I've added this as Issue 231013.1: https://dwarfstd.org/issues/231013.1.html
-cary On Fri, Oct 13, 2023 at 3:50 PM David Blaikie <dblai...@gmail.com> wrote: > > (derived from: > https://lists.dwarfstd.org/mailman/private/dwarf-workgroup/2023-October/002444.html > ) > > # Tombstoning TU entries in `.debug_names` > > ## Background > > Local type unit entries in `.debug_names` reference type units via their > offset in the `.debug_info` section. > > Assuming a non-DWARF-aware linker, per 6.1.1.3: "When linking object files > containing per-CU indexes, the linker may choose to concatenate the indexes > as ordinary sections ..." > > If a linker does this, it will need to choose what value to resolve a > relocation for the TU offset to, if that TU was discarded. (if the TUs are > bit identical, the linker might resolve all relocations to identical copies > to refer to the remaining copy - but TUs aren't guaranteed to be byte > identical - and since the offsets in the `.debug_names` table refer to > specific byte offset in the TU, these entries can't be used if a > different-but-equivalent copy of the TU is the one that's preserved by the > linker) > > To deal with this, the linker would use a tombstone value of some kind to > indicate that the offset couldn't be resolved. By default, this offset might > be zero - which is a valid offset within the `.debug_info` section, and would > not be possible for the DWARF consumer to differentiate the "ignore this > index entry" from a valid index entry pointing to a TU at offset zero. > > With https://dwarfstd.org/issues/200609.1.html we chose a tombstone value for > other cases (.debug_info referencing into code - in the case of discarded > functions) of "the largest representable value". This seems like a good > foundation for addressing this new, similar case. > > ## Proposed Changes > > Add a paragraph between the first and second/last in 6.1.1.4.3 that reads: > > "Any local TU entry with a maximum representable value is considered not > present. Any index entry referencing such a local TU entry should be ignored." -- Dwarf-discuss mailing list Dwarf-discuss@lists.dwarfstd.org https://lists.dwarfstd.org/mailman/listinfo/dwarf-discuss
