Re: [PATCH] bfd: xtensa: keep property tables without linker script KEEP

Hi Alexey,

On Tue, Aug 11, 2026 at 11:12 AM Alexey Lapshin
<[email protected]> wrote:
>
> Property sections are unreferenced, so linker scripts kept them alive
> with KEEP(). That does keep the tables, but it also keeps dead code:
> gas puts .xt.prop/.xt.lit for a COMDAT function into that function's
> group, and _bfd_elf_gc_mark marks every member of a group when one
> member is marked. KEEP() on the property section therefore retains the
> code, literals, rodata and exception tables of unused C++ template
> instantiations and inline functions, bloating the final image. Dropping
> KEEP() instead loses the property tables of live code, because
> non-COMDAT objects share one .xt.prop that nothing references.
>
> Mark property tables from the gc_mark_extra_sections hook, once the
> sections they describe have been marked, using the existing
> xtensa_get_property_section lookup. Set gc_mark directly rather than
> calling _bfd_elf_gc_mark, so a property section that belongs to a COMDAT
> group does not drag in the rest of the group. Linker scripts no longer
> need KEEP() for .xt.prop/.xt.lit. Warn once if KEEP is still used for a
> property section base name.
>
> bfd/
>         * elf32-xtensa.c (elf_xtensa_gc_mark_extra_sections): New
>         function. Warn if KEEP is used for a property section.
>         (elf_backend_gc_mark_extra_sections): Define.
>         (elf_xtensa_gc_mark_hook): Update comment.
>
> include/
>         * elf/xtensa.h (XTENSA_PROPERTY_SEC_NAMES): New macro.
>
> ld/
>         * testsuite/ld-xtensa/gc-prop.d: New test.
>         * testsuite/ld-xtensa/gc-prop.map: New test map check.
>         * testsuite/ld-xtensa/gc-prop.s: New test source.
>         * testsuite/ld-xtensa/gc-prop.t: New test script.
>         * testsuite/ld-xtensa/xtensa.exp: Run it.
> ---
>  bfd/elf32-xtensa.c                 | 76 ++++++++++++++++++++++++++----
>  include/elf/xtensa.h               |  3 ++
>  ld/testsuite/ld-xtensa/gc-prop.d   |  7 +++
>  ld/testsuite/ld-xtensa/gc-prop.map |  9 ++++
>  ld/testsuite/ld-xtensa/gc-prop.s   |  9 ++++
>  ld/testsuite/ld-xtensa/gc-prop.t   |  7 +++
>  ld/testsuite/ld-xtensa/xtensa.exp  |  1 +
>  7 files changed, 102 insertions(+), 10 deletions(-)
>  create mode 100644 ld/testsuite/ld-xtensa/gc-prop.d
>  create mode 100644 ld/testsuite/ld-xtensa/gc-prop.map
>  create mode 100644 ld/testsuite/ld-xtensa/gc-prop.s
>  create mode 100644 ld/testsuite/ld-xtensa/gc-prop.t

Please resend it in a plain text form against the binutils master.

> diff --git a/bfd/elf32-xtensa.c b/bfd/elf32-xtensa.c
> index eb7fef9331e..2eaaee409b2 100644
> --- a/bfd/elf32-xtensa.c
> +++ b/bfd/elf32-xtensa.c
> @@ -1328,16 +1328,12 @@ elf_xtensa_gc_mark_hook (asection *sec,
>                          struct elf_link_hash_entry *h,
>                          Elf_Internal_Sym *sym)
>  {
> -  /* Property sections are marked "KEEP" in the linker scripts, but they
> -     should not cause other sections to be marked.  (This approach relies
> -     on elf_xtensa_discard_info to remove property table entries that
> -     describe discarded sections.  Alternatively, it might be more
> -     efficient to avoid using "KEEP" in the linker scripts and instead use
> -     the gc_mark_extra_sections hook to mark only the property sections
> -     that describe marked sections.  That alternative does not work well
> -     with the current property table sections, which do not correspond
> -     one-to-one with the sections they describe, but that should be fixed
> -     someday.) */
> +  /* Nothing refers to a property section, so it is kept alive by
> +     elf_xtensa_gc_mark_extra_sections instead, and its relocations must
> +     not cause other sections to be marked.  (This relies on
> +     elf_xtensa_discard_info to remove property table entries that
> +     describe discarded sections, which is needed anyway because a
> +     property section may describe more than one section.)  */
>    if (xtensa_is_property_section (sec))
>      return NULL;
>
> @@ -1353,6 +1349,65 @@ elf_xtensa_gc_mark_hook (asection *sec,
>  }
>
>
> +/* Property sections are not referenced by anything, so this pass marks
> +   the ones describing sections that have been marked.  */
> +
> +static bool
> +elf_xtensa_gc_mark_extra_sections (struct bfd_link_info *info,
> +                                  elf_gc_mark_hook_fn gc_mark_hook)
> +{
> +  static const char *const prop_names[] = XTENSA_PROPERTY_SEC_NAMES;
> +  bfd *sub;
> +  bool warned = false;
> +
> +  _bfd_elf_gc_mark_extra_sections (info, gc_mark_hook);
> +
> +  for (sub = info->input_bfds; sub != NULL; sub = sub->link.next)
> +    {
> +      asection *sec;
> +
> +      if (!is_xtensa_elf (sub))
> +       continue;
> +
> +      for (sec = sub->sections; sec != NULL; sec = sec->next)
> +       {
> +         size_t i;
> +
> +         if (!sec->gc_mark
> +             || (sec->flags & SEC_ALLOC) == 0
> +             || xtensa_is_property_section (sec))
> +           continue;
> +
> +         for (i = 0; i < sizeof (prop_names) / sizeof (prop_names[0]); i++)
> +           {
> +             asection *prop_sec =
> +               xtensa_get_property_section (sec, prop_names[i]);
> +
> +             /* Set "gc_mark" directly rather than calling _bfd_elf_gc_mark:
> +                a property section can be a member of the COMDAT group of
> +                the section it describes, and marking a group member retains
> +                the entire group.  Nothing else needs to be marked because
> +                elf_xtensa_gc_mark_hook ignores relocations in property
> +                sections.  */
> +             if (prop_sec != NULL)
> +               {
> +                 if (!warned && (prop_sec->flags & SEC_KEEP) != 0)
> +                   {
> +                     info->callbacks->einfo
> +                       (_("%P: warning: KEEP should not be used for Xtensa "
> +                          "property section %s\n"), prop_names[i]);
> +                     warned = true;
> +                   }
> +                 prop_sec->gc_mark = 1;
> +               }
> +           }
> +       }
> +    }
> +
> +  return true;
> +}
> +
> +
>  /* Create all the dynamic sections.  */
>
>  static bool
> @@ -11505,6 +11560,7 @@ static const struct bfd_elf_special_section elf_xtensa_special_sections[] =
>  #define elf_backend_finish_dynamic_sections  elf_xtensa_finish_dynamic_sections
>  #define elf_backend_finish_dynamic_symbol    elf_xtensa_finish_dynamic_symbol
>  #define elf_backend_gc_mark_hook            elf_xtensa_gc_mark_hook
> +#define elf_backend_gc_mark_extra_sections   elf_xtensa_gc_mark_extra_sections
>  #define elf_backend_grok_prstatus           elf_xtensa_grok_prstatus
>  #define elf_backend_grok_psinfo                     elf_xtensa_grok_psinfo
>  #define elf_backend_hide_symbol                     elf_xtensa_hide_symbol
> diff --git a/include/elf/xtensa.h b/include/elf/xtensa.h
> index 523855e7e81..5fb8485638f 100644
> --- a/include/elf/xtensa.h
> +++ b/include/elf/xtensa.h
> @@ -131,6 +131,9 @@ END_RELOC_NUMBERS (R_XTENSA_max)
>  #define XTENSA_LIT_SEC_NAME  ".xt.lit"
>  #define XTENSA_PROP_SEC_NAME ".xt.prop"
>
> +#define XTENSA_PROPERTY_SEC_NAMES \
> +  { XTENSA_INSN_SEC_NAME, XTENSA_LIT_SEC_NAME, XTENSA_PROP_SEC_NAME }
> +
>  typedef struct property_table_entry_t
>  {
>    bfd_vma address;
> diff --git a/ld/testsuite/ld-xtensa/gc-prop.d b/ld/testsuite/ld-xtensa/gc-prop.d
> new file mode 100644
> index 00000000000..3e8d3a07186
> --- /dev/null
> +++ b/ld/testsuite/ld-xtensa/gc-prop.d
> @@ -0,0 +1,7 @@
> +#source: gc-prop.s
> +#ld: -T gc-prop.t --gc-sections
> +#map: gc-prop.map
> +#readelf: -SW
> +#...
> + +\[ *[0-9]+\] \.xt\.prop +PROGBITS +[0-9a-f]+ +[0-9a-f]+ +0*[1-9a-f][0-9a-f]* .*
> +#pass
> diff --git a/ld/testsuite/ld-xtensa/gc-prop.map b/ld/testsuite/ld-xtensa/gc-prop.map
> new file mode 100644
> index 00000000000..85ffa79dff0
> --- /dev/null
> +++ b/ld/testsuite/ld-xtensa/gc-prop.map
> @@ -0,0 +1,9 @@
> +#...
> +Discarded input sections
> +#...
> + \.text\.dead +0x[0-9a-f]+ +0x[0-9a-f]+ .*
> +#...
> + \.xt\.prop\.dead +0x[0-9a-f]+ +0x[0-9a-f]+ .*
> +#...
> +\.xt\.prop +0x[0-9a-f]+ +0x0*[1-9a-f][0-9a-f]*
> +#pass
> diff --git a/ld/testsuite/ld-xtensa/gc-prop.s b/ld/testsuite/ld-xtensa/gc-prop.s
> new file mode 100644
> index 00000000000..56396206018
> --- /dev/null
> +++ b/ld/testsuite/ld-xtensa/gc-prop.s
> @@ -0,0 +1,9 @@
> +       .section        .text.dead,"axG",@progbits,dead,comdat
> +       .global dead
> +dead:
> +       ret
> +
> +       .text
> +       .global _start
> +_start:
> +       ret
> diff --git a/ld/testsuite/ld-xtensa/gc-prop.t b/ld/testsuite/ld-xtensa/gc-prop.t
> new file mode 100644
> index 00000000000..d493873cfce
> --- /dev/null
> +++ b/ld/testsuite/ld-xtensa/gc-prop.t
> @@ -0,0 +1,7 @@
> +ENTRY(_start)
> +SECTIONS
> +{
> +  .text 0x1000 : { *(.literal .literal.* .text .text.*) }
> +  .xt.prop 0 : { *(.xt.prop .xt.prop.* .gnu.linkonce.prop.*) }
> +  .xt.lit 0 : { *(.xt.lit .xt.lit.* .gnu.linkonce.p.*) }
> +}
> diff --git a/ld/testsuite/ld-xtensa/xtensa.exp b/ld/testsuite/ld-xtensa/xtensa.exp
> index 06349571d4f..8517f3437fd 100644
> --- a/ld/testsuite/ld-xtensa/xtensa.exp
> +++ b/ld/testsuite/ld-xtensa/xtensa.exp
> @@ -26,6 +26,7 @@ if { !([istarget "xtensa*-*-*"]) } {
>  run_dump_test "call_overflow"
>  run_dump_test "coalesce"
>  run_dump_test "diff_overflow"
> +run_dump_test "gc-prop"
>  run_dump_test "lcall"
>  run_dump_test "relax-diff1"
>  run_dump_test "relax-loc"
> --
> 2.43.0
>


-- 
Thanks.
-- Max