Very weird Vulkan problem likely nobody else would ever encounter: way back in the day Mesa wrongly installed ICD definitions for i386 too on amd64, e.g. $PREFIX/share/vulkan/icd.d/radeon_icd.i386.json. I’ve installed Mesa manually, and never cleaned them up, so I’ve had these files with last modified date in 2017. They didn’t really cause any problems (well, other than duplicating the GPU in device lists)… until I ran the Vulkano test suite which would run GetPhysicalDeviceFeatures2 on all devices. For whatever reason, it would get a null pointer for that function on the second (described-by-i386-file) device and explode.

Wow, interesting github thread: Mesa planning to reuse existing SPIR-V infrastructure to run OpenCL!