HIP object code metadata can appear as a dedicated data section in AMDGPU/HIP/ROCm ELF files or a separate file with .dat or .bin extension or with no extension. They act as precompiled headers or reflective metadata in a format that AMD's GPU drivers and ROCm toolchain can parse so multiple shaders using the same graphics API from one application can run correctly without conflicts.
Technically, they are MessagePack (.msgpack) files or in MessagePack format - the same format as Flax models. Think of it as binary JSON. They are usually serialized objects with a solutions or amdhsa.kernels header.