OpenCL and OpenGL interop extension not working (clGetGLContextInfoKHR crash) - opengl

Question

I'm struggling with getting GL+CL to work together.
I've been following this tutorial. In my code I first call clGetPlatformIDs and retrieve the first (and only) platform. I also get my gl_context from SDL2. Then I want to query the device used by OpenGL with help of clGetGLContextInfoKHR. I successfully obtain this function with clGetExtensionFunctionAddressForPlatform(platform_id, "clGetGLContextInfoKHR") but unfortunately when I call it, I get a segmentation fault. My code is written in Rust but I use low level OpenCL binding, so it looks almost like its C counterpart.
pub fn new(gl_context: &GLContext) -> Result<Self, ClGlError> {
println!("Initialising OpenCL context");
let raw = unsafe { gl_context.raw() };
println!("Getting default opencl platform");
let platform_id = Self::default_platform()?; // this is valid and not null
let mut props:[cl_sys::cl_context_properties;5] = [
//OpenCL platform
cl_sys::CL_CONTEXT_PLATFORM as cl_sys::cl_context_properties, platform_id as cl_sys::cl_context_properties,
//OpenGL context
cl_sys::CL_GL_CONTEXT_KHR, raw as cl_sys::cl_context_properties,
0
];
let mut device: cl_device_id = std::ptr::null_mut();
let p: *mut cl_device_id = (&mut device) as *mut cl_device_id;
let fn_name = b"clGetGLContextInfoKHR\0" as *const u8 as *const i8;
println!("Getting clGetGLContextInfoKHR");
let clGetGLContextInfoKHR = unsafe{clGetExtensionFunctionAddressForPlatform(platform_id, fn_name ) as cl_sys::clGetGLContextInfoKHR_fn};
if clGetGLContextInfoKHR.is_null(){
// error handling here
}
println!("Getting device"); // this is the last thing I see before segfault
unsafe{
(*clGetGLContextInfoKHR)(props.as_mut_ptr(),cl_sys::CL_CURRENT_DEVICE_FOR_GL_CONTEXT_KHR,std::mem::size_of::<cl_device_id>(),device as *mut c_void,std::ptr::null_mut());
}
panic!("All good") // this is never reached
}
I have a fairly new Graphics card which supports cl_khr_gl_sharing.
Here is clinfo
Number of platforms 1
Platform Name NVIDIA CUDA
Platform Vendor NVIDIA Corporation
Platform Version OpenCL 1.2 CUDA 11.2.162
Platform Profile FULL_PROFILE
Platform Extensions cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_fp64 cl_khr_byte_addressable_store cl_khr_icd cl_khr_gl_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unroll cl_nv_copy_opts cl_nv_create_buffer cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_device_uuid
Platform Extensions function suffix NV
Platform Name NVIDIA CUDA
Number of devices 1
Device Name GeForce GTX 960
Device Vendor NVIDIA Corporation
Device Vendor ID 0x10de
Device Version OpenCL 1.2 CUDA
Driver Version 460.80
Device OpenCL C Version OpenCL C 1.2
Device Type GPU
Device Extensions cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_fp64 cl_khr_byte_addressable_store cl_khr_icd cl_khr_gl_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unroll cl_nv_copy_opts cl_nv_create_buffer cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_device_uuid
Perhaps the most important clue might be that I tried a bunch of other libraries that build on top of opencl and in all of them, whenever I called clGetGLContextInfoKHR (wrapped in safer and higher-level API) it crashed. I think it's very unlikely that all those libraries had bugs in their code, so probably it's some problem in my environment. However, as you can see, my graphics card clearly supports all necessary extensions.

Answer 1

I am not sure why clGetGLContextInfoKHR is failing but I figured out that it's not really necesary to call it.
Instead you may just use this on Linux
cl_context_properties properties[] = {
CL_GL_CONTEXT_KHR, (cl_context_properties) glXGetCurrentContext(),
CL_GLX_DISPLAY_KHR, (cl_context_properties) glXGetCurrentDisplay(),
CL_CONTEXT_PLATFORM, (cl_context_properties) platform,
0
};
this on Windows
cl_context_properties properties[] = {
CL_GL_CONTEXT_KHR, (cl_context_properties) wglGetCurrentContext(),
CL_WGL_HDC_KHR, (cl_context_properties) wglGetCurrentDC(),
CL_CONTEXT_PLATFORM, (cl_context_properties) platform,
0
};
or this on OS X
CGLContextObj glContext = CGLGetCurrentContext();
CGLShareGroupObj shareGroup = CGLGetShareGroup(glContext);
cl_context_properties properties[] = {
CL_CONTEXT_PROPERTY_USE_CGL_SHAREGROUP_APPLE,
(cl_context_properties)shareGroup,
0
};
More info can be found in the book
OpenCL in Action: How to Accelerate Graphics and Computations