ext/libelf/elf_strptr.c

   1 /*-
   2  * Copyright (c) 2006 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
  28 #include <sys/param.h>
  29 #ifdef __sun
  30 #include <sys/sysmacros.h>
  31 #endif
  32
  33 #include <assert.h>
  34 #include "gelf.h"
  35
  36 #include "_libelf.h"
  37
  38 /*
  39  * Convert an ELF section#,offset pair to a string pointer.
  40  */
  41
  42 char *
  43 elf_strptr(Elf *e, size_t scndx, size_t offset)
  44 {
  45         Elf_Scn *s;
  46         Elf_Data *d;
  47         size_t alignment, count;
  48         GElf_Shdr shdr;
  49
  50         if (e == NULL || e->e_kind != ELF_K_ELF) {
  51                 LIBELF_SET_ERROR(ARGUMENT, 0);
  52                 return (NULL);
  53         }
  54
  55         if ((s = elf_getscn(e, scndx)) == NULL ||
  56             gelf_getshdr(s, &shdr) == NULL)
  57                 return (NULL);
  58
  59         if (shdr.sh_type != SHT_STRTAB ||
  60             offset >= shdr.sh_size) {
  61                 LIBELF_SET_ERROR(ARGUMENT, 0);
  62                 return (NULL);
  63         }
  64
  65         d = NULL;
  66         if (e->e_flags & ELF_F_LAYOUT) {
  67
  68                 /*
  69                  * The application is taking responsibility for the
  70                  * ELF object's layout, so we can directly translate
  71                  * an offset to a `char *' address using the `d_off'
  72                  * members of Elf_Data descriptors.
  73                  */
  74                 while ((d = elf_getdata(s, d)) != NULL) {
  75
  76                         if (d->d_buf == 0 || d->d_size == 0)
  77                                 continue;
  78
  79                         if (d->d_type != ELF_T_BYTE) {
  80                                 LIBELF_SET_ERROR(DATA, 0);
  81                                 return (NULL);
  82                         }
  83
  84                         if (offset >= d->d_off &&
  85                             offset < d->d_off + d->d_size)
  86                                 return ((char *) d->d_buf + offset - d->d_off);
  87                 }
  88         } else {
  89                 /*
  90                  * Otherwise, the `d_off' members are not useable and
  91                  * we need to compute offsets ourselves, taking into
  92                  * account 'holes' in coverage of the section introduced
  93                  * by alignment requirements.
  94                  */
  95                 count = (size_t) 0;     /* cumulative count of bytes seen */
  96                 while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
  97
  98                         if (d->d_buf == NULL || d->d_size == 0)
  99                                 continue;
 100
 101                         if (d->d_type != ELF_T_BYTE) {
 102                                 LIBELF_SET_ERROR(DATA, 0);
 103                                 return (NULL);
 104                         }
 105
 106                         if ((alignment = d->d_align) > 1) {
 107                                 if ((alignment & (alignment - 1)) != 0) {
 108                                         LIBELF_SET_ERROR(DATA, 0);
 109                                         return (NULL);
 110                                 }
 111                                 count = roundup(count, alignment);
 112                         }
 113
 114                         if (offset < count) {
 115                                 /* offset starts in the 'hole' */
 116                                 LIBELF_SET_ERROR(ARGUMENT, 0);
 117                                 return (NULL);
 118                         }
 119
 120                         if (offset < count + d->d_size) {
 121                                 if (d->d_buf != NULL)
 122                                         return ((char *) d->d_buf +
 123                                             offset - count);
 124                                 LIBELF_SET_ERROR(DATA, 0);
 125                                 return (NULL);
 126                         }
 127
 128                         count += d->d_size;
 129                 }
 130         }
 131
 132         LIBELF_SET_ERROR(ARGUMENT, 0);
 133         return (NULL);
 134 }