libelf/elf_getshstrndx.c

/* Return section index of section header string table.
   Copyright (C) 2002, 2005 Red Hat, Inc.
   Written by Ulrich Drepper <drepper@redhat.com>, 2002.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, version 2.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <assert.h>
#include <errno.h>
#include <gelf.h>
#include <stddef.h>
#include <unistd.h>

#include <system.h>
#include "libelfP.h"
#include "common.h"


int
elf_getshstrndx (elf, dst)
     Elf *elf;
     size_t *dst;
{
  int result = 0;

  if (elf == NULL)
    return -1;

  if (unlikely (elf->kind != ELF_K_ELF))
    {
      __libelf_seterrno (ELF_E_INVALID_HANDLE);
      return -1;
    }

  rwlock_rdlock (elf->lock);

  /* We rely here on the fact that the `elf' element is a common prefix
     of `elf32' and `elf64'.  */
  assert (offsetof (struct Elf, state.elf.ehdr)
	  == offsetof (struct Elf, state.elf32.ehdr));
  assert (sizeof (elf->state.elf.ehdr)
	  == sizeof (elf->state.elf32.ehdr));
  assert (offsetof (struct Elf, state.elf.ehdr)
	  == offsetof (struct Elf, state.elf64.ehdr));
  assert (sizeof (elf->state.elf.ehdr)
	  == sizeof (elf->state.elf64.ehdr));

  if (unlikely (elf->state.elf.ehdr == NULL))
    {
      __libelf_seterrno (ELF_E_WRONG_ORDER_EHDR);
      result = -1;
    }
  else
    {
      Elf32_Word num;

      num = (elf->class == ELFCLASS32
	     ? elf->state.elf32.ehdr->e_shstrndx
	     : elf->state.elf64.ehdr->e_shstrndx);

      /* Determine whether the index is too big to fit in the ELF
	 header.  */
      if (unlikely (num == SHN_XINDEX))
	{
	  /* Yes.  Search the zeroth section header.  */
	  if (elf->class == ELFCLASS32)
	    {
	      size_t offset;

	      if (elf->state.elf32.scns.data[0].shdr.e32 != NULL)
		{
		  num = elf->state.elf32.scns.data[0].shdr.e32->sh_link;
		  goto success;
		}

	      offset = elf->state.elf32.ehdr->e_shoff;

	      if (elf->map_address != NULL
		  && elf->state.elf32.ehdr->e_ident[EI_DATA] == MY_ELFDATA
		  && (ALLOW_UNALIGNED
		      || (((size_t) ((char *) elf->map_address + offset))
			  & (__alignof__ (Elf32_Shdr) - 1)) == 0))
		/* We can directly access the memory.  */
		num = ((Elf32_Shdr *) (elf->map_address + offset))->sh_link;
	      else
		{
		  /* We avoid reading in all the section headers.  Just read
		     the first one.  */
		  Elf32_Shdr shdr_mem;

		  if (unlikely (pread_retry (elf->fildes, &shdr_mem,
					     sizeof (Elf32_Shdr), offset)
				!= sizeof (Elf32_Shdr)))
		    {
		      /* We must be able to read this ELF section header.  */
		      __libelf_seterrno (ELF_E_INVALID_FILE);
		      result = -1;
		      goto out;
		    }

		  if (elf->state.elf32.ehdr->e_ident[EI_DATA] != MY_ELFDATA)
		    CONVERT (shdr_mem.sh_link);
		  num = shdr_mem.sh_link;
		}
	    }
	  else
	    {
	      if (elf->state.elf64.scns.data[0].shdr.e64 != NULL)
		{
		  num = elf->state.elf64.scns.data[0].shdr.e64->sh_link;
		  goto success;
		}

	      size_t offset = elf->state.elf64.ehdr->e_shoff;

	      if (elf->map_address != NULL
		  && elf->state.elf64.ehdr->e_ident[EI_DATA] == MY_ELFDATA
		  && (ALLOW_UNALIGNED
		      || (((size_t) ((char *) elf->map_address + offset))
			  & (__alignof__ (Elf64_Shdr) - 1)) == 0))
		/* We can directly access the memory.  */
		num = ((Elf64_Shdr *) (elf->map_address + offset))->sh_link;
	      else
		{
		  /* We avoid reading in all the section headers.  Just read
		     the first one.  */
		  Elf64_Shdr shdr_mem;

		  if (unlikely (pread_retry (elf->fildes, &shdr_mem,
					     sizeof (Elf64_Shdr), offset)
				!= sizeof (Elf64_Shdr)))
		    {
		      /* We must be able to read this ELF section header.  */
		      __libelf_seterrno (ELF_E_INVALID_FILE);
		      result = -1;
		      goto out;
		    }

		  if (elf->state.elf64.ehdr->e_ident[EI_DATA] != MY_ELFDATA)
		    CONVERT (shdr_mem.sh_link);
		  num = shdr_mem.sh_link;
		}
	    }
	}

      /* Store the result.  */
    success:
      *dst = num;
    }

 out:
  rwlock_unlock (elf->lock);

  return result;
}
INTDEF(elf_getshstrndx)