问题描述
我正在尝试用UIDntu上的openCL程序编译一个之前工作过一次的NVIDIA卡，
#include <CL/cl.h>
#include <iostream>
#include <vector>
using namespace std;
int main() {
cl_platform_id platform;
cl_device_id device;
cl_context context;
cl_command_queue command_queue;
cl_int error;
if(clGetPlatformIDs(1, &platform, NULL) != CL_SUCCESS) {
cout << "platform error" << endl;
}
if(clGetDeviceIDs(platform, CL_DEVICE_TYPE_GPU, 1, &device, NULL) != CL_SUCCESS) {
cout << "device error" << endl;
}
context = clCreateContext(NULL, 1, &device, NULL, NULL, &error);
if(error != CL_SUCCESS) {
cout << "context error" << endl;
}
command_queue = clCreateCommandQueue(context, device, 0, &error);
if(error != CL_SUCCESS) {
cout << "command queue error" << endl;
}
return 0;
}
我像这样编译它，
g++ -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL opencl.cpp
我得到了这个结果
/tmp/ccAdS9ig.o: In function `main':
opencl.cpp:(.text+0x1a): undefined reference to `clGetPlatformIDs'
opencl.cpp:(.text+0x3d): undefined reference to `clGetDeviceIDs'
opencl.cpp:(.text+0x65): undefined reference to `clCreateContext'
opencl.cpp:(.text+0x85): undefined reference to `clCreateCommandQueue'
collect2: ld returned 1 exit status
但是nm -D /usr/lib/nvidia-current/libOpenCL.so告诉我libOpenCL.so至少包含clGetPlatformIDs
0000000000002400 T clGetKernelWorkGroupInfo
0000000000002140 T clGetMemObjectInfo
0000000000002e80 T clGetPlatformIDs
0000000000002de0 T clGetPlatformInfo
0000000000002310 T clGetProgramBuildInfo
00000000000022f0 T clGetProgramInfo
00000000000021f0 T clGetSamplerInfo
我错过了什么。
最佳解决方法
从gcc手册页：
-llibrary
-l library
Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o
-lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded.
The linker searches a standard list of directories for the library, which is actually a file named liblibrary.a. The linker then uses this file as if it had been specified
precisely by name.
因此，请尝试在编译命令中的file参数后指定-lOpenCL。
您还可以在libOpenCL.so中搜索符号，这是一个共享库文件。使用您的命令，您可以再次将程序链接到静态库，格式为libOpenCL.a。
次佳解决方法
当您进行链接时，库和源文件的顺序会有所不同。例如，对于你的情况，
g++ -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL opencl.cpp
可能无法加载OpenCL库中定义的函数，因为在它们要求look-up之前没有任何内容。但是，如果你使用，
g++ opencl.cpp -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL
然后在OpenCL库中找到任何函数请求，它们将被加载。