https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82005
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- That is, looking for documentation on Mach-O I find in mach-o/reloc.h * Another type of generic relocation, GENERIC_RELOC_SECTDIFF, is to support * the difference of two symbols defined in different sections. That is the * expression "symbol1 - symbol2 + constant" is a relocatable expression when * both symbols are defined in some section. For this type of relocation the * both relocations entries are scattered relocation entries. The value of * symbol1 is stored in the first relocation entry's r_value field and the * value of symbol2 is stored in the pair's r_value field. which I thought would apply here. Looks like this doesn't work for UNDEFs for some weird reason? Note all of these relocations are resolvable by the link editor.
