On Thu, 25 Feb 2021, Jiaxun Yang wrote: > > You may want to use composed relocations to refer to .LA1 (R_MIPS_32) and > > .LA0 (R_MIPS_SUB). There may or may not be linker updates needed; unlike > > the RISC-V one the MIPS BFD backend already supports composed relocations > > with the usual ELF gABI semantics. It would be good to switch to RELA at > > this point universally too; none of new stuff will work with old linkers > > anyway. > > Thanks for your hint;-) > > I'm unsure about how should we express composed relocations in assembly :-/ Just like we already do; R_MIPS_SUB could be easily produced directly from the `-' operator. I note too that $pc is effectively used twice in the calculation, cancelling itself, so I think we can do better, though it seems to me the original semantics of %pcrel_hi/%pcrel_lo pseudo-ops wasn't thought well (I guess it was just blindly copied from %hi/%lo by adding PC-relative interpretation with no further thinking as to whether it is usable in reality). It seems to me that we could overload the semantics of these pseudo-ops in a compatible manner though. Also are you concerned about linker relaxation you're possibly working on here? I'm asking because a calculation like (.LA1 - .LA0) works out as an assembly constant normally, so it's not a concern really. And as I recall existing MIPS linker relaxation does not rely on label symbols anyway (and is probably not defined for plain R6 anyway as I reckon there is nothing to relax at the link stage for that ISA). Where it might start to matter is the microMIPS ISA however; offhand I don't remember what exactly it looks like at R6 though. > MIPS N32/N64 ABI is already using RELA, do you mean switch to RELA for o32 > as well? Yes, with "universally" I meant: "across all the ABIs". Maciej
