How to copy the memeory allocated in device function back to main memory
- by xhe8
I have a CUDA program containing a host function and a device function Execute(). In the host function, I allocate a global memory output which will then be passed to the device function and used to store the address of the global memory allocated within the device function. I want to access the in-kernel allocated memory in the host function. The following is the code:
#include <stdio.h>
typedef struct
{
int * p;
int num;
} Structure_A;
\__global__ void Execute(Structure_A *output);
int main(){
Structure_A *output;
cudaMalloc((void***)&output,sizeof(Structure_A)*1);
dim3 dimBlockExecute(1,1);
dim3 dimGridExecute(1,1);
Execute<<<dimGridExecute,dimBlockExecute>>>(output);
Structure_A * output_cpu;
int * p_cpu;
cudaError_t err;
output_cpu= (Structure_A*)malloc(1);
err=cudaMemcpy(output_cpu,output,sizeof(Structure_A),cudaMemcpyDeviceToHost);
if( err != cudaSuccess)
{
printf("CUDA error a: %s\n", cudaGetErrorString(err));
exit(-1);
}
p_cpu=(int *)malloc(1);
err=cudaMemcpy(p_cpu,output_cpu[0].p,sizeof(int),cudaMemcpyDeviceToHost);
if( err != cudaSuccess)
{
printf("CUDA error b: %s\n", cudaGetErrorString(err));
exit(-1);
}
printf("output=(%d,%d)\n",output_cpu[0].num,p_cpu[0]);
return 0;
}
\__global__ void Execute(Structure_A *output){
int thid=threadIdx.x;
output[thid].p= (int*)malloc(thid+1);
output[thid].num=(thid+1);
output[thid].p[0]=5;
}
I can compile the program. But when I run it, I got a error showing that there is a invalid argument in the following memory copy function. "err=cudaMemcpy(p_cpu,output_cpu[0].p,sizeof(int),cudaMemcpyDeviceToHost);"
CUDA version is 4.2.
CUDA card: Tesla C2075
OS: x86_64 GNU/Linux
