lib/libelf/elf_strptr.c

   1 /*-
   2  * Copyright (c) 2006,2008 Joseph Koshy
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 #include <assert.h>
  28 #include <gelf.h>
  29
  30 #include "_libelf.h"
  31
  32 LIBELF_VCSID("$Id$");
  33
  34 /*
  35  * Convert an ELF section#,offset pair to a string pointer.
  36  */
  37
  38 char *
  39 elf_strptr(Elf *e, size_t scndx, size_t offset)
  40 {
  41         Elf_Scn *s;
  42         Elf_Data *d;
  43         size_t alignment, count;
  44         GElf_Shdr shdr;
  45
  46         if (e == NULL || e->e_kind != ELF_K_ELF) {
  47                 LIBELF_SET_ERROR(ARGUMENT, 0);
  48                 return (NULL);
  49         }
  50
  51         if ((s = elf_getscn(e, scndx)) == NULL ||
  52             gelf_getshdr(s, &shdr) == NULL)
  53                 return (NULL);
  54
  55         if (shdr.sh_type != SHT_STRTAB ||
  56             offset >= shdr.sh_size) {
  57                 LIBELF_SET_ERROR(ARGUMENT, 0);
  58                 return (NULL);
  59         }
  60
  61         d = NULL;
  62         if (e->e_flags & ELF_F_LAYOUT) {
  63
  64                 /*
  65                  * The application is taking responsibility for the
  66                  * ELF object's layout, so we can directly translate
  67                  * an offset to a `char *' address using the `d_off'
  68                  * members of Elf_Data descriptors.
  69                  */
  70                 while ((d = elf_getdata(s, d)) != NULL) {
  71
  72                         if (d->d_buf == 0 || d->d_size == 0)
  73                                 continue;
  74
  75                         if (d->d_type != ELF_T_BYTE) {
  76                                 LIBELF_SET_ERROR(DATA, 0);
  77                                 return (NULL);
  78                         }
  79
  80                         if (offset >= d->d_off &&
  81                             offset < d->d_off + d->d_size)
  82                                 return ((char *) d->d_buf + offset - d->d_off);
  83                 }
  84         } else {
  85                 /*
  86                  * Otherwise, the `d_off' members are not useable and
  87                  * we need to compute offsets ourselves, taking into
  88                  * account 'holes' in coverage of the section introduced
  89                  * by alignment requirements.
  90                  */
  91                 count = (size_t) 0;     /* cumulative count of bytes seen */
  92                 while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
  93
  94                         if (d->d_buf == NULL || d->d_size == 0)
  95                                 continue;
  96
  97                         if (d->d_type != ELF_T_BYTE) {
  98                                 LIBELF_SET_ERROR(DATA, 0);
  99                                 return (NULL);
 100                         }
 101
 102                         if ((alignment = d->d_align) > 1) {
 103                                 if ((alignment & (alignment - 1)) != 0) {
 104                                         LIBELF_SET_ERROR(DATA, 0);
 105                                         return (NULL);
 106                                 }
 107                                 count = roundup2(count, alignment);
 108                         }
 109
 110                         if (offset < count) {
 111                                 /* offset starts in the 'hole' */
 112                                 LIBELF_SET_ERROR(ARGUMENT, 0);
 113                                 return (NULL);
 114                         }
 115
 116                         if (offset < count + d->d_size) {
 117                                 if (d->d_buf != NULL)
 118                                         return ((char *) d->d_buf +
 119                                             offset - count);
 120                                 LIBELF_SET_ERROR(DATA, 0);
 121                                 return (NULL);
 122                         }
 123
 124                         count += d->d_size;
 125                 }
 126         }
 127
 128         LIBELF_SET_ERROR(ARGUMENT, 0);
 129         return (NULL);
 130 }