Re: [PATCH] xtensa: add R_XTENSA_PDIFF_ULEB128 for DWARF uleb128 diffs

Hi Alexey,

this patch does not apply to the current matser, what version
of binutils is it against?
It's also not in a plain text format...

On Mon, Aug 3, 2026 at 4:38 AM Alexey Lapshin
<[email protected]> wrote:
>
> DWARF 5 location and range lists encode many same-section symbol
> differences as uleb128.  Today the assembler must mark all covered code
> no_transform so linker relaxation cannot change those differences, which
> effectively disables relaxation for nearly every function that has DWARF 5
> debug info.
>
> Emit R_XTENSA_PDIFF_ULEB128 instead: like R_XTENSA_PDIFF32 the difference
> stays in the section contents and the reloc records the subtracted symbol,
> but the assembler pads the uleb128 to a fixed width (minimal encoding plus
> one spare byte) and the linker rewrites the value in place after
> relaxation.
>
> sleb128 and cross-section differences still fall back to no_transform.
> Growth that needs more than the reserved spare byte is reported as a
> relocation overflow.
>
> bfd/
>         * bfd-in2.h: Regenerated.
>         * elf32-xtensa.c (elf_howto_table): New entry for
>         R_XTENSA_PDIFF_ULEB128.
>         (elf_xtensa_reloc_type_lookup, elf_xtensa_do_reloc): Handle it.
>         (relax_section): Rewrite padded uleb128 differences in place.
>         * libbfd.h (bfd_reloc_code_real_names): Add
>         BFD_RELOC_XTENSA_PDIFF_ULEB128.
>         * reloc.c: Document BFD_RELOC_XTENSA_PDIFF_ULEB128.
>
> binutils/
>         * readelf.c (is_none_reloc): Recognize R_XTENSA_PDIFF_ULEB128.
>
> gas/
>         * write.c (cvt_frag_to_fill): Pad leb128 frags to the reserved
>         size when md_leb128_frag_size grew them.
>         (relax_segment): Call md_leb128_frag_size if defined.
>         * config/tc-xtensa.h (xtensa_symfield_type): Add
>         has_leb128_diff_reloc.
>         (md_leb128_frag_size): Define.
>         * config/tc-xtensa.c (xtensa_md_finish): Insert uleb128 fixes.
>         (xtensa_insert_uleb128_fixes, xtensa_leb128_frag_size): New.
>         (xtensa_mark_difference_of_two_symbols): Skip relocated diffs.
>         (md_apply_fix): Ignore BFD_RELOC_XTENSA_PDIFF_ULEB128.
>         * testsuite/gas/xtensa/pdiff-uleb128.s: New test.
>         * testsuite/gas/xtensa/pdiff-uleb128.d: New test.
>         * testsuite/gas/xtensa/pdiff-uleb128-norelax.d: New test.
>
> include/
>         * elf/xtensa.h (elf_xtensa_reloc_type): Add
>         R_XTENSA_PDIFF_ULEB128.
>
> ld/
>         * testsuite/ld-xtensa/relax-uleb128.s: New test.
>         * testsuite/ld-xtensa/relax-uleb128.d: New test.
>         * testsuite/ld-xtensa/relax-uleb128-2.s: New test.
>         * testsuite/ld-xtensa/relax-uleb128-2.d: New test.
>         * testsuite/ld-xtensa/xtensa.exp: Run them.
> ---
>  bfd/bfd-in2.h                                 | 10 +++
>  bfd/elf32-xtensa.c                            | 80 +++++++++++++++++
>  bfd/libbfd.h                                  |  1 +
>  bfd/reloc.c                                   | 12 +++
>  binutils/readelf.c                            |  3 +-
>  gas/config/tc-xtensa.c                        | 86 ++++++++++++++++++-
>  gas/config/tc-xtensa.h                        |  5 ++
>  .../gas/xtensa/pdiff-uleb128-norelax.d        | 20 +++++
>  gas/testsuite/gas/xtensa/pdiff-uleb128.d      | 12 +++
>  gas/testsuite/gas/xtensa/pdiff-uleb128.s      |  7 ++
>  gas/write.c                                   | 20 +++++
>  include/elf/xtensa.h                          |  3 +
>  ld/testsuite/ld-xtensa/relax-uleb128-2.d      | 12 +++
>  ld/testsuite/ld-xtensa/relax-uleb128-2.s      | 18 ++++
>  ld/testsuite/ld-xtensa/relax-uleb128.d        | 11 +++
>  ld/testsuite/ld-xtensa/relax-uleb128.s        | 16 ++++
>  ld/testsuite/ld-xtensa/xtensa.exp             |  2 +
>  17 files changed, 314 insertions(+), 4 deletions(-)
>  create mode 100644 gas/testsuite/gas/xtensa/pdiff-uleb128-norelax.d
>  create mode 100644 gas/testsuite/gas/xtensa/pdiff-uleb128.d
>  create mode 100644 gas/testsuite/gas/xtensa/pdiff-uleb128.s
>  create mode 100644 ld/testsuite/ld-xtensa/relax-uleb128-2.d
>  create mode 100644 ld/testsuite/ld-xtensa/relax-uleb128-2.s
>  create mode 100644 ld/testsuite/ld-xtensa/relax-uleb128.d
>  create mode 100644 ld/testsuite/ld-xtensa/relax-uleb128.s

-- 
Thanks.
-- Max