[Bug ld/31179] New: RISC-V: The SET/ADD/SUB fix breaks ABI compatibility with 2.41 objects

[palmer at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31179

            Bug ID: 31179
           Summary: RISC-V: The SET/ADD/SUB fix breaks ABI compatibility
                    with 2.41 objects
           Product: binutils
           Version: 2.42 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: palmer at gcc dot gnu.org
  Target Milestone: ---

Nelson, David, and Aurelian have been poking this.  There's no bug and
everyone's in different time zones, though, so I'm just starting with something
-- it's a bit rushed, but I wanted to get a big filed so we at least had a
place to talk.

2029e13917d ("RISC-V: Clarify the behaviors of SET/ADD/SUB relocations.") fixes
two bugs.  This was released in 2.41 and those bugs counteract each other, so
an LD with the fix doesn't work with binaries produced with a GAS that doesn't
have the fix.  So this is a defacto user-visible ABI break.

We can tell everyone "just rebuild the old binaries", but since the bug is in a
released version that's a headache for the distros.  The best I can come up
with is to add some tag to the new binaries saying "these don't have the bug",
and then figure it out from there -- that'd have some implications on the LLVM
side of things, I'll poke some folks over there to see what's up.

Unless anyone has a better idea?

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