global date being transferred to the host

Accelerated Computing CUDA CUDA Programming and Performance
1

I have an global array struct which is allocated in host while it’s element pointer is dynamic allocated in device function. I have to copy the result from device to host and use cudaMemcpyFromSymbol, but it comes to a segmentation fault.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define cudaSafeCall(call){
cudaError err = call;
if(cudaSuccess != err){
fprintf(stderr, “%s(%i) : %s.\n”, FILE, LINE, cudaGetErrorString(err));
exit(EXIT_FAILURE);
}}

struct num{
int *a;
int b;
};

device struct num gun;
int main(int argc, char argv[])
{
int result;
struct num cun,dcun;
cudaSafeCall(cudaSetDevice(1));
dcun=(struct num)malloc(10sizeof(struct num));
cudaMalloc(&result,sizeof(int));
cudaMalloc(&cun,10sizeof(struct num));
cudaMemcpyToSymbol(gun,&cun,sizeof(struct num));
timeval tv, tv1;
global void kernel(int);
gettimeofday(&tv, 0);
kernel<<<1,10>>>(result);
cudaDeviceSynchronize();
gettimeofday(&tv1, 0);
cudaMemcpyFromSymbol(cun,&gun,sizeof(struct num*));
cudaMemcpy(dcun,cun,10sizeof(struct num),cudaMemcpyDeviceToHost);
cudaMemcpy(dcun->a,cun->a,10sizeof(int),cudaMemcpyDeviceToHost);//segmentation fault
printf("%d “,dcun[8].b);
printf(”%d “,dcun[9].a[9]);//segmentation fault
cudaFree(cun);
cudaFree(result);
free(dcun);
printf(”%f ",tv1.tv_sec-tv.tv_sec + (double)(tv1.tv_usec-tv.tv_usec)/CLOCKS_PER_SEC);
}

global void kernel(int result)
{
int k=2;
result=k;
int i;
int tid=threadIdx.x;
gun[tid].b=tid;
gun[tid].a=(int)malloc(10sizeof(int));
for(i=0;i<10;i++)
gun[tid].a[i]=tid+i;
}

Why can’t I transfer the struct’s pointer element while the transfer of the struct’s constant is succeed? Is it because that the pointer element is dynamic allocated in device function? What can I do?

2

You are copying data from the device to the same address in the host address space, which most likely is an illegal address. You need to allocate space on the host (which will get a different address) and then copy to that address.

3

I can not understand what you mean.Do you mean that I need to allocate a new struct num pointer to get the device address?Can you give me an example?Thanks!