Linking cuda header to host code

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi, I have copied a small example from dev guide, Parallel vector addition. I have a problem linking them together.

Basically, I have a main.c file, add.h and add.cu files. Main.c initializes program, add.cu contains code to run parallel addition on the device and add.h is a header for add.cu. When I want to include the header to main.c (in order to run the addition), I get a linking error:

When I rename the main.c to main.cu, everything works perfect. What am I missing?

Main.c:

#include <stdio.h>

#include "add.h"

int main() {

	int i;

	int A[4] = { 2, 4, 5, 6 };

	int B[4] = { 1, 2, 3, 4 };

	int C[4];

	VecAdd(A, B, C);

	printf("C = {");

	for(i = 0; i < 4; i++){

		printf("%d,", C[i]);

	}

	printf("}\n");

	return 0;

}

Add.h:

#ifndef ADD_H_

#define ADD_H_

void VecAdd(int *A, int *B, int *C);

#endif

Add.cu:

__global__

void VecAdd_Kernel(int *A, int *B, int *C){

	int i = threadIdx.x;

	C[i] = A[i] + B[i];

}

void VecAdd(int *A, int *B, int *C){

	size_t intSize = sizeof(int);

	int *d_A;

	int *d_B;

	int *d_C;

	cudaMalloc(&d_A, 4*intSize);

	cudaMalloc(&d_B, 4*intSize);

	cudaMalloc(&d_C, 4*intSize);

	cudaMemcpy(d_A, A, 4*intSize, cudaMemcpyHostToDevice);

	cudaMemcpy(d_B, B, 4*intSize, cudaMemcpyHostToDevice);

	VecAdd_Kernel<<<1, 4>>>(d_A, d_B, d_C);

	cudaMemcpy(C, d_C, 4*intSize, cudaMemcpyDeviceToHost);

}

I am on Win 7 32, using Eclipse CDT hacked to use nvcc as a compiler and MS link as linker.

2

.cu files are processed through a C++ frontend, which cause the function name to be decorated. The decorated name then does not match the plain C function name in main.c. The following adjustment should fix this. In Add.h, use

extern “C” void VecAdd(int *A, int *B, int *C);

then add

#include “Add.h”

at the top of Add.cu. That way the compiler is instructed to generate an undecorate, plain C, symbol for VecAdd(). Note that this issue is not specific to CUDA, but is a generic issue that affects all mixed C++ and C builds.

3

I tried that already b4, but when I add this extern “C”, the compiler now returns a syntax error:

Main.h:

#ifndef ADD_H_

#define ADD_H_

extern "C" void VecAdd(int *A, int *B, int *C);

#endif
4

I resolved the problem by wrapping the extern directive in #ifdef:

#ifdef __cplusplus

   extern "C"

#endif

Now it compiles OK