src/elfcmp.c

/* Compare relevant content of two ELF files.
   Copyright (C) 2005 Red Hat, Inc.
   Written by Ulrich Drepper <drepper@redhat.com>, 2005.

   This program is Open Source software; you can redistribute it and/or
   modify it under the terms of the Open Software License version 1.0 as
   published by the Open Source Initiative.

   You should have received a copy of the Open Software License along
   with this program; if not, you may obtain a copy of the Open Software
   License version 1.0 from http://www.opensource.org/licenses/osl.php or
   by writing the Open Source Initiative c/o Lawrence Rosen, Esq.,
   3001 King Ranch Road, Ukiah, CA 95482.   */

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

#include <argp.h>
#include <assert.h>
#include <errno.h>
#include <error.h>
#include <fcntl.h>
#include <libintl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "../libelf/elf-knowledge.h"
#include "../libebl/libeblP.h"


/* Prototypes of local functions.  */
static Elf *open_file (const char *fname, int *fdp, Ebl **eblp);
static bool search_for_copy_reloc (Ebl *ebl, size_t scnndx, int symndx);
static  int regioncompare (const void *p1, const void *p2);


/* Name and version of program.  */
static void print_version (FILE *stream, struct argp_state *state);
void (*argp_program_version_hook) (FILE *, struct argp_state *) = print_version;

/* Bug report address.  */
const char *argp_program_bug_address = PACKAGE_BUGREPORT;

/* Values for the parameters which have no short form.  */
#define OPT_GAPS 0x100

/* Definitions of arguments for argp functions.  */
static const struct argp_option options[] =
{
  { NULL, 0, NULL, 0, N_("Control options:"), 0 },
  { "gaps", OPT_GAPS, "ACTION", 0, N_("Control treatment of gaps in loadable segments [ignore|match] (default: ignore)"), 0 },
  { "quiet", 'q', NULL, 0, N_("Output nothing; yield exit status only"), 0 },

  { NULL, 0, NULL, 0, N_("Miscellaneous:"), 0 },
  { NULL, 0, NULL, 0, NULL, 0 }
};

/* Short description of program.  */
static const char doc[] = N_("\
Compare relevant parts of two ELF files for equality.");

/* Strings for arguments in help texts.  */
static const char args_doc[] = N_("FILE1 FILE2");

/* Prototype for option handler.  */
static error_t parse_opt (int key, char *arg, struct argp_state *state);

/* Data structure to communicate with argp functions.  */
static struct argp argp =
{
  options, parse_opt, args_doc, doc, NULL, NULL, NULL
};


/* How to treat gaps in loadable segments.  */
static enum
  {
    gaps_ignore = 0,
    gaps_match
  }
  gaps;

/* Structure to hold information about used regions.  */
struct region
{
  GElf_Addr from;
  GElf_Addr to;
  struct region *next;
};

/* Nonzero if only exit status is wanted.  */
static bool quiet;


int
main (int argc, char *argv[])
{
  /* Set locale.  */
  (void) setlocale (LC_ALL, "");

  /* Make sure the message catalog can be found.  */
  (void) bindtextdomain (PACKAGE, LOCALEDIR);

  /* Initialize the message catalog.  */
  (void) textdomain (PACKAGE);

  /* Parse and process arguments.  */
  int remaining;
  (void) argp_parse (&argp, argc, argv, 0, &remaining, NULL);

  /* We expect exactly two non-option parameters.  */
  if (remaining + 2 != argc)
    {
      fputs (gettext ("Invalid number of parameters.\n"), stderr);
      argp_help (&argp, stderr, ARGP_HELP_SEE, program_invocation_short_name);
      exit (1);
    }

  /* Comparing the files is done in two phases:
     1. compare all sections.  Sections which are irrelevant (i.e., if
        strip would remove them) are ignored.  Some section types are
	handled special.
     2. all parts of the loadable segments which are not parts of any
        section is compared according to the rules of the --gaps option.
  */
  int result = 0;
  elf_version (EV_CURRENT);

  const char *const fname1 = argv[remaining];
  int fd1;
  Ebl *ebl1;
  Elf *elf1 = open_file (fname1, &fd1, &ebl1);

  const char *const fname2 = argv[remaining + 1];
  int fd2;
  Ebl *ebl2;
  Elf *elf2 = open_file (fname2, &fd2, &ebl2);

  GElf_Ehdr ehdr1_mem;
  GElf_Ehdr *ehdr1 = gelf_getehdr (elf1, &ehdr1_mem);
  if (ehdr1 == NULL)
    error (EXIT_FAILURE, 0, gettext ("cannot get ELF header of \"%s\": %s"),
	   fname1, elf_errmsg (-1));
  GElf_Ehdr ehdr2_mem;
  GElf_Ehdr *ehdr2 = gelf_getehdr (elf2, &ehdr2_mem);
  if (ehdr2 == NULL)
    error (EXIT_FAILURE, 0, gettext ("cannot get ELF header of \"%s\": %s"),
	   fname2, elf_errmsg (-1));

  /* Compare the ELF headers.  */
  if (memcmp (ehdr1->e_ident, ehdr2->e_ident, EI_NIDENT) != 0
      || ehdr1->e_type != ehdr2->e_type
      || ehdr1->e_machine != ehdr2->e_machine
      || ehdr1->e_version != ehdr2->e_version
      || ehdr1->e_entry != ehdr2->e_entry
      || ehdr1->e_phoff != ehdr2->e_phoff
      || ehdr1->e_flags != ehdr2->e_flags
      || ehdr1->e_ehsize != ehdr2->e_ehsize
      || ehdr1->e_phentsize != ehdr2->e_phentsize
      || ehdr1->e_phnum != ehdr2->e_phnum
      || ehdr1->e_shentsize != ehdr2->e_shentsize
      || ehdr1->e_shnum != ehdr2->e_shnum
      || ehdr1->e_shstrndx != ehdr2->e_shstrndx)
    {
      if (! quiet)
	error (0, 0, gettext ("%s %s diff: ELF header"), fname1, fname2);
      result = 1;
      goto out;
    }

  /* Iterate over all sections.  We expect the sections in the two
     files to match exactly.  */
  Elf_Scn *scn1 = NULL;
  Elf_Scn *scn2 = NULL;
  struct region *regions = NULL;
  size_t nregions = 0;
  while (1)
    {
      GElf_Shdr shdr1_mem;
      GElf_Shdr *shdr1;
      const char *sname1 = NULL;
      do
	{
	  scn1 = elf_nextscn (elf1, scn1);
	  shdr1 = gelf_getshdr (scn1, &shdr1_mem);
	  if (shdr1 != NULL)
	    sname1 = elf_strptr (elf1, ehdr1->e_shstrndx, shdr1->sh_name);
	}
      while (scn1 != NULL
	     && ebl_section_strip_p (ebl1, ehdr1, shdr1, sname1, true, false));

      GElf_Shdr shdr2_mem;
      GElf_Shdr *shdr2;
      const char *sname2 = NULL;
      do
	{
	  scn2 = elf_nextscn (elf2, scn2);
	  shdr2 = gelf_getshdr (scn2, &shdr2_mem);
	  if (shdr2 != NULL)
	    sname2 = elf_strptr (elf2, ehdr2->e_shstrndx, shdr2->sh_name);
	}
      while (scn2 != NULL
	     && ebl_section_strip_p (ebl2, ehdr2, shdr2, sname2, true, false));

      if (scn1 == NULL || scn2 == NULL)
	break;

      if (gaps != gaps_ignore && (shdr1->sh_flags & SHF_ALLOC) != 0)
	{
	  struct region *newp = (struct region *) alloca (sizeof (*newp));
	  newp->from = shdr1->sh_offset;
	  newp->to = shdr1->sh_offset + shdr1->sh_size;
	  newp->next = regions;
	  regions = newp;

	  ++nregions;
	}

      /* Compare the headers.  We allow the name to be at a different
	 location.  */
      if (strcmp (sname1, sname2) != 0)
	{
	header_mismatch:
	  error (0, 0, gettext ("%s %s differ: section header"),
		 fname1, fname2);
	  result = 1;
	  goto out;
	}

      /* We ignore certain sections.  */
      if (strcmp (sname1, ".gnu_debuglink") == 0
	  || strcmp (sname1, ".gnu.prelink_undo") == 0)
	continue;

      if (shdr1->sh_type != shdr2->sh_type
	  // XXX Any flags which should be ignored?
	  || shdr1->sh_flags != shdr2->sh_flags
	  || shdr1->sh_addr != shdr2->sh_addr
	  || shdr1->sh_offset != shdr2->sh_offset
	  || shdr1->sh_size != shdr2->sh_size
	  || shdr1->sh_link != shdr2->sh_link
	  || shdr1->sh_info != shdr2->sh_info
	  || shdr1->sh_addralign != shdr2->sh_addralign
	  || shdr1->sh_entsize != shdr2->sh_entsize)
	goto header_mismatch;

      Elf_Data *data1 = elf_getdata (scn1, NULL);
      if (data1 == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get content of section %zu in \"%s\": %s"),
	       elf_ndxscn (scn1), fname1, elf_errmsg (-1));

      Elf_Data *data2 = elf_getdata (scn2, NULL);
      if (data2 == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get content of section %zu in \"%s\": %s"),
	       elf_ndxscn (scn2), fname2, elf_errmsg (-1));

      switch (shdr1->sh_type)
	{
	case SHT_DYNSYM:
	case SHT_SYMTAB:
	  /* Iterate over the symbol table.  We ignore the st_size
	     value of undefined symbols.  */
	  for (int ndx = 0; ndx < (int) (shdr1->sh_size / shdr1->sh_entsize);
	       ++ndx)
	    {
	      GElf_Sym sym1_mem;
	      GElf_Sym *sym1 = gelf_getsym (data1, ndx, &sym1_mem);
	      if (sym1 == NULL)
		error (EXIT_FAILURE, 0,
		       gettext ("cannot get symbol in \"%s\": %s"),
		       fname1, elf_errmsg (-1));
	      GElf_Sym sym2_mem;
	      GElf_Sym *sym2 = gelf_getsym (data2, ndx, &sym2_mem);
	      if (sym2 == NULL)
		error (EXIT_FAILURE, 0,
		       gettext ("cannot get symbol in \"%s\": %s"),
		       fname2, elf_errmsg (-1));

	      const char *name1 = elf_strptr (elf1, shdr1->sh_link,
					      sym1->st_name);
	      const char *name2 = elf_strptr (elf2, shdr2->sh_link,
					      sym2->st_name);
	      if (strcmp (name1, name2) != 0
		  || sym1->st_value != sym2->st_value
		  || (sym1->st_size != sym2->st_size
		      && sym1->st_shndx != SHN_UNDEF)
		  || sym1->st_info != sym2->st_info
		  || sym1->st_other != sym2->st_other
		  || sym1->st_shndx != sym1->st_shndx)
		{
		  // XXX Do we want to allow reordered symbol tables?
		  if (! quiet)
		    error (0, 0, gettext ("%s %s differ: symbol table"),
			   fname1, fname2);
		  result = 1;
		  goto out;
		}

	      if (sym1->st_shndx == SHN_UNDEF
		  && sym1->st_size != sym2->st_size)
		{
		  /* The size of the symbol in the object defining it
		     might have changed.  That is OK unless the symbol
		     is used in a copy relocation.  Look over the
		     sections in both files and determine which
		     relocation section uses this symbol table
		     section.  Then look through the relocations to
		     see whether any copy relocation references this
		     symbol.  */
		  if (search_for_copy_reloc (ebl1, elf_ndxscn (scn1), ndx)
		      || search_for_copy_reloc (ebl2, elf_ndxscn (scn2), ndx))
		    {
		      if (! quiet)
			error (0, 0, gettext ("%s %s differ: symbol table"),
			       fname1, fname2);
		      result = 1;
		      goto out;
		    }
		}
	    }
	  break;

	default:
	  /* Compare the section content byte for byte.  */
	  assert (shdr1->sh_type == SHT_NOBITS
		  || (data1->d_buf != NULL || data1->d_size == 0));
	  assert (shdr2->sh_type == SHT_NOBITS
		  || (data2->d_buf != NULL || data1->d_size == 0));

	  if (data1->d_size != data2->d_size
	      || (shdr1->sh_type != SHT_NOBITS
		  && memcmp (data1->d_buf, data2->d_buf, data1->d_size) != 0))
	    {
	      if (! quiet)
		error (0, 0, gettext ("%s %s differ: section content"),
		       fname1, fname2);
	      result = 1;
	      goto out;
	    }
	  break;
	}
    }

  if (scn1 != scn2)
    {
      if (! quiet)
	error (0, 0,
	       gettext ("%s %s differ: unequal amount of important sections"),
	       fname1, fname2);
      result = 1;
      goto out;
    }

  /* We we look at gaps, create artificial ones for the parts of the
     program which we are not in sections.  */
  struct region ehdr_region;
  struct region phdr_region;
  if (gaps != gaps_ignore)
    {
      ehdr_region.from = 0;
      ehdr_region.to = ehdr1->e_ehsize;
      ehdr_region.next = &phdr_region;

      phdr_region.from = ehdr1->e_phoff;
      phdr_region.to = ehdr1->e_phoff + ehdr1->e_phnum * ehdr1->e_phentsize;
      phdr_region.next = regions;

      regions = &ehdr_region;
      nregions += 2;
    }

  /* If we need to look at the gaps we need access to the file data.  */
  char *raw1 = NULL;
  size_t size1 = 0;
  char *raw2 = NULL;
  size_t size2 = 0;
  struct region *regionsarr = alloca (nregions * sizeof (struct region));
  if (gaps != gaps_ignore)
    {
      raw1 = elf_rawfile (elf1, &size1);
      if (raw1 == NULL )
	error (EXIT_FAILURE, 0, gettext ("cannot load data of \"%s\": %s"),
	       fname1, elf_errmsg (-1));

      raw2 = elf_rawfile (elf2, &size2);
      if (raw2 == NULL )
	error (EXIT_FAILURE, 0, gettext ("cannot load data of \"%s\": %s"),
	       fname2, elf_errmsg (-1));

      for (size_t cnt = 0; cnt < nregions; ++cnt)
	{
	  regionsarr[cnt] = *regions;
	  regions = regions->next;
	}

      qsort (regionsarr, nregions, sizeof (regionsarr[0]), regioncompare);
    }

  /* Compare the program header tables.  */
  for (int ndx = 0; ndx < ehdr1->e_phnum; ++ndx)
    {
      GElf_Phdr phdr1_mem;
      GElf_Phdr *phdr1 = gelf_getphdr (elf1, ndx, &phdr1_mem);
      if (ehdr1 == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get program header entry %d of \"%s\": %s"),
	       ndx, fname1, elf_errmsg (-1));
      GElf_Phdr phdr2_mem;
      GElf_Phdr *phdr2 = gelf_getphdr (elf2, ndx, &phdr2_mem);
      if (ehdr2 == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get program header entry %d of \"%s\": %s"),
	       ndx, fname2, elf_errmsg (-1));

      if (memcmp (phdr1, phdr2, sizeof (GElf_Phdr)) != 0)
	{
	  if (! quiet)
	    error (0, 0, gettext ("%s %s differ: program header %d"),
		   fname1, fname2, ndx);
	  result = 1;
	  goto out;
	}

      if (gaps != gaps_ignore && phdr1->p_type == PT_LOAD)
	{
	  size_t cnt = 0;
	  while (cnt < nregions && regionsarr[cnt].to < phdr1->p_offset)
	    ++cnt;

	  GElf_Off last = phdr1->p_offset;
	  GElf_Off end = phdr1->p_offset + phdr1->p_filesz;
	  while (cnt < nregions && regionsarr[cnt].from < end)
	    {
	      if (last < regionsarr[cnt].from)
		{
		  /* Compare the [LAST,FROM) region.  */
		  assert (gaps == gaps_match);
		  if (memcmp (raw1 + last, raw2 + last,
			      regionsarr[cnt].from - last) != 0)
		    {
		    gapmismatch:
		      if (!quiet)
			error (0, 0, gettext ("%s %s differ: gap"),
			       fname1, fname2);
		      result = 1;
		      goto out;
		    }

		}
	      last = regionsarr[cnt].to;
	      ++cnt;
	    }

	  if (cnt == nregions && last < end)
	    goto gapmismatch;
	}
    }

 out:
  elf_end (elf1);
  elf_end (elf2);
  close (fd1);
  close (fd2);

  return result;
}


/* Print the version information.  */
static void
print_version (FILE *stream, struct argp_state *state __attribute__ ((unused)))
{
  fprintf (stream, "elfcmp (%s) %s\n", PACKAGE_NAME, VERSION);
  fprintf (stream, gettext ("\
Copyright (C) %s Red Hat, Inc.\n\
This is free software; see the source for copying conditions.  There is NO\n\
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\
"), "2005");
  fprintf (stream, gettext ("Written by %s.\n"), "Ulrich Drepper");
}


/* Handle program arguments.  */
static error_t
parse_opt (int key, char *arg,
	   struct argp_state *state __attribute__ ((unused)))
{
  switch (key)
    {
    case 'q':
      quiet = true;
      break;

    case OPT_GAPS:
      if (strcasecmp (arg, "ignore") == 0)
	gaps = gaps_ignore;
      else if (strcasecmp (arg, "match") == 0)
	gaps = gaps_match;
      else
	{
	  fprintf (stderr,
		   gettext ("Invalid value \"%s\" for --gaps parameter."),
		   arg);
	  argp_help (&argp, stderr, ARGP_HELP_SEE,
		     program_invocation_short_name);
	  exit (1);
	}
      break;

    default:
      return ARGP_ERR_UNKNOWN;
    }
  return 0;
}


static Elf *
open_file (const char *fname, int *fdp, Ebl **eblp)
{
  int fd = open (fname, O_RDONLY);
  if (unlikely (fd == -1))
    error (EXIT_FAILURE, errno, gettext ("cannot open \"%s\""), fname);
  Elf *elf = elf_begin (fd, ELF_C_READ_MMAP, NULL);
  if (elf == NULL)
    error (EXIT_FAILURE, 0,
	   gettext ("cannot create ELF descriptor for \"%s\": %s"),
	   fname, elf_errmsg (-1));
  Ebl *ebl = ebl_openbackend (elf);
  if (ebl == NULL)
    error (EXIT_FAILURE, 0,
	   gettext ("cannot create EBL descriptor for \"%s\""), fname);

  *fdp = fd;
  *eblp = ebl;
  return elf;
}


static bool
search_for_copy_reloc (Ebl *ebl, size_t scnndx, int symndx)
{
  Elf_Scn *scn = NULL;
  while ((scn = elf_nextscn (ebl->elf, scn)) != NULL)
    {
      GElf_Shdr shdr_mem;
      GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
      if (shdr == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get section header of section %zu: %s"),
	       elf_ndxscn (scn), elf_errmsg (-1));

      if ((shdr->sh_type != SHT_REL && shdr->sh_type != SHT_RELA)
	  || shdr->sh_link != scnndx)
	continue;

      Elf_Data *data = elf_getdata (scn, NULL);
      if (data == NULL)
	error (EXIT_FAILURE, 0,
	       gettext ("cannot get content of section %zu: %s"),
	       elf_ndxscn (scn), elf_errmsg (-1));

      if (shdr->sh_type == SHT_REL)
	for (int ndx = 0; ndx < (int) (shdr->sh_size / shdr->sh_entsize);
	     ++ndx)
	  {
	    GElf_Rel rel_mem;
	    GElf_Rel *rel = gelf_getrel (data, ndx, &rel_mem);
	    if (rel == NULL)
	      error (EXIT_FAILURE, 0, gettext ("cannot get relocation: %s"),
		     elf_errmsg (-1));

	    if ((int) GELF_R_SYM (rel->r_info) == symndx
		&& ebl_copy_reloc_p (ebl, GELF_R_TYPE (rel->r_info)))
	      return true;
	  }
      else
	for (int ndx = 0; ndx < (int) (shdr->sh_size / shdr->sh_entsize);
	     ++ndx)
	  {
	    GElf_Rela rela_mem;
	    GElf_Rela *rela = gelf_getrela (data, ndx, &rela_mem);
	    if (rela == NULL)
	      error (EXIT_FAILURE, 0, gettext ("cannot get relocation: %s"),
		     elf_errmsg (-1));

	    if ((int) GELF_R_SYM (rela->r_info) == symndx
		&& ebl_copy_reloc_p (ebl, GELF_R_TYPE (rela->r_info)))
	      return true;
	  }
    }

  return false;
}


static  int
regioncompare (const void *p1, const void *p2)
{
  const struct region *r1 = (const struct region *) p1;
  const struct region *r2 = (const struct region *) p2;

  if (r1->from < r2->from)
    return -1;
  return 1;
}