[Pre-RFC] BTF relocations

A few questions:

• Can a relocation affect whether two fields overlap (e.g. if a struct changes to a union)?
• Can a relocation change an array index?
• Can a relocation affect the number of pointer dereferences necessary to access a field?
• Is it ever possible to construct one of these structs? Or does the potential for additional fields Rust doesn't know about mean construction must be forbidden?
• Do we need an analogue of #[link_name] for struct and field names?
• What is the failure mode like? If you make a mistake or run on an unsupported kernel version, and the relocations aren't sufficient to make offets or types line up, is the verifier guaranteed to reject the program?
• Is there any connection to/similarity with Swift stable ABI?