Disassemble an OpenCL kernel?

Question

I'm not sure if it's possible. I want to study OpenCL in-depth, so I was wondering if there is a tool to disassemble an compiled OpenCL kernel.

For normal x86 executable, I can use objdump to get a disassembly view. Is there a similar tool for OpenCL kernel, yet?

Answer 1

If you're using NVIDIA's OpenCL implementation for their GPUs, you can do the followings to disassemble an OpenCL kernel:

1. Use clGetEventProfilingInfo() to dump the ptx code to a file, say ptxfile.ptx. Please refer to the OpenCL specification to have more details on this function.

2. Use nvcc to compile ptx to cubin file, for example: nvcc -cubin -arch=sm_20 ptxfile.ptx will compile ptxfile.ptx onto a compute capability 2.0 device.

3. Use cuobjdump to disassemble the cubin file into GPU instructions. For example: cuobjdump -sass ptxfile.cubin

Hope this helps.

Answer 2

The simplest solution, in my experience, is to use clangs OpenCL C compiler and emit SPIR. It even works on Godbolt's compiler explorer: https://godbolt.org/z/_JbXPb

Clang can also emit ptx (https://godbolt.org/z/4ARMqM) and amdhsa (https://godbolt.org/z/TduTZQ), but it may not correspond to the ptx and amdhsa assembly generated by the respective driver at runtime.

Answer 3

I know that this is an old question, but in case someone comes looking here for disassembling a AMD GPU kernel, you can do the following in linux:

export GPU_DUMP_DEVICE_KERNEL=3

This make any kernel that is compiled on your machine dump the assembled code to a file in the same directory.

Source: http://dis.unal.edu.co/~gjhernandezp/TOS/GPU/ATI_Stream_SDK_OpenCL_Programming_Guide.pdf

Sections 4.2.1 and 4.2.2