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

[nelsonc1225 at sourceware dot org]

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

Nelson Chu <nelsonc1225 at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #12 from Nelson Chu <nelsonc1225 at sourceware dot org> ---
commit 73d931e560059a87d76f528fafbb4270a98746bc
Refs: gdb-14-branchpoint-932-g73d931e5600
Author:     Nelson Chu <nelson@rivosinc.com>
AuthorDate: Wed Dec 20 10:37:41 2023 +0800
Commit:     Nelson Chu <nelson@rivosinc.com>
CommitDate: Thu Dec 28 14:51:50 2023 +0800

    RISC-V: PR31179, The SET/ADD/SUB fix breaks ABI compatibility with 2.41
objects

    * Problematic fix commit,
    2029e13917d53d2289d3ebb390c4f40bd2112d21
    RISC-V: Clarify the behaviors of SET/ADD/SUB relocations

    * Bugzilla,
    https://sourceware.org/bugzilla/show_bug.cgi?id=31179#c5

    The addend of SUB_ULEB128 should be zero if using .uleb128, but we make it
    non-zero by accident in assembler before.  This causes troubles by applying
    the above commit, since the calculation is changed to support .reloc *SUB*
    relocations with non-zero addend.

    We encourage people to rebuild their stuff to get the non-zero addend of
    SUB_ULEB128, but that might need some times, so report warnings to inform
    people need to rebuild their stuff if --check-uleb128 is enabled.

    Since the failed .reloc cases for ADD/SET/SUB/ULEB128 are rarely to use,
    it may acceptable that stop supproting them until people rebuld their
stuff,
    maybe half-year or a year later.  Or maybe we should teach people that
don't
    write the .reloc R_RISCV_SUB* with non-zero constant, and then report
    warnings/errors in assembler.

    bfd/
            * elfnn-riscv.c (perform_relocation): Ignore the non-zero addend of
            R_RISCV_SUB_ULEB128.
            (riscv_elf_relocate_section): Report warnings to inform people need
            to rebuild their stuff if --check-uleb128 is enabled.  So that can
            get the right non-zero addend of R_RISCV_SUB_ULEB128.
            * elfxx-riscv.h (struct riscv_elf_params): Added bool
check_uleb128.
    ld/
            * NEWS: Updated.
            * emultempl/riscvelf.em: Added linker risc-v target options,
            --[no-]check-uleb128, to enable/disable checking if the addend of
            uleb128 is non-zero or not.  So that people will know they need to
            rebuild the objects with binutils 2.42 and up, to get the right
zero
            addend of SUB_ULEB128 relocation, or they may get troubles if using
            .reloc.
            * ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
            * ld/testsuite/ld-riscv-elf/pr31179*: New test cases.

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