[Pre-RFC] BTF relocations

re: "relocatable". I would definitely not call it "bpf_relocatable" (target specific), but between "relocatable" and "btf_relocatable", BTF is the means through which relocation information is captured (BTF types/fields) and expressed (.BTF.ext section), so btf_ prefix seems appropriate. For this Swift use case you were talking about, would relocation information be expressed differently somehow?

In the end it doesn't matter all that much, but too-generic "relocatable" has a potential to be, well, too generic and thus confusing. But just my 2 cents.

re: instrinsics, make sense and seems like a good idea. will the "does it exist" primitive be expressed as an extra argument to "preserve_xxx_info" or it would require its own set of intrinsics?