Question

I am trying separate a CUDA program into two separate .cu files in effort to edge closer to writing a real app in C++. I have a simple little program that:

Allocates a memory on the host and the device.
Initializes the host array to a series of numbers.
Copies the host array to a device array
Finds the square of all the elements in the array using a device kernel
Copies the device array back to the host array
Prints the results

This works great if I put it all in one .cu file and run it. When I split it into two separate files I start getting linking errors. Like all my recent questions, I know this is something small, but what is it?

KernelSupport.cu

#ifndef _KERNEL_SUPPORT_
#define _KERNEL_SUPPORT_

#include <iostream>
#include <MyKernel.cu>

int main( int argc, char** argv) 
{
    int* hostArray;
    int* deviceArray;
    const int arrayLength = 16;
    const unsigned int memSize = sizeof(int) * arrayLength;

    hostArray = (int*)malloc(memSize);
    cudaMalloc((void**) &deviceArray, memSize);

    std::cout << "Before device\n";
    for(int i=0;i<arrayLength;i++)
    {
        hostArray[i] = i+1;
        std::cout << hostArray[i] << "\n";
    }
    std::cout << "\n";

    cudaMemcpy(deviceArray, hostArray, memSize, cudaMemcpyHostToDevice);
    TestDevice <<< 4, 4 >>> (deviceArray);
    cudaMemcpy(hostArray, deviceArray, memSize, cudaMemcpyDeviceToHost);

    std::cout << "After device\n";
    for(int i=0;i<arrayLength;i++)
    {
        std::cout << hostArray[i] << "\n";
    }

    cudaFree(deviceArray);
    free(hostArray);

    std::cout << "Done\n";
}

#endif

MyKernel.cu

#ifndef _MY_KERNEL_
#define _MY_KERNEL_

__global__ void TestDevice(int *deviceArray)
{
    int idx = blockIdx.x*blockDim.x + threadIdx.x;
    deviceArray[idx] = deviceArray[idx]*deviceArray[idx];
}


#endif

Build Log:

1>------ Build started: Project: CUDASandbox, Configuration: Debug x64 ------
1>Compiling with CUDA Build Rule...
1>"C:\CUDA\bin64\nvcc.exe"    -arch sm_10 -ccbin "C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\bin"    -Xcompiler "/EHsc /W3 /nologo /O2 /Zi   /MT  "  -maxrregcount=32  --compile -o "x64\Debug\KernelSupport.cu.obj" "d:\Stuff\Programming\Visual Studio 2008\Projects\CUDASandbox\CUDASandbox\KernelSupport.cu" 
1>KernelSupport.cu
1>tmpxft_000016f4_00000000-3_KernelSupport.cudafe1.gpu
1>tmpxft_000016f4_00000000-8_KernelSupport.cudafe2.gpu
1>tmpxft_000016f4_00000000-3_KernelSupport.cudafe1.cpp
1>tmpxft_000016f4_00000000-12_KernelSupport.ii
1>Linking...
1>KernelSupport.cu.obj : error LNK2005: __device_stub__Z10TestDevicePi already defined in MyKernel.cu.obj
1>KernelSupport.cu.obj : error LNK2005: "void __cdecl TestDevice__entry(int *)" (?TestDevice__entry@@YAXPEAH@Z) already defined in MyKernel.cu.obj
1>D:\Stuff\Programming\Visual Studio 2008\Projects\CUDASandbox\x64\Debug\CUDASandbox.exe : fatal error LNK1169: one or more multiply defined symbols found
1>Build log was saved at "file://d:\Stuff\Programming\Visual Studio 2008\Projects\CUDASandbox\CUDASandbox\x64\Debug\BuildLog.htm"
1>CUDASandbox - 3 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

I am running Visual Studio 2008 on Windows 7 64bit.

---

Edit:

I think I need to elaborate on this a little bit. The end result I am looking for here is to have a normal C++ application with something like Main.cpp with the int main() event and have things run from there. At certains point in my .cpp code I want to be able to reference CUDA bits. So my thinking (and correct me if there a more standard convention here) is that I will put the CUDA Kernel code into their on .cu files, and then have a supporting .cu file that will take care of talking to the device and calling kernel functions and what not.

Answer 1

You are including mykernel.cu in kernelsupport.cu, when you try to link the compiler sees mykernel.cu twice. You’ll have to create a header defining TestDevice and include that instead.

re comment:

Something like this should work

// MyKernel.h
#ifndef mykernel_h
#define mykernel_h
__global__ void TestDevice(int* devicearray);
#endif

and then change the including file to

//KernelSupport.cu
#ifndef _KERNEL_SUPPORT_
#define _KERNEL_SUPPORT_

#include <iostream>
#include <MyKernel.h>
// ...

re your edit

As long as the header you use in c++ code doesn’t have any cuda specific stuff (__kernel__,__global__, etc) you should be fine linking c++ and cuda code.