Undefined reference to __hxdGetDeviceFunc

Accelerated Computing HPC Compilers nvc, nvc++ and nvfortran
1

Hi,

The code below attempts to access heap-allocated memory via a std::shared_ptr, within the body of the value-capturing lambda function given to std::transform.

#include <memory>
#include <execution>
#include <algorithm>

int main(int argc, char *argv[])
{
  using namespace std;
  const unsigned sz{1024};
  shared_ptr<int> nine{new int{9}};
  vector<unsigned> v(sz);

  const auto pol = execution::par_unseq;  
  transform(pol, v.begin(), v.end(), v.begin(), [=](auto) { return *nine; });

  return 0;
}

Compiling with nvc++ fails with the following message:

nvlink error   : Undefined reference to '__hxdGetDeviceFunc' in '/tmp/nvc++pDvdTPsfRv7O.o'
pgacclnk: child process exit status 2: /opt/nvidia/hpc_sdk_multi/Linux_x86_64/20.11/compilers/bin/tools/nvdd

The compile command is nvc++ -stdpar -std=c++17 prog.cpp. I’m using the HPC SDK 20.11 and CUDA 11.0 under 64-bit Ubuntu 20.10. I think it’s a bug, but as we plan to use std::shared_ptr in this way, I wanted to double-check.

Cheers,
Paul

2

Thanks Paul. I’ve added an issue report, TPR #29384, and will have our engineers investigate.

-Mat

1 Like
3

Looks like this is fixed in 21.1 and 21.2. Thanks!
Paul

4

Hi Paul,

Odd, I still show this one failing. Unclear why it’s working for you now.

% nvc++ test.cpp -stdpar -V21.2
nvlink error   : Undefined reference to '__hxdGetDeviceFunc' in '/tmp/nvc++jJYsdBRVlPIMy.o'

Mat

5

My mistake…I’d forgotten the -stdpar flag.

6

More info on this. std::shared_ptr uses virtual functions in its implementation. Virtual functions are implemented with pointers to functions, which nvc++ -stdpar does not currently support in device code. That unfortunately makes std::shared_ptr unusable in device code.

In the near term, we’ll work on improving the error message so it’s more evident as to the issue. Long term, we are working on support for function pointers and virtual functions, but this requires some support in the CUDA driver so will be awhile.

1 Like
7

Thanks Mat, that makes sense.
Paul

8

As Mat said, now in 21.3 you will see this error:
NVC+±S-0800-The function pointer is not allowed in the GPU Execution code.

1 Like