glibc/elf/dladdr.c

/* dladdr -- Locate the shared object symbol nearest a given address.
Copyright (C) 1996 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 Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <stddef.h>
#include <link.h>
#include <dlfcn.h>


int
dladdr (void *address, Dl_info *info)
{
  const ElfW(Addr) addr = (ElfW(Addr)) address;
  struct link_map *l, *match;
  const ElfW(Sym) *symtab, *matchsym;
  const char *strtab;

  /* Find the highest-addressed object that ADDRESS is not below.  */
  match = NULL;
  for (l = _dl_loaded; l; l = l->l_next)
    if (addr >= l->l_addr && !match || match->l_addr < l->l_addr)
      match = l;

  if (match)
    {
      /* We know ADDRESS lies within MATCH if in any shared object.
	 Make sure it isn't past the end of MATCH's segments.  */
      size_t n = match->l_phnum;
      do
	--n;
      while (match->l_phdr[n].p_type != PT_LOAD);
      if (addr >= (match->l_addr +
		   match->l_phdr[n].p_vaddr + match->l_phdr[n].p_memsz))
	/* Off the end of the highest-addressed shared object.  */
	return 0;
    }
  else
    return 0;

  /* Now we know what object the address lies in.  */
  info->dli_fname = match->l_name;
  info->dli_fbase = (void *) match->l_addr;

  symtab = ((void *) match->l_addr + match->l_info[DT_SYMTAB]->d_un.d_ptr);
  strtab = ((void *) match->l_addr + match->l_info[DT_STRTAB]->d_un.d_ptr);

  /* We assume that the string table follows the symbol table, because
     there is no way in ELF to know the size of the dynamic symbol table!!  */
  for (matchsym = NULL; (void *) symtab < (void *) strtab; ++symtab)
    if (addr >= match->l_addr + symtab->st_value && !matchsym ||
	matchsym->st_value < symtab->st_value &&
	ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL ||
	ELFW(ST_BIND) (symtab->st_info) == STB_WEAK)
      matchsym = symtab;

  if (matchsym)
    {
      /* We found a symbol close by.  Fill in its name and exact address.  */
      info->dli_sname = strtab + matchsym->st_name;
      info->dli_saddr = (void *) (match->l_addr + matchsym->st_value);
    }
  else
    {
      /* No symbol matches.  We return only the containing object.  */
      info->dli_sname = NULL;
      info->dli_saddr = NULL;
    }

  return 1;
}