如何消除 opencl 代码中的 CL_INVALID_PLATFORM 错误？

使用 OpenCL 进行简单的矩阵乘法：

// Multiply two matrices A * B = C

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <oclUtils.h>

#define WA 3
#define HA 3
#define WB 3
#define HB 3
#define WC 3
#define HC 3

// Allocates a matrix with random float entries.
void randomInit(float* data, int size)
{
   for (int i = 0; i < size; ++i)
   data[i] = rand() / (float)RAND_MAX;
}

/////////////////////////////////////////////////////////
// Program main
/////////////////////////////////////////////////////////

int
main(int argc, char** argv)
{

   // set seed for rand()
   srand(2006);

   // 1. allocate host memory for matrices A and B
   unsigned int size_A = WA * HA;
   unsigned int mem_size_A = sizeof(float) * size_A;
   float* h_A = (float*) malloc(mem_size_A);

   unsigned int size_B = WB * HB;
   unsigned int mem_size_B = sizeof(float) * size_B;
   float* h_B = (float*) malloc(mem_size_B);

   // 2. initialize host memory
   randomInit(h_A, size_A);
   randomInit(h_B, size_B);

   // 3. print out A and B
   printf("\n\nMatrix A\n");
   for(int i = 0; i < size_A; i++)
   {
      printf("%f ", h_A[i]);
      if(((i + 1) % WA) == 0)
      printf("\n");
   }

   printf("\n\nMatrix B\n");
   for(int i = 0; i < size_B; i++)
   {
      printf("%f ", h_B[i]);
      if(((i + 1) % WB) == 0)
      printf("\n");
   }

   // 4. allocate host memory for the result C
   unsigned int size_C = WC * HC;
   unsigned int mem_size_C = sizeof(float) * size_C;
   float* h_C = (float*) malloc(mem_size_C);

   // 5. Initialize OpenCL
   // OpenCL specific variables
   cl_context clGPUContext;
   cl_command_queue clCommandQue;
   cl_program clProgram;
   cl_kernel clKernel;

   size_t dataBytes;
   size_t kernelLength;
   cl_int errcode;

   // OpenCL device memory for matrices
   cl_mem d_A;
   cl_mem d_B;
   cl_mem d_C;

   /*****************************************/
   /* Initialize OpenCL */
   /*****************************************/

   clGPUContext = clCreateContextFromType(0, 
                   CL_DEVICE_TYPE_GPU, 
                   NULL, NULL, &errcode);
   shrCheckError(errcode, CL_SUCCESS);

   // get the list of GPU devices associated 
   // with context
   errcode = clGetContextInfo(clGPUContext, 
              CL_CONTEXT_DEVICES, 0, NULL, 
              &dataBytes);
   cl_device_id *clDevices = (cl_device_id *)
              malloc(dataBytes);
   errcode |= clGetContextInfo(clGPUContext, 
              CL_CONTEXT_DEVICES, dataBytes, 
              clDevices, NULL);
   //shrCheckError(errcode, CL_SUCCESS);

   //Create a command-queue
   clCommandQue = clCreateCommandQueue(clGPUContext, 
                  clDevices[0], 0, &errcode);
   //shrCheckError(errcode, CL_SUCCESS);

   // Setup device memory
   d_C = clCreateBuffer(clGPUContext, 
          CL_MEM_READ_WRITE, 
          mem_size_A, NULL, &errcode);
   d_A = clCreateBuffer(clGPUContext, 
          CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, 
          mem_size_A, h_A, &errcode);
   d_B = clCreateBuffer(clGPUContext, 
          CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR, 
          mem_size_B, h_B, &errcode);


   // 6. Load and build OpenCL kernel
   char *clMatrixMul = oclLoadProgSource("kernel.cl",
                        "// My comment\n", 
                        &kernelLength);
   //shrCheckError(clMatrixMul != NULL, shrTRUE);

   clProgram = clCreateProgramWithSource(clGPUContext, 
                1, (const char **)&clMatrixMul, 
                &kernelLength, &errcode);
   //shrCheckError(errcode, CL_SUCCESS);

   errcode = clBuildProgram(clProgram, 0, 
              NULL, NULL, NULL, NULL);
   //shrCheckError(errcode, CL_SUCCESS);

   clKernel = clCreateKernel(clProgram, 
               "matrixMul", &errcode);
   //shrCheckError(errcode, CL_SUCCESS);


   // 7. Launch OpenCL kernel
   size_t localWorkSize[2], globalWorkSize[2];

   int wA = WA;
   int wC = WC;
   errcode = clSetKernelArg(clKernel, 0, 
              sizeof(cl_mem), (void *)&d_C);
   errcode |= clSetKernelArg(clKernel, 1, 
              sizeof(cl_mem), (void *)&d_A);
   errcode |= clSetKernelArg(clKernel, 2, 
              sizeof(cl_mem), (void *)&d_B);
   errcode |= clSetKernelArg(clKernel, 3, 
              sizeof(int), (void *)&wA);
   errcode |= clSetKernelArg(clKernel, 4, 
              sizeof(int), (void *)&wC);
   //shrCheckError(errcode, CL_SUCCESS);

   localWorkSize[0] = 3;
   localWorkSize[1] = 3;
   globalWorkSize[0] = 3;
   globalWorkSize[1] = 3;

   errcode = clEnqueueNDRangeKernel(clCommandQue, 
              clKernel, 2, NULL, globalWorkSize, 
              localWorkSize, 0, NULL, NULL);
   //shrCheckError(errcode, CL_SUCCESS);

   // 8. Retrieve result from device
   errcode = clEnqueueReadBuffer(clCommandQue, 
              d_C, CL_TRUE, 0, mem_size_C, 
              h_C, 0, NULL, NULL);
   //shrCheckError(errcode, CL_SUCCESS);

   // 9. print out the results
   printf("\n\nMatrix C (Results)\n");
   for(int i = 0; i < size_C; i++)
   {
      printf("%f ", h_C[i]);
      if(((i + 1) % WC) == 0)
      printf("\n");
   }
   printf("\n");

   // 10. clean up memory
   free(h_A);
   free(h_B);
   free(h_C);

   clReleaseMemObject(d_A);
   clReleaseMemObject(d_C);
   clReleaseMemObject(d_B);

   free(clDevices);
   free(clMatrixMul);
   clReleaseContext(clGPUContext);
   clReleaseKernel(clKernel);
   clReleaseProgram(clProgram);
   clReleaseCommandQueue(clCommandQue);

}

在上面的代码中，我不断在这个地方收到错误：

/**********************/ /

Nvidia 驱动程序希望您提供一个非 NULL 属性指针作为第一个参数clCreateContextFromType call.

Khronos 规范clCreateContextFromType指出如果为属性参数传递 NULL，则选择的平台取决于实现。对于 Nvidia，选择似乎是如果传递 NULL 指针，则根本不选择任何平台。看clCreateContextFromType http://www.khronos.org/registry/cl/sdk/1.2/docs/man/xhtml/clCreateContextFromType.html了解更多信息。

另一方面，此行为与问题 #3 一致cl_khr_icd 扩展 http://www.khronos.org/registry/cl/extensions/khr/cl_khr_icd.txt，如果您通过 ICD 使用 OpenCL，则适用，其中指出：

3: How will the ICD handle a NULL cl_platform_id?

RESOLVED: The NULL platform is not supported by the ICD.

将属性传递给clCreateContextFromType，首先查询平台clGetPlatformIDs。然后使用所需的平台 ID 构造一个属性数组并将其传递给clCreateContextFromType。以下内容应该适用于 C99 兼容的编译器：

   // query the number of platforms
   cl_uint numPlatforms;
   errcode = clGetPlatformIDs(0, NULL, &numPlatforms);
   shrCheckError(errcode, CL_SUCCESS); 

   // now get all the platform IDs
   cl_platform_id platforms[numPlatforms];
   errcode = clGetPlatformIDs(numPlatforms, platforms, NULL);
   shrCheckError(errcode, CL_SUCCESS);

   // set platform property - we just pick the first one
   cl_context_properties properties[] = {CL_CONTEXT_PLATFORM, (int) platforms[0], 0};
   clGPUContext = clCreateContextFromType(properties, CL_DEVICE_TYPE_GPU, NULL, NULL, &errcode);
   shrCheckError(errcode, CL_SUCCESS);