This project adds a GPU model to simulate graphics and GPGPU apps under gem5 (http://www.gem5.org/Running_gem5#Full_System_.28FS.29_Mode).
Beside gem5, we several tools: gpgpu-sim, gem5-gpu and Mesa 3D.
Instructions are available here (Last update: Aug-12 2019, more updates will be pushed end of Sept/Oct).