xref: /third_party/elfutils/libelf/elf_getshdrstrndx.c

/* Return section index of section header string table.
   Copyright (C) 2002, 2005, 2009, 2014, 2015 Red Hat, Inc.
   This file is part of elfutils.
   Written by Ulrich Drepper <drepper@redhat.com>, 2002.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at
       your option) any later version

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

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

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

#include "libelfP.h"
#include "common.h"


int
elf_getshdrstrndx (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 (unlikely (elf->state.elf32.scns.cnt == 0))
		{
		  /* Cannot use SHN_XINDEX without section headers.  */
		  __libelf_seterrno (ELF_E_INVALID_SECTION_HEADER);
		  result = -1;
		  goto out;
		}

	      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
			   + elf->start_offset + offset))
			  & (__alignof__ (Elf32_Shdr) - 1)) == 0))
		{
		  /* First see whether the information in the ELF header is
		     valid and it does not ask for too much.  */
		  if (unlikely (elf->maximum_size - offset
				< sizeof (Elf32_Shdr)))
		    {
		      /* Something is wrong.  */
		      __libelf_seterrno (ELF_E_INVALID_SECTION_HEADER);
		      result = -1;
		      goto out;
		    }

		  /* We can directly access the memory.  */
		  num = ((Elf32_Shdr *) (elf->map_address + elf->start_offset
					 + offset))->sh_link;
		}
	      else
		{
		  /* We avoid reading in all the section headers.  Just read
		     the first one.  */
		  Elf32_Shdr shdr_mem;
		  ssize_t r;

		  if (unlikely ((r = pread_retry (elf->fildes, &shdr_mem,
						  sizeof (Elf32_Shdr), offset))
				!= sizeof (Elf32_Shdr)))
		    {
		      /* We must be able to read this ELF section header.  */
		      if (r < 0)
			__libelf_seterrno (ELF_E_INVALID_FILE);
		      else
			__libelf_seterrno (ELF_E_INVALID_ELF);
		      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 (unlikely (elf->state.elf64.scns.cnt == 0))
		{
		  /* Cannot use SHN_XINDEX without section headers.  */
		  __libelf_seterrno (ELF_E_INVALID_SECTION_HEADER);
		  result = -1;
		  goto out;
		}

	      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
			   + elf->start_offset + offset))
			  & (__alignof__ (Elf64_Shdr) - 1)) == 0))
		{
		  /* First see whether the information in the ELF header is
		     valid and it does not ask for too much.  */
		  if (unlikely (elf->maximum_size - offset
				< sizeof (Elf64_Shdr)))
		    {
		      /* Something is wrong.  */
		      __libelf_seterrno (ELF_E_INVALID_SECTION_HEADER);
		      result = -1;
		      goto out;
		    }

		  /* We can directly access the memory.  */
		  num = ((Elf64_Shdr *) (elf->map_address + elf->start_offset
					 + offset))->sh_link;
		}
	      else
		{
		  /* We avoid reading in all the section headers.  Just read
		     the first one.  */
		  Elf64_Shdr shdr_mem;
		  ssize_t r;

		  if (unlikely ((r = pread_retry (elf->fildes, &shdr_mem,
						  sizeof (Elf64_Shdr), offset))
				!= sizeof (Elf64_Shdr)))
		    {
		      /* We must be able to read this ELF section header.  */
		      if (r < 0)
			__libelf_seterrno (ELF_E_INVALID_FILE);
		      else
			__libelf_seterrno (ELF_E_INVALID_ELF);
		      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_getshdrstrndx)
/* Alias for the deprecated name.  */
strong_alias (elf_getshdrstrndx, elf_getshstrndx)