Question

I’m having trouble passing a vector type (uint8) parameter to an OpenCL kernel function from the host code in C.

In the host I’ve got the data in an array:

cl_uint dataArr[8] = { 1, 2, 3, 4, 5, 6, 7, 8 };

(My real data is more than just [1, 8]; this is just for ease of explanation.)

I then transfer the data over to a buffer to be passed to the kernel:

cl_mem kernelInputData = clCreateBuffer(context,
    CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, sizeof(cl_uint)*8, dataArr, NULL);

Next, I pass this buffer into the kernel:

clSetKernelArg(kernel, 0, sizeof(cl_mem), &kernelInputData);

And the kernel function’s signature looks something like this:

kernel void kernelFunction(constant uint8 *vectorPtr)

However, the kernel doesn’t seem to be obtaining the correct input data from the pointer to kernelInputData. When I pass values back from within the kernel, I see that vectorPtr points to something with this structure: ( 1, 2, 3, 4, 5, ?, ?, ? ) where the question marks are usually 4293848814 but sometimes 0. Either way, not what they’re supposed to be.

What am I doing wrong?

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EDIT:

I’ve switched from using an array to cl_uint8 on the host side. I now have:

cl_uint8 dataVector = { 1, 2, 3, 4, 5, 6, 7, 8 };

And I pass this vector to the kernel like so:

clSetKernelArg(kernel, 0, sizeof(cl_uint8), &dataVector);

And the kernel function’s signature looks something like this:

kernel void kernelFunction(constant uint8 *vectorPtr)

However, running this code gives me a CL_INVALID_ARG_SIZE error on clSetKernelArg(). This error goes away if I switch the ARG_SIZE paramater to sizeof(cl_uint8 *) but then I get an EXC_BAD_ACCESS error in __dynamic_cast within clSetKernelArg().

My device is:

Apple Macbook Pro (mid-2009)
OSX 10.8 Mountain Lion
NVIDIA GeForce 9400M
OpenCL 1.0
CLH 1.0

Answer 1

You are defining an array of cl_uint of size 8.
The creation of the cl_mem and the setting of kernel argument are right.
But your kernel argument isn’t correct: you try to read an array of cl_uint8 instead of cl_uint.

If you want to use a vector data type, you must declare: cl_uint8 dataArr of size 1.
Or if you want to use an array of size 8: kernel void kernelFunction(constant uint *vectorPtr, uint size):

Edit:

The kernel parameter for cl_uint8 dataVector is not a pointer.
So, the correct code is:

cl_uint8 dataVector = { 1, 2, 3, 4, 5, 6, 7, 8 };
clSetKernelArg(kernel, 0, sizeof(cl_uint8), &dataVector);

and

kernel void kernelFunction(constant uint8 vectorPtr)