glibc/elf/dl-sym-post.h

/* Post-processing of a symbol produced by dlsym, dlvsym.
   Copyright (C) 1999-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */


/* Return the link map containing the caller address.  */
static struct link_map *
_dl_sym_find_caller_link_map (ElfW(Addr) caller)
{
  struct link_map *l = _dl_find_dso_for_object (caller);
  if (l != NULL)
    return l;
  else
    /* If the address is not recognized the call comes from the main
       program (we hope).  */
    return GL(dl_ns)[LM_ID_BASE]._ns_loaded;
}

/* Translates RESULT, *REF, VALUE into a symbol address from the point
   of view of MATCH.  Performs IFUNC resolution and auditing if
   necessary.  If MATCH is NULL, CALLER is used to determine it.  */
static void *
_dl_sym_post (lookup_t result, const ElfW(Sym) *ref, void *value,
              ElfW(Addr) caller, struct link_map *match)
{
  /* Resolve indirect function address.  */
  if (__glibc_unlikely (ELFW(ST_TYPE) (ref->st_info) == STT_GNU_IFUNC))
    {
      DL_FIXUP_VALUE_TYPE fixup
        = DL_FIXUP_MAKE_VALUE (result, (ElfW(Addr)) value);
      fixup = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (fixup));
      value = (void *) DL_FIXUP_VALUE_CODE_ADDR (fixup);
    }

#ifdef SHARED
  /* Auditing checkpoint: we have a new binding.  Provide the
     auditing libraries the possibility to change the value and
     tell us whether further auditing is wanted.  */
  if (__glibc_unlikely (GLRO(dl_naudit) > 0))
    {
      const char *strtab = (const char *) D_PTR (result,
                                                 l_info[DT_STRTAB]);
      /* Compute index of the symbol entry in the symbol table of
         the DSO with the definition.  */
      unsigned int ndx = (ref - (ElfW(Sym) *) D_PTR (result,
                                                     l_info[DT_SYMTAB]));

      if (match == NULL)
        match = _dl_sym_find_caller_link_map (caller);

      if ((match->l_audit_any_plt | result->l_audit_any_plt) != 0)
        {
          unsigned int altvalue = 0;
          struct audit_ifaces *afct = GLRO(dl_audit);
          /* Synthesize a symbol record where the st_value field is
             the result.  */
          ElfW(Sym) sym = *ref;
          sym.st_value = (ElfW(Addr)) value;

          for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
            {
              struct auditstate *match_audit
                = link_map_audit_state (match, cnt);
              struct auditstate *result_audit
                = link_map_audit_state (result, cnt);
              if (afct->symbind != NULL
                  && ((match_audit->bindflags & LA_FLG_BINDFROM) != 0
                      || ((result_audit->bindflags & LA_FLG_BINDTO)
                          != 0)))
                {
                  unsigned int flags = altvalue | LA_SYMB_DLSYM;
                  uintptr_t new_value
                    = afct->symbind (&sym, ndx,
                                     &match_audit->cookie,
                                     &result_audit->cookie,
                                     &flags, strtab + ref->st_name);
                  if (new_value != (uintptr_t) sym.st_value)
                    {
                      altvalue = LA_SYMB_ALTVALUE;
                      sym.st_value = new_value;
                    }
                }

              afct = afct->next;
            }

          value = (void *) sym.st_value;
        }
    }
#endif
  return value;
}