objdiff.c

   1 /*  Copyright (C) 2008  Jeffrey Brian Arnold <jbarnold@mit.edu>
   2  *
   3  *  This program is free software; you can redistribute it and/or modify
   4  *  it under the terms of the GNU General Public License, version 2.
   5  *
   6  *  This program is distributed in the hope that it will be useful,
   7  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   8  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   9  *  GNU General Public License for more details.
  10  *
  11  *  You should have received a copy of the GNU General Public License
  12  *  along with this program; if not, write to the Free Software
  13  *  Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA
  14  *  02110-1301, USA.
  15  */
  16
  17 /*
  18  * "objdiff old.o new.o" prints two lists to STDOUT, one per line:
  19  * (1) the names of the ELF sections in new.o that either
  20  *     (a) do not appear in old.o, or
  21  *     (b) have different contents in old.o and new.o
  22  * (2) the names of the "entry point" ELF symbols in new.o
  23  *     corresponding to the ELF sections in list (1)
  24  *
  25  * Before printing these two lists, objdiff prints the number of bits
  26  * per address on the target architecture.
  27  */
  28
  29 #include "objcommon.h"
  30 #include "objdiff.h"
  31
  32 bfd *newbfd;
  33 asymbol **new_sympp, **old_sympp;
  34 int new_symcount, old_symcount;
  35
  36 int main(int argc, char **argv)
  37 {
  38         bfd_init();
  39         bfd *oldbfd = bfd_openr(argv[1], NULL);
  40         assert(oldbfd != NULL);
  41         newbfd = bfd_openr(argv[2], NULL);
  42         assert(newbfd != NULL);
  43
  44         char **matching;
  45         assert(bfd_check_format_matches(oldbfd, bfd_object, &matching));
  46         assert(bfd_check_format_matches(newbfd, bfd_object, &matching));
  47
  48         new_symcount = get_syms(newbfd, &new_sympp);
  49         old_symcount = get_syms(oldbfd, &old_sympp);
  50
  51         printf("%d\n", bfd_arch_bits_per_address(oldbfd));
  52         foreach_nonmatching(oldbfd, newbfd, print_newbfd_section_name);
  53         printf("\n");
  54         foreach_nonmatching(oldbfd, newbfd, print_newbfd_entry_symbols);
  55         printf("\n");
  56
  57         assert(bfd_close(oldbfd));
  58         assert(bfd_close(newbfd));
  59         return EXIT_SUCCESS;
  60 }
  61
  62 void foreach_nonmatching(bfd *oldbfd, bfd *newbfd, section_fn s_fn)
  63 {
  64         asection *newp, *oldp;
  65         for (newp = newbfd->sections; newp != NULL; newp = newp->next) {
  66                 if (!starts_with(newp->name, ".text"))
  67                         continue;
  68                 oldp = bfd_get_section_by_name(oldbfd, newp->name);
  69                 if (oldp == NULL) {
  70                         if (s_fn == print_newbfd_section_name)
  71                                 s_fn(newp);
  72                         continue;
  73                 }
  74                 int newsize = bfd_get_section_size(newp);
  75                 int oldsize = bfd_get_section_size(oldp);
  76                 if (newsize == oldsize) {
  77                         void *newmem = malloc(newsize);
  78                         void *oldmem = malloc(oldsize);
  79                         assert(bfd_get_section_contents
  80                                (oldbfd, oldp, oldmem, 0, oldsize));
  81                         assert(bfd_get_section_contents
  82                                (newbfd, newp, newmem, 0, newsize));
  83                         if (memcmp(newmem, oldmem, newsize) == 0 &&
  84                             reloc_cmp(oldbfd, oldp, newbfd, newp) == 0)
  85                                 continue;
  86                 }
  87                 s_fn(newp);
  88         }
  89 }
  90
  91 /*
  92  * reloc_cmp checks to see whether the old section and the new section
  93  * reference different read-only data in their relocations -- if a hard-coded
  94  * string has been changed between the old file and the new file, reloc_cmp
  95  * will detect the difference.
  96  */
  97 int reloc_cmp(bfd *oldbfd, asection *oldp, bfd *newbfd, asection *newp)
  98 {
  99         int i;
 100         struct supersect *old_ss, *new_ss;
 101
 102         old_ss = fetch_supersect(oldbfd, oldp, old_sympp);
 103         new_ss = fetch_supersect(newbfd, newp, new_sympp);
 104
 105         if (old_ss->num_relocs != new_ss->num_relocs)
 106                 return -1;
 107
 108         for (i = 0; i < old_ss->num_relocs; i++) {
 109                 struct supersect *ro_old_ss, *ro_new_ss;
 110
 111                 asection *ro_oldp = (*old_ss->relocs[i]->sym_ptr_ptr)->section;
 112                 asection *ro_newp = (*new_ss->relocs[i]->sym_ptr_ptr)->section;
 113
 114                 ro_old_ss = fetch_supersect(oldbfd, ro_oldp, old_sympp);
 115                 ro_new_ss = fetch_supersect(newbfd, ro_newp, new_sympp);
 116
 117                 if (!starts_with(ro_old_ss->name, ".rodata"))
 118                         continue;
 119
 120                 if (strcmp(ro_old_ss->name, ro_new_ss->name) != 0)
 121                         return -1;
 122
 123                 int old_offset =
 124                     *(int *)(old_ss->contents + old_ss->relocs[i]->address);
 125                 int new_offset =
 126                     *(int *)(new_ss->contents + new_ss->relocs[i]->address);
 127
 128                 if (starts_with(ro_old_ss->name, ".rodata.str")) {
 129                         if (strcmp
 130                             (ro_old_ss->contents + old_offset,
 131                              ro_new_ss->contents + new_offset) != 0)
 132                                 return -1;
 133                         continue;
 134                 }
 135
 136                 if (ro_old_ss->contents_size != ro_new_ss->contents_size)
 137                         return -1;
 138
 139                 if (memcmp(ro_old_ss->contents,
 140                            ro_new_ss->contents, ro_old_ss->contents_size) != 0)
 141                         return -1;
 142         }
 143
 144         return 0;
 145 }
 146
 147 void print_newbfd_section_name(asection *sect)
 148 {
 149         printf("%s ", sect->name);
 150 }
 151
 152 void print_newbfd_entry_symbols(asection *sect)
 153 {
 154         int i;
 155         for (i = 0; i < new_symcount; i++) {
 156                 if (strlen(new_sympp[i]->name) != 0 &&
 157                     !starts_with(new_sympp[i]->name, ".text") &&
 158                     strcmp(new_sympp[i]->section->name, sect->name) == 0) {
 159                         printf("%s ", new_sympp[i]->name);
 160                 }
 161         }
 162 }