OpenCL: Basic example not working. clSetKernelArg -38 Error - opencl

Question

I am attempting a very simple OpenCL example. I have developed the following code below. It compiles a simple kernel, and then I create a simple float* buffer and set it to a cl::Buffer. However, when I attempt to call the kernel.setArg() function, it crashes, with an error -38. This error states that my cl::Buffer is invalid. I have no idea why this is happening:
#define CL_HPP_ENABLE_EXCEPTIONS
#define CL_HPP_TARGET_OPENCL_VERSION 200
#include <CL/cl2.hpp>
#define MULTI_LINE_STRING(ARG) #ARG
namespace op
{
const char *resizeAndMergeKernel = MULTI_LINE_STRING(
__kernel void testKernel(__global float* image)
{
}
);
}
void testCL(){
cl::Device device;
cl::Context context;
cl::CommandQueue queue;
int deviceId = 0;
// Load Device
std::vector<cl::Platform> platforms;
std::vector<cl::Device> devices;
std::string deviceName;
cl_uint i, type;
cl::Platform::get(&platforms);
type = platforms[0].getDevices(CL_DEVICE_TYPE_GPU, &devices);
if( type == CL_SUCCESS)
{
// Get only relavent device
cl::Context allContext(devices);
std::vector<cl::Device> gpuDevices;
gpuDevices = allContext.getInfo<CL_CONTEXT_DEVICES>();
bool deviceFound = false;
for(int i=0; i<gpuDevices.size(); i++){
if(i == deviceId){
device = gpuDevices[i];
context = cl::Context(device);
queue = cl::CommandQueue(context, device, CL_QUEUE_PROFILING_ENABLE);
deviceFound = true;
cout << "Made new GPU Instance: " << deviceId << endl;
break;
}
}
if(!deviceFound)
{
throw std::runtime_error("Error: Invalid GPU ID");
}
}
// Create Kernel
cl::Program program = cl::Program(context, op::resizeAndMergeKernel, true);
cl::Kernel kernel = cl::Kernel(program, "testKernel");
// Simple Buffer
cl_int err;
float* test = new float[3*224*224];
cl::Buffer x = cl::Buffer(context, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, sizeof(float) * 3 * 224 * 224, (void*)test, &err);
cout << err << endl;
kernel.setArg(0,x); // CRASHES WITH cl::Error -38
}
As you can see the last line kernel.setArg(0,x) crashes with error -38.

Answer 1

It's not a "crash", it's an error code. OpenCL error -38 is CL_INVALID_MEM_OBJECT. It means the cl_mem_obj is not valid. It is because you are passing a cl::Buffer object to setArg, but you need to instead pass the cl_mem handle which represents that buffer. The cl::Buffer operator() method returns that. So use kernel.setArg(0,x()). Note the () are the added part (yes, it's subtle).