Re: [PATCH 3/4] Add run-time chesk for single global definition

[Florian Weimer <fweimer@redhat.com>]

* H. J. Lu via Libc-alpha:

> +static inline void __attribute__ ((always_inline))
> +_dl_check_protected_symbol (const char *undef_name,
> +			    const struct link_map *undef_map,
> +			    const ElfW(Sym) *ref,
> +			    const struct link_map *map,
> +			    int type_class)
> +{
> +  if (undef_map != NULL
> +      && !(undef_map->l_1_needed
> +	   & GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION)
> +      && (map->l_1_needed
> +	  & GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION))
> +    {
> +      if ((type_class & ELF_RTYPE_CLASS_COPY))
> +	/* Disallow copy relocations against protected data symbols in
> +	   an object with single global definition.  */
> +	_dl_fatal_printf ("copy relocation against non-copyable protected symbol=%s in file=%s\n",
> +			  undef_name, DSO_FILENAME (map->l_name));
> +      else if (ref->st_value != 0
> +	       && ref->st_shndx == SHN_UNDEF
> +	       && (type_class & ELF_RTYPE_CLASS_PLT))
> +	/* Disallow non-zero symbol values of undefined symbols, which
> +	   are used as the function pointer, against protected function
> +	   symbols in an object with single global definition.  */
> +	_dl_fatal_printf ("non-canonical reference to canonical protected function symbol=%s in file=%s\n",
> +			  undef_name, DSO_FILENAME (map->l_name));
> +    }
> +}

Why are those fatal errors?

I have trouble understanding the second comment (for the
ELF_RTYPE_CLASS_PLT).

Thanks,
Florian