Linking .CU and .CPP files

Accelerated Computing CUDA CUDA Programming and Performance
1

Hello Guys,

I have been working with CUDA files for a while, and now I need to use them in .CPP files. Can anyone tell me the proper procedure to compile and link the .CU and .CPP files? I have seen several posts online that suggest extern “C” for functions that call CUDA kernels. The extern “C” functions and the CUDA kernel reside inside the .CU file. While I am able to generate object files, but when I link them, it gives me the error “undefined reference to ” where is the extern “C” function (residing inside .CU file) that calls the CUDA kernel. I am terribly stuck and will really appreciate if you can get me out of it External Image

Here is what I have been doing

bash $: g++ -c -I $(LIBRARIES) main.cpp
bash $: nvcc -c -I $(LIBRARIES) gpu.cu
bash $: nvcc -o gpuexec main.o gpu.o (also tried g++ but gives the same error)
bash $: main.o: In function ‘main’:
main.cpp:(.text+0x33c9): undefined reference to ‘gpucaller’
collect2: ld returned 1 exit status
make: *** …

‘gpucaller’ is the extern “C” function residing inside a the gpu.cu file. It calls the CUDA kernel global void mykernel…

Help guys!

Thanks,

Vivek

2

Check the names in both object files:

nm gpu.o |grep -y gpucaller
nm main.o |grep -y gpucaller

3

In gpu.o it is: 0000000000000000 T myprint
In main.o it is: U myprint

4

Actually I was playing around and changed the name of gpucaller to myprint.

5

You need to put both the kernel function (global) and the code that invokes it into the same source file. You can either create a thin wrapper (host-side function callKernel that will simply pass all the input to GPU kernel) or use #include to include the cu file into each CPP file. Note that if you use #include you do not need to pass the cu file to compiler and linker.

6

I am having the same problem even when I am not creating a kernel function. I have the files main.c, function.cu, and function.cuh as below

//main.c

#include <stdio.h>

#include <stdlib.h>

#include "function.cuh"

int main()

{

	float f1,f2,f3;

	

	f1 = 2;

	f2 = 4;

	f3 = add(f1,f2);

	printf("\n%f\n\n",f3);

	return 0;

}

//function.cu

#include <stdio.h>

#include <stdlib.h>

float add(float f1, float f2)

{

	float f3;

	f3 = f1 + f2;

	return f3;

}

//function.cuh

#ifndef FUNCTION_H

#define FUNCTION_H

float add(float f1, float f2);

#endif

When I compile and link I get the following:

$ gcc -c main.c

$ nvcc -c function.cu

$ gcc -o test main.o function.o -L/usr/local/cuda/lib64 -lcudart

main.o: In function `main’:

main.c:(.text+0x2c): undefined reference to `add’

collect2: ld returned 1 exit status

Seems like the same problem, any ideas?

7

I am having the same problem even when I am not creating a kernel function. I have the files main.c, function.cu, and function.cuh as below

//main.c

#include <stdio.h>

#include <stdlib.h>

#include "function.cuh"

int main()

{

	float f1,f2,f3;

	

	f1 = 2;

	f2 = 4;

	f3 = add(f1,f2);

	printf("\n%f\n\n",f3);

	return 0;

}

//function.cu

#include <stdio.h>

#include <stdlib.h>

float add(float f1, float f2)

{

	float f3;

	f3 = f1 + f2;

	return f3;

}

//function.cuh

#ifndef FUNCTION_H

#define FUNCTION_H

float add(float f1, float f2);

#endif

When I compile and link I get the following:

$ gcc -c main.c

$ nvcc -c function.cu

$ gcc -o test main.o function.o -L/usr/local/cuda/lib64 -lcudart

main.o: In function `main’:

main.c:(.text+0x2c): undefined reference to `add’

collect2: ld returned 1 exit status

Seems like the same problem, any ideas?

8

My first guess would be calling conventions - cu files are also compiled with C++ compiler. Add “extern “C”” to add function declaration.

9

My first guess would be calling conventions - cu files are also compiled with C++ compiler. Add “extern “C”” to add function declaration.

10

Thanks that worked! Also worked when I put the main function in the .cu file and the add function in the .cpp file (obviously had to switch from using .c file to .cpp file).

I appreciate the help
-David

11

Thanks that worked! Also worked when I put the main function in the .cu file and the add function in the .cpp file (obviously had to switch from using .c file to .cpp file).

I appreciate the help
-David

12

i have the same error. I created a shared library wich use cublas but at moment of linking with file the main.c I get the “undefined reference” error with the function of shared library.

So the problem is that the main function have be in a *.cu file ?¿?¿