be overridden by passing LLC_HOST_CPU to ‘./configure’. Valid options are best documented in the output of:

llvm-as /dev/null | llc -mcpu=help

Cross-compilation where ‘build’ is different from ‘host’ has not been tested. Cross-compilation where ‘host’ is a different architecture from ‘target’ has not been tested for ‘basic’ and ‘pthread’ devices.

Writing Documentation

The documentation is written using the Sphinx documentation generator and the reStructuredText markup.

This Sphinx documentation can be built by:

cd doc/sphinx
make html

This builds the html version of the documents under the ‘build/html’ directory.