Update project from older CUDA version - cuda

Question

In my older CUDA project I had the globals:
__device__ uint8_t dev_intersect
__constant__ uint8_t dev_flags
... and used them this way:
cudaGetSymbolAddress((void**)&ptr_dev_intersect,"dev_intersect")
cudaMemcpyToSymbol("dev_flags",&flags,sizeof(flags))
Now, since CUDA 5.0 (and newer) the symbols must be passed directly (without string), so I define the globals this way:
__device__ uint8_t *dev_intersect
__constant__ uint8_t *dev_flags
...and call the functions this way:
cudaGetSymbolAddress((void**)&ptr_dev_intersect,dev_intersect)
cudaMemcpyToSymbol(dev_flags,&flags,sizeof(flags))
Am I doing it right so far? I'm asking you, because when I update the code, I start getting other errors, which makes me kinda suspicious. Thanks for any help.

Answer 1

Switching from a POD variable to a pointer is probably not what you want.
If you didn't make changes elsewhere in your code to account for that difference, I would expect things to break.
To update your cuda function calls, leave your variables as-is:
__device__ uint8_t dev_intersect;
__constant__ uint8_t dev_flags;
And just drop the quotes from your cuda API functions that use those variables:
cudaGetSymbolAddress((void**)&ptr_dev_intersect,dev_intersect);
cudaMemcpyToSymbol(dev_flags,&flags,sizeof(flags));
Here is a complete worked example:
$ cat t524.cu
#include <stdio.h>
typedef unsigned char uint8_t;
__device__ uint8_t dev_intersect;
__constant__ uint8_t dev_flags;
__global__ void mykernel(uint8_t *d1_ptr){
printf("data 1 = %c\n", *d1_ptr);
printf("dev_flags = %c\n", dev_flags);
}
int main(){
uint8_t *ptr_dev_intersect;
uint8_t flags = 'X';
uint8_t dev_intersect_data = 'Y';
cudaGetSymbolAddress((void**)&ptr_dev_intersect,dev_intersect);
cudaMemcpyToSymbol(dev_flags,&flags,sizeof(flags));
cudaMemcpyToSymbol(dev_intersect,&dev_intersect_data,sizeof(dev_intersect_data));
mykernel<<<1,1>>>(ptr_dev_intersect);
cudaDeviceSynchronize();
return 0;
}
$ nvcc -arch=sm_20 -o t524 t524.cu
$ cuda-memcheck ./t524
========= CUDA-MEMCHECK
data 1 = Y
dev_flags = X
========= ERROR SUMMARY: 0 errors
$