xref: /third_party/elfutils/libdwelf/dwelf_elf_gnu_build_id.c

/* Returns the build id if found in a NT_GNU_BUILD_ID note.
   Copyright (C) 2014 Red Hat, Inc.
   This file is part of elfutils.

   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 "libdwelfP.h"
#include "libdwflP.h"

#define NO_VADDR	((GElf_Addr) -1l)

static int
check_notes (Elf_Data *data, GElf_Addr data_elfaddr,
             const void **build_id_bits, GElf_Addr *build_id_elfaddr,
             int *build_id_len)
{
  size_t pos = 0;
  GElf_Nhdr nhdr;
  size_t name_pos;
  size_t desc_pos;
  while ((pos = gelf_getnote (data, pos, &nhdr, &name_pos, &desc_pos)) > 0)
    if (nhdr.n_type == NT_GNU_BUILD_ID
	&& nhdr.n_namesz == sizeof "GNU"
	&& !memcmp (data->d_buf + name_pos, "GNU", sizeof "GNU"))
	{
	  *build_id_bits = data->d_buf + desc_pos;
	  *build_id_elfaddr = (data_elfaddr == NO_VADDR
	                      ? 0 : data_elfaddr + desc_pos);
	  *build_id_len = nhdr.n_descsz;
	  return 1;
	}
  return 0;
}

/* Defined here for reuse. The dwelf interface doesn't care about the
   address of the note, but libdwfl does.  */
static int
find_elf_build_id (Dwfl_Module *mod, int e_type, Elf *elf,
		   const void **build_id_bits, GElf_Addr *build_id_elfaddr,
		   int *build_id_len)
{
  size_t shstrndx = SHN_UNDEF;
  int result = 0;

  Elf_Scn *scn = elf_nextscn (elf, NULL);

  if (scn == NULL)
    {
      /* No sections, have to look for phdrs.  */
      size_t phnum;
      if (unlikely (elf_getphdrnum (elf, &phnum) != 0))
	{
	  if (mod != NULL)
	    __libdwfl_seterrno (DWFL_E_LIBELF);
	  return -1;
	}
      for (size_t i = 0; result == 0 && i < phnum; ++i)
	{
	  GElf_Phdr phdr_mem;
	  GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
	  if (likely (phdr != NULL) && phdr->p_type == PT_NOTE)
	    result = check_notes (elf_getdata_rawchunk (elf,
							phdr->p_offset,
							phdr->p_filesz,
							(phdr->p_align == 8
							 ? ELF_T_NHDR8
							 : ELF_T_NHDR)),
				  phdr->p_vaddr,
				  build_id_bits,
				  build_id_elfaddr,
				  build_id_len);
	}
    }
  else
    do
      {
	GElf_Shdr shdr_mem;
	GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
	if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
	  {
	    /* Determine the right sh_addr in this module.  */
	    GElf_Addr vaddr = 0;
	    if (!(shdr->sh_flags & SHF_ALLOC))
	      vaddr = NO_VADDR;
	    else if (mod == NULL || e_type != ET_REL)
	      vaddr = shdr->sh_addr;
	    else if (__libdwfl_relocate_value (mod, elf, &shstrndx,
					       elf_ndxscn (scn), &vaddr))
	      vaddr = NO_VADDR;
	    result = check_notes (elf_getdata (scn, NULL), vaddr,
	                          build_id_bits,
	                          build_id_elfaddr,
	                          build_id_len);
	  }
      }
    while (result == 0 && (scn = elf_nextscn (elf, scn)) != NULL);

  return result;
}

int
internal_function
__libdwfl_find_elf_build_id (Dwfl_Module *mod, Elf *elf,
			     const void **build_id_bits,
			     GElf_Addr *build_id_elfaddr, int *build_id_len)
{
  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
  if (unlikely (ehdr == NULL))
    {
      __libdwfl_seterrno (DWFL_E_LIBELF);
      return -1;
    }
  // MOD->E_TYPE is zero here.
  assert (ehdr->e_type != ET_REL || mod != NULL);

  return find_elf_build_id (mod, ehdr->e_type, elf,
			    build_id_bits, build_id_elfaddr, build_id_len);
}

ssize_t
dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp)
{
  GElf_Addr build_id_elfaddr;
  int build_id_len;
  int result = find_elf_build_id (NULL, ET_NONE, elf, build_idp,
				  &build_id_elfaddr, &build_id_len);
  if (result > 0)
    return build_id_len;

  return result;
}
INTDEF(dwelf_elf_gnu_build_id)