[PATCH v3] elf: Always honor the first definition in shared object and archive

[Alan Modra]

On Fri, Mar 15, 2024 at 12:43:50PM -0700, H.J. Lu wrote:
> GCC doesn't put builtin function symbol references, which are defined in
> the shared C library, in the IR symbol table.

Should we be covering for what looks like a gcc bug?  At the expense
of yet another hash table.

> +  /* Hash table of symbols which are first defined in archives or shared
> +     objects when there are any IR inputs.  */
> +  struct bfd_link_hash_table *first_hash;
> +

It looks to me that you just need a hash table that maps a symbol name
to a bfd.  Maybe use libiberty/hashtab.c hash instead, to cut down
memory for entries?

> +		  if (e->type == bfd_link_hash_new)
> +		    {
> +		      /* Change the type to bfd_link_hash_defined and
> +			 store ABFD in u.undef->abfd.  */
> +		      e->type = bfd_link_hash_defined;
> +		      e->u.undef.abfd = abfd;
> +		    }

That's a bit rude, using bfd_link_hash_defined and a union field that
belongs to bfd_link_hash_undefined.

> @@ -5963,7 +6017,30 @@ _bfd_elf_archive_symbol_lookup (bfd *abfd,
>  
>    p = strchr (name, ELF_VER_CHR);
>    if (p == NULL || p[1] != ELF_VER_CHR)
> -    return h;
> +    {
> +      struct elf_link_hash_table *htab = elf_hash_table (info);
> +      if (htab->first_hash != NULL)
> +	{
> +	  /* Add this symbol to first hash if this archive has the
> +	     first definition.  */
> +	  struct bfd_link_hash_entry *e
> +	    = bfd_link_hash_lookup (htab->first_hash, name, true,
> +				    false, true);
> +	  if (e == NULL)
> +	    info->callbacks->einfo
> +	      (_("%F%P: %pB: failed to add %s to first hash\n"),
> +	       abfd, name);
> +
> +	  if (e->type == bfd_link_hash_new)
> +	    {
> +	      /* Change the type to bfd_link_hash_defined and store
> +		 ABFD in u.undef->abfd.  */
> +	      e->type = bfd_link_hash_defined;
> +	      e->u.undef.abfd = abfd;
> +	    }
> +	}
> +      return h;
> +    }

At first glance this looks like a duplicate of the code in
elf_link_add_object_symbols adding an entry to first_hash, and
therefore could be extracted to a common function.

-- 
Alan Modra
Australia Development Lab, IBM