Question

I’ve a file A.cu containing function void A(). I’ve another file test_A.c which calls the cuda function A() and also has function declaration as

extern void A();

Now I compile and link them as follows

nvcc -c -o A.o A.cu 
gcc -o test_A test_A.c A.o /opt/cuda-4.0/cuda/lib64/libcudart.so

and I get error like

undefined reference to `A'

What am I missing?

Answer 1

The problem is probably C++ name mangling. CUDA code is compiled with a C++ compiler, not a C compiler. If you dump the contents of A.o you should find a symbol called something like _Z1Av, rather than A as the C compiler is expecting.

To overcome this, you can use the following declaration inside your A.cu file:

extern "C" void A(void)
{
    .......
}

This will tell the C++ compiler to use C conventions when compiling the code, and a suitably named function will be written to the object file A.o which the C compiler and linker can understand.