Orbital: A PlayStation 4 Emulator That Is Emulating The PS4's AMD GPU Using Vulkan
Orbital leverages QEMU and other open-source components. At this stage it's not running any PS4 games but is able to boot into safe mode on PS4 5.xx kernels.
The graphics support is achieved by fully emulating the PS4's AMD Sea Islands graphics processor using Vulkan and then dynamically recompiling GCN bytecode into SPIR-V so that common IR can then be sent into the Vulkan driver of the host system. With this setup, they are able to see graphics outputs including PS4 error messages:
Orbital is currently being worked on for Windows, macOS, and Linux. The system requirements will be hefty with already requiring AVX2 capable CPUs and 12GB of RAM.
Of course, it doesn't have the blessing of Sony but if you are interested in diving into the code -- it's not anything usable for gamers yet nor likely for quite some time -- and learning more about their emulating of Radeon GPUs using Vulkan/SPIR-V, the project is hosted on GitHub where they also have a roadmap.