Load device function from shared library with dlopen - cuda

Question

I'm relatively new to cuda programming and can't find a solution to my problem.
I'm trying to have a shared library, lets call it func.so, that defines a device function
__device__ void hello(){ prinf("hello");}
I then want to be able to access that library via dlopen, and use that function in my programm. I tried something along the following lines:
func.cu
#include <stdio.h>
typedef void(*pFCN)();
__device__ void dhello(){
printf("hello\n")
}
__device__ pFCN ptest = dhello;
pFCN h_pFCN;
extern "C" pFCN getpointer(){
cudaMemcpyFromSymbol(&h_pFCN, ptest, sizeof(pFCN));
return h_pFCN;
}
main.cu
#include <dlfcn.h>
#include <stdio.h>
typedef void (*fcn)();
typedef fcn (*retpt)();
retpt hfcnpt;
fcn hfcn;
__device__ fcn dfcn;
__global__ void foo(){
(*dfcn)();
}
int main() {
void * m_handle = dlopen("gputest.so", RTLD_NOW);
hfcnpt = (retpt) dlsym( m_handle, "getpointer");
hfcn = (*hfcnpt)();
cudaMemcpyToSymbol(dfcn, &hfcn, sizeof(fcn), 0, cudaMemcpyHostToDevice);
foo<<<1,1>>>();
cudaThreadSynchronize();
return 0;
}
But this way I get the following error when debugging with cuda-gdb:
CUDA Exception: Warp Illegal Instruction
Program received signal CUDA_EXCEPTION_4, Warp Illegal Instruction.
0x0000000000806b30 in dtest () at func.cu:5
I appreciate any help you all can give me! :)

Answer 1

Calling a __device__ function in one compilation unit from device code in another compilation unit requires separate compilation with device linking usage of nvcc.
However, such usage with libraries only works with static libraries.
Therefore if the target __device__ function is in the .so library, and the calling code is outside of the .so library, your approach cannot work, with the current nvcc toolchain.
The only "workarounds" I can suggest would be to put the desired target function in a static library, or else put both caller and target inside the same .so library. There are a number of questions/answers on the cuda tag which give examples of these alternate approaches.