[libcu++] Dynamically load CUDA library instead of using the runtime (#6899)

* Dynamically load CUDA library instead of using the runtime

* Switch back to windows.h

* Review feedback

* More review feedback

Author: pciolkosz

libcudacxx/include/cuda/__driver/driver_api.h

@@ -28,6 +28,11 @@
 #  include <cuda/std/__internal/namespaces.h>
 #  include <cuda/std/__type_traits/always_false.h>
 #  include <cuda/std/__type_traits/is_same.h>
+#  if _CCCL_OS(WINDOWS)
+#    include <windows.h>
+#  else
+#    include <dlfcn.h>
+#  endif
 
 #  include <cuda.h>
 
@@ -47,21 +52,37 @@ _CCCL_BEGIN_NAMESPACE_CUDA_DRIVER
 _CCCL_SUPPRESS_DEPRECATED_PUSH
 
 //! @brief Gets the cuGetProcAddress function pointer.
-[[nodiscard]] _CCCL_HOST_API inline auto __getProcAddressFn() -> decltype(cuGetProcAddress)*
+[[nodiscard]] _CCCL_PUBLIC_HOST_API inline auto __getProcAddressFn() -> decltype(cuGetProcAddress)*
 {
-  // TODO switch to dlopen of libcuda.so instead of the below
-  void* __fn;
-  ::cudaDriverEntryPointQueryResult __result;
-#  if _CCCL_CTK_AT_LEAST(13, 0)
-  ::cudaError_t __status =
-    ::cudaGetDriverEntryPointByVersion("cuGetProcAddress", &__fn, 13000, ::cudaEnableDefault, &__result);
-#  else
-  ::cudaError_t __status = ::cudaGetDriverEntryPoint("cuGetProcAddress", &__fn, ::cudaEnableDefault, &__result);
-#  endif
-  if (__status != ::cudaSuccess || __result != ::cudaDriverEntryPointSuccess)
+  const char* __fn_name = "cuGetProcAddress_v2";
+#  if _CCCL_OS(WINDOWS)
+  static auto __driver_library = ::LoadLibraryExA("nvcuda.dll", nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
+  if (__driver_library == nullptr)
+  {
+    ::cuda::__throw_cuda_error(::cudaErrorUnknown, "Failed to load nvcuda.dll");
+  }
+  static void* __fn = ::GetProcAddress(__driver_library, __fn_name);
+  if (__fn == nullptr)
+  {
+    ::cuda::__throw_cuda_error(::cudaErrorInitializationError, "Failed to get cuGetProcAddress from nvcuda.dll");
+  }
+#  else // ^^^ _CCCL_OS(WINDOWS) ^^^ / vvv !_CCCL_OS(WINDOWS) vvv
+#    if _CCCL_OS(ANDROID)
+  const char* __driver_library_name = "libcuda.so";
+#    else // ^^^ _CCCL_OS(ANDROID) ^^^ / vvv !_CCCL_OS(ANDROID) vvv
+  const char* __driver_library_name = "libcuda.so.1";
+#    endif // ^^^ !_CCCL_OS(ANDROID) ^^^
+  static void* __driver_library = ::dlopen(__driver_library_name, RTLD_NOW);
+  if (__driver_library == nullptr)
+  {
+    ::cuda::__throw_cuda_error(::cudaErrorUnknown, "Failed to load libcuda.so.1");
+  }
+  static void* __fn = ::dlsym(__driver_library, __fn_name);
+  if (__fn == nullptr)
   {
-    ::cuda::__throw_cuda_error(::cudaErrorUnknown, "Failed to get cuGetProcAddress");
+    ::cuda::__throw_cuda_error(::cudaErrorInitializationError, "Failed to get cuGetProcAddress from libcuda.so.1");
   }
+#  endif // ^^^ !_CCCL_OS(WINDOWS) ^^^
   return reinterpret_cast<decltype(cuGetProcAddress)*>(__fn);
 }
 
@@ -152,7 +173,7 @@ _CCCL_HOST_API inline void __call_driver_fn(Fn __fn, const char* __err_msg, Args
 //! @return The address of the symbol.
 //!
 //! @throws @c cuda::cuda_error if the symbol cannot be obtained or the CUDA driver failed to initialize.
-[[nodiscard]] _CCCL_HOST_API inline void*
+[[nodiscard]] _CCCL_PUBLIC_HOST_API inline void*
 __get_driver_entry_point(const char* __name, [[maybe_unused]] int __major = 12, [[maybe_unused]] int __minor = 0)
 {
   // Get cuGetProcAddress function and call cuInit(0) only on the first call