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Using the Intercept Layer for OpenCL Applications

Part 1: Fixing an OpenCL Error

In this part of the tutorial we will fix a bug so the program will no longer crash. The Intercept Layer for OpenCL Applications can easily identify OpenCL errors in a program and provide clues why the OpenCL error might be occurring.

To find where this OpenCL error is occurring, enable the controls ErrorLogging and CallLogging. Please refer to the controls page for instructions how to enable these controls and other controls that will be used throughout the tutorial. Note that CallLogging can be enabled by passing the -c option to cliloader and does not necessarily need to be enabled manually.

After enabling these controls, re-run the tutorial application.

$ cliloader ./sinjulia
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
CLIntercept (64-bit) is loading...
CLIntercept file location: /home/bashbaug/bin/../lib/libOpenCL.so
CLIntercept URL: https://github.com/intel/opencl-intercept-layer
CLIntercept git description: v3.0.0-11-gd73caba
CLIntercept git refspec: refs/heads/master
CLIntercept git hash: d73caba0273207c47d3094865c1a9e145acf2018
CLIntercept optional features:
    cliloader(supported)
    cliprof(supported)
    kernel overrides(supported)
    ITT tracing(NOT supported)
    MDAPI(supported)
    clock(steady_clock)
CLIntercept environment variable prefix: CLI_
CLIntercept config file: clintercept.conf
Trying to load dispatch from: ./real_libOpenCL.so
Couldn't load library: ./real_libOpenCL.so
Trying to load dispatch from: /usr/lib/x86_64-linux-gnu/libOpenCL.so.1
Couldn't get exported function pointer to: clGetGLContextInfoKHR
... success!
Control CallLogging is set to non-default value: true
Control ErrorLogging is set to non-default value: true
Control ReportToStderr is set to non-default value: true
Timer Started!
... loading complete.
>>>> clGetPlatformIDs
<<<< clGetPlatformIDs -> CL_SUCCESS
>>>> clGetPlatformIDs
<<<< clGetPlatformIDs -> CL_SUCCESS
*** Important Note! ***
This is the Intercept Layer Tutorial application.
It will crash initially!  Please see the tutorial README for details.
>>>> clGetPlatformInfo: platform = Intel(R) OpenCL HD Graphics (0x55637a388e20), param_name = CL_PLATFORM_NAME (00000902)
<<<< clGetPlatformInfo -> CL_SUCCESS
>>>> clGetPlatformInfo: platform = Intel(R) OpenCL HD Graphics (0x55637a388e20), param_name = CL_PLATFORM_NAME (00000902)
<<<< clGetPlatformInfo -> CL_SUCCESS
Running on platform: Intel(R) OpenCL HD Graphics
>>>> clGetDeviceIDs: platform = Intel(R) OpenCL HD Graphics (0x55637a388e20), device_type = <unknown> (1000)
ERROR! clGetDeviceIDs returned CL_INVALID_DEVICE_TYPE (-31)
<<<< clGetDeviceIDs -> CL_INVALID_DEVICE_TYPE
Segmentation fault (core dumped)

There are two parts of this output to pay attention to. First, ensure that the controls have been properly enabled:

Control CallLogging is set to non-default value: true
Control ErrorLogging is set to non-default value: true

If ErrorLogging and CallLogging are not "set to non-default values" then the controls are not enabled properly.

Second, observe that that the call to clGetDeviceIDs is failing and is returning CL_INVALID_DEVICE_TYPE. Furthermore, observe that the passed-in device_type is unrecognized. Because the call to clGetDeviceIDs is failing, we don't have any OpenCL devices to choose from, and since the tutorial application does not gracefully handle this case it is crashing. Let's pass in a proper device type so we have OpenCL devices to choose from.

// Part 1: Query the devices in this platform.
// When querying for OpenCL devices we pass the types of devices we want to
// query. This will either be one or more specific device types, e.g.
// CL_DEVICE_TYPE_CPU, or we can pass in CL_DEVICE_TYPE_ALL, which will get
// all devices. Passing CL_DEVICE_TYPE isn't a valid device type and will
// result in an OpenCL error. What should we pass instead?
platforms[platformIndex].getDevices(CL_DEVICE_TYPE, &devices);

After fixing this bug the tutorial application should be able to query devices in the platform and should no longer crash.

Move on to part 2!

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