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Waf and OpenCL check

Although I am quite used to CMake and the infamous Autotools, I wanted to try out the Waf build system for a smallish side project that I am investigating with a fellow student of mine. This project has a limited number of dependencies which could also be integrated in a simple Makefile but it also needs to detect the include path and the libraries of any OpenCL installation. Unfortunately, neither NVIDIA’s nor AMD’s OpenCL distribution is installed in a standards compliant way. Although the NVIDIA installation procedure suggests to install the CUDA toolkit into /usr/local, it does so by creating a new root folder /usr/local/cuda with bin, lib, include and a bunch of non-UNIX directories right beneath. But I don’t want to complain, let’s head right in how to solve this.

Download the latest Waf distribution file and create an empty wscript file in your source directory. This file is used to configure – check if required and optional dependencies are met – and build your project. Because it contains real Python code, you can configure your project in any imaginable way.

The configuration and build steps are mapped to the configure() and build() functions. To compile C source files, we need to tell the system which translation facility to use:

def configure(conf):
    conf.load('compiler_c')
    conf.env.append_unique('CFLAGS', ['-g', '-std=c99', '-O3', '-Wall', '-Werror' ])

def build(bld):
    bld.program(source='foo.c', target='foo')

As you can see, additional CFLAGS are appended through the env objects append_x methods. For some reason, we must also load the compiler in a preceding options step, which tells the build system to export the compiler’s command line options:

def options(opt):
    opt.load('compiler_c')

Most Linux distributions ship pkg-config files for the majority of libraries. Fortunately, Waf is able to call the pkg-config binary out-of-the-box with the check_cfg function.

However, the NVIDIA installer copies the header files in non-standard locations and does not provide any .pc files. In most cases, the user will just hit the enter key when prompted by the installer where to put the files, thus copying it to /usr/local/cuda. Others, like me, try to keep non-standard things in /opt or place the distribution in their home directory and set the suggested in environment variables. To cover these cases, we can compute a list with existing paths:

def guess_cl_include_path():
    import os

    OPENCL_INC_PATHS = [
        '/usr/local/cuda/include',
        '/opt/cuda/include'
    ]

    try:
        OPENCL_INC_PATHS.append(os.environ['CUDA_INC_PATH'])
    except:
        pass

    return filter(lambda d: os.path.exists(d), OPENCL_INC_PATHS)

We plug this little function into the configure function, tell the user what’s going on with start_msg() and abort with fatal() in case we cannot find anything. Last but not least, we add a check with check_cc() for libOpenCL.so which should be installed in one of the standard library paths. The final configure step looks like this:

def configure(conf):
    conf.load('compiler_c')
    conf.env.append_unique('CFLAGS', ['-g', '-std=c99', '-O3', '-Wall', '-Werror' ])
    
    # use pkg-config
    conf.check_cfg(package='glib-2.0', args='--cflags --libs', uselib_store='GLIB2')

    conf.start_msg('Checking for OpenCL include path')
    incs = guess_cl_include_path()

    if incs:
        conf.env.OPENCL_INC_PATH = incs[0]
        conf.end_msg('found')
    else:
        conf.fatal('OpenCL include path not found')

    conf.check_cc(lib='OpenCL', uselib_store='CL')

Configure information is stored across builds using the env structure and the uselib_store keyword. When building the binary, we refer to the these variables and we are good to go:

def build(bld):
    bld.program(source='foo.c', 
        target='foo', 
        use=['GLIB2', 'CL'], 
        includes=bld.env.OPENCL_INC_PATH)

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