C Specification

To set the argument value for a specific argument of a kernel, call the function

cl_int clSetKernelArg(
    cl_kernel kernel,
    cl_uint arg_index,
    size_t arg_size,
    const void* arg_value);

Parameters

  • kernel is a valid kernel object.

  • arg_index is the argument index. Arguments to the kernel are referred by indices that go from 0 for the leftmost argument to n - 1, where n is the total number of arguments declared by a kernel (see below).

  • arg_size specifies the size of the argument value. If the argument is a memory object, the arg_size value must be equal to sizeof(cl_mem). For arguments declared with the local qualifier, the size specified will be the size in bytes of the buffer that must be allocated for the local argument. If the argument is of type sampler_t, the arg_size value must be equal to sizeof(cl_sampler). If the argument is of type queue_t, the arg_size value must be equal to sizeof(cl_command_queue). For all other arguments, the size will be the size of argument type.

  • arg_value is a pointer to data that should be used as the argument value for argument specified by arg_index. The argument data pointed to by arg_value is copied and the arg_value pointer can therefore be reused by the application after clSetKernelArg returns. The argument value specified is the value used by all API calls that enqueue kernel (clEnqueueNDRangeKernel and clEnqueueTask) until the argument value is changed by a call to clSetKernelArg for kernel.

Description

For example, consider the following kernel:

kernel void image_filter (int n,
                          int m,
                          constant float *filter_weights,
                          read_only image2d_t src_image,
                          write_only image2d_t dst_image)
{
...
}

Argument index values for image_filter will be 0 for n, 1 for m, 2 for filter_weights, 3 for src_image and 4 for dst_image.

If the argument is a memory object (buffer, pipe, image or image array), the arg_value entry will be a pointer to the appropriate buffer, pipe, image or image array object. The memory object must be created with the context associated with the kernel object. If the argument is a buffer object, the arg_value pointer can be NULL or point to a NULL value in which case a NULL value will be used as the value for the argument declared as a pointer to global or constant memory in the kernel. If the argument is declared with the local qualifier, the arg_value entry must be NULL. If the argument is of type sampler_t, the arg_value entry must be a pointer to the sampler object. If the argument is of type queue_t, the arg_value entry must be a pointer to the device queue object.

If the argument is declared to be a pointer of a built-in scalar or vector type, or a user defined structure type in the global or constant address space, the memory object specified as argument value must be a buffer object (or NULL). If the argument is declared with the constant qualifier, the size in bytes of the memory object cannot exceed CL_​DEVICE_​MAX_​CONSTANT_​BUFFER_​SIZE and the number of arguments declared as pointers to constant memory cannot exceed CL_​DEVICE_​MAX_​CONSTANT_​ARGS.

The memory object specified as argument value must be a pipe object if the argument is declared with the pipe qualifier.

The memory object specified as argument value must be a 2D image object if the argument is declared to be of type image2d_t. The memory object specified as argument value must be a 2D image object with image channel order = CL_​DEPTH if the argument is declared to be of type image2d_depth_t. The memory object specified as argument value must be a 3D image object if argument is declared to be of type image3d_t. The memory object specified as argument value must be a 1D image object if the argument is declared to be of type image1d_t. The memory object specified as argument value must be a 1D image buffer object if the argument is declared to be of type image1d_buffer_t. The memory object specified as argument value must be a 1D image array object if argument is declared to be of type image1d_array_t. The memory object specified as argument value must be a 2D image array object if argument is declared to be of type image2d_array_t. The memory object specified as argument value must be a 2D image array object with image channel order = CL_​DEPTH if argument is declared to be of type image2d_array_depth_t.

For all other kernel arguments, the arg_value entry must be a pointer to the actual data to be used as argument value.

A kernel object does not update the reference count for objects such as memory or sampler objects specified as argument values by clSetKernelArg. Users may not rely on a kernel object to retain objects specified as argument values to the kernel.

Implementations shall not allow cl_kernel objects to hold reference counts to cl_kernel arguments, because no mechanism is provided for the user to tell the kernel to release that ownership right. If the kernel holds ownership rights on kernel args, that would make it impossible for the user to tell with certainty when he may safely release user allocated resources associated with OpenCL objects such as the cl_mem backing store used with CL_​MEM_​USE_​HOST_​PTR.

clSetKernelArg returns CL_​SUCCESS if the function was executed successfully. Otherwise, it returns one of the following errors:

  • CL_​INVALID_​KERNEL if kernel is not a valid kernel object.

  • CL_​INVALID_​ARG_​INDEX if arg_index is not a valid argument index.

  • CL_​INVALID_​ARG_​VALUE if arg_value specified is not a valid value.

  • CL_​INVALID_​MEM_​OBJECT for an argument declared to be a memory object when the specified arg_value is not a valid memory object.

  • CL_​INVALID_​SAMPLER for an argument declared to be of type sampler_t when the specified arg_value is not a valid sampler object.

  • CL_​INVALID_​DEVICE_​QUEUE for an argument declared to be of type queue_t when the specified arg_value is not a valid device queue object. This error code is missing before version 2.0.

  • CL_​INVALID_​ARG_​SIZE if arg_size does not match the size of the data type for an argument that is not a memory object or if the argument is a memory object and arg_size != sizeof(cl_mem) or if arg_size is zero and the argument is declared with the local qualifier or if the argument is a sampler and arg_size != sizeof(cl_sampler).

  • CL_​MAX_​SIZE_​RESTRICTION_​EXCEEDED if the size in bytes of the memory object (if the argument is a memory object) or arg_size (if the argument is declared with local qualifier) exceeds a language- specified maximum size restriction for this argument, such as the MaxByteOffset SPIR-V decoration. This error code is missing before version 2.2.

  • CL_​INVALID_​ARG_​VALUE if the argument is an image declared with the read_only qualifier and arg_value refers to an image object created with cl_mem_flags of CL_​MEM_​WRITE_​ONLY or if the image argument is declared with the write_only qualifier and arg_value refers to an image object created with cl_mem_flags of CL_​MEM_​READ_​ONLY.

  • CL_​OUT_​OF_​RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.

  • CL_​OUT_​OF_​HOST_​MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

See Also

Document Notes

For more information, see the OpenCL Specification

This page is extracted from the OpenCL Specification. Fixes and changes should be made to the Specification, not directly.

Copyright (c) 2014-2020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.