[PATCH] LTO: Handle __real_SYM reference in IR

[H.J. Lu]

On Fri, Apr 29, 2022 at 10:59 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> When an IR symbol SYM is referenced in IR via __real_SYM, its resolution
> should be LDPR_PREVAILING_DEF, not PREVAILING_DEF_IRONLY, since LTO
> doesn't know that __real_SYM should be resolved by SYM.
>
> bfd/
>
>         PR ld/29086
>         * elflink.c (_bfd_elf_merge_symbol): Mark SYM is referenced in
>         IR if __real_SYM is referenced in IR.
>
> include/
>
>         PR ld/29086
>         * bfdlink.h (bfd_link_hash_entry): Add ir_ref_real.
>
> ld/
>
>         PR ld/29086
>         * plugin.c (get_symbols): Resolve SYM definition to
>         LDPR_PREVAILING_DEF for __real_SYM reference in IR.
>         * testsuite/ld-plugin/lto.exp: Run PR ld/29086 test.
>         * testsuite/ld-plugin/pr29086.c: New file.
> ---
>  bfd/elflink.c                    | 15 +++++++++++++--
>  include/bfdlink.h                |  4 ++++
>  ld/plugin.c                      |  7 +++++--
>  ld/testsuite/ld-plugin/lto.exp   |  8 ++++++++
>  ld/testsuite/ld-plugin/pr29086.c | 19 +++++++++++++++++++
>  5 files changed, 49 insertions(+), 4 deletions(-)
>  create mode 100644 ld/testsuite/ld-plugin/pr29086.c
>
> diff --git a/bfd/elflink.c b/bfd/elflink.c
> index b54ee517c75..ced07e40524 100644
> --- a/bfd/elflink.c
> +++ b/bfd/elflink.c
> @@ -1101,8 +1101,19 @@ _bfd_elf_merge_symbol (bfd *abfd,
>    if (! bfd_is_und_section (sec))
>      h = elf_link_hash_lookup (elf_hash_table (info), name, true, false, false);
>    else
> -    h = ((struct elf_link_hash_entry *)
> -        bfd_wrapped_link_hash_lookup (abfd, info, name, true, false, false));
> +    {
> +      h = ((struct elf_link_hash_entry *)
> +          bfd_wrapped_link_hash_lookup (abfd, info, name, true, false,
> +                                        false));
> +      /* Mark SYM is referenced in IR if __real_SYM is referenced in
> +        IR.  */
> +      if (h != NULL
> +         && info->wrap_hash != NULL
> +         && (abfd->flags & BFD_PLUGIN) != 0
> +         && strcmp (h->root.root.string,
> +                    name + sizeof "__real_" - 1) == 0)
> +       h->root.ir_ref_real = 1;
> +    }
>    if (h == NULL)
>      return false;
>    *sym_hash = h;
> diff --git a/include/bfdlink.h b/include/bfdlink.h
> index b16f3f44ca5..3b8cc7f8f96 100644
> --- a/include/bfdlink.h
> +++ b/include/bfdlink.h
> @@ -114,6 +114,10 @@ struct bfd_link_hash_entry
>       as distinct from a LTO IR object file.  */
>    unsigned int non_ir_ref_dynamic : 1;
>
> +  /* The symbol, SYM, is referenced by __real_SYM in an LTO IR object
> +     file.  */
> +  unsigned int ir_ref_real : 1;
> +
>    /* Symbol is a built-in define.  These will be overridden by PROVIDE
>       in a linker script.  */
>    unsigned int linker_def : 1;
> diff --git a/ld/plugin.c b/ld/plugin.c
> index 6db52d16802..c8cdf580a67 100644
> --- a/ld/plugin.c
> +++ b/ld/plugin.c
> @@ -863,8 +863,11 @@ get_symbols (const void *handle, int nsyms, struct ld_plugin_symbol *syms,
>           /* We need to know if the sym is referenced from non-IR files.  Or
>              even potentially-referenced, perhaps in a future final link if
>              this is a partial one, perhaps dynamically at load-time if the
> -            symbol is externally visible.  Also check for wrapper symbol.  */
> -         if (blhe->non_ir_ref_regular || wrap_status == wrapper)
> +            symbol is externally visible.  Also check for __real_SYM
> +            reference and wrapper symbol.  */
> +         if (blhe->non_ir_ref_regular
> +             || blhe->ir_ref_real
> +             || wrap_status == wrapper)
>             res = LDPR_PREVAILING_DEF;
>           else if (wrap_status == wrapped)
>             res = LDPR_RESOLVED_IR;
> diff --git a/ld/testsuite/ld-plugin/lto.exp b/ld/testsuite/ld-plugin/lto.exp
> index 33af6c45a41..fa5d2500aa3 100644
> --- a/ld/testsuite/ld-plugin/lto.exp
> +++ b/ld/testsuite/ld-plugin/lto.exp
> @@ -522,6 +522,14 @@ set lto_link_elf_tests [list \
>     {{"nm" {-D} "pr28849.d"}} \
>     "pr28849" \
>    ] \
> +  [list \
> +   "PR ld/pr29086" \
> +   "-Wl,--wrap=foo" \
> +   "-O0 -flto" \
> +   {pr29086.c} \
> +   {} \
> +   "pr29086" \
> +  ] \
>  ]
>
>  # PR 14918 checks that libgcc is not spuriously included in a shared link of
> diff --git a/ld/testsuite/ld-plugin/pr29086.c b/ld/testsuite/ld-plugin/pr29086.c
> new file mode 100644
> index 00000000000..d333d68e262
> --- /dev/null
> +++ b/ld/testsuite/ld-plugin/pr29086.c
> @@ -0,0 +1,19 @@
> +int
> +foo (void)
> +{
> +  return 0;
> +}
> +
> +int
> +main ()
> +{
> +  return foo ();
> +}
> +
> +extern int __real_foo (void);
> +
> +int
> +__wrap_foo (void)
> +{
> +  return __real_foo ();
> +}
> --
> 2.35.1
>

Hi Nick, Alan,

Can you review this?

Thanks.

-- 
H.J.