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 <sys/param.h> 28 29 #include <assert.h> 30 #include <gelf.h> 31 32 #include "_libelf.h" 33 34 ELFTC_VCSID("$Id: elf_strptr.c 2990 2014-03-17 09:56:58Z jkoshy $"); 35 36 /* 37 * Convert an ELF section#,offset pair to a string pointer. 38 */ 39 40 char * 41 elf_strptr(Elf *e, size_t scndx, size_t offset) 42 { 43 Elf_Scn *s; 44 Elf_Data *d; 45 GElf_Shdr shdr; 46 uint64_t alignment, count; 47 48 if (e == NULL || e->e_kind != ELF_K_ELF) { 49 LIBELF_SET_ERROR(ARGUMENT, 0); 50 return (NULL); 51 } 52 53 if ((s = elf_getscn(e, scndx)) == NULL || 54 gelf_getshdr(s, &shdr) == NULL) 55 return (NULL); 56 57 if (shdr.sh_type != SHT_STRTAB || 58 offset >= shdr.sh_size) { 59 LIBELF_SET_ERROR(ARGUMENT, 0); 60 return (NULL); 61 } 62 63 d = NULL; 64 if (e->e_flags & ELF_F_LAYOUT) { 65 66 /* 67 * The application is taking responsibility for the 68 * ELF object's layout, so we can directly translate 69 * an offset to a `char *' address using the `d_off' 70 * members of Elf_Data descriptors. 71 */ 72 while ((d = elf_getdata(s, d)) != NULL) { 73 74 if (d->d_buf == 0 || d->d_size == 0) 75 continue; 76 77 if (d->d_type != ELF_T_BYTE) { 78 LIBELF_SET_ERROR(DATA, 0); 79 return (NULL); 80 } 81 82 if (offset >= d->d_off && 83 offset < d->d_off + d->d_size) 84 return ((char *) d->d_buf + offset - d->d_off); 85 } 86 } else { 87 /* 88 * Otherwise, the `d_off' members are not useable and 89 * we need to compute offsets ourselves, taking into 90 * account 'holes' in coverage of the section introduced 91 * by alignment requirements. 92 */ 93 count = (uint64_t) 0; /* cumulative count of bytes seen */ 94 while ((d = elf_getdata(s, d)) != NULL && count <= offset) { 95 96 if (d->d_buf == NULL || d->d_size == 0) 97 continue; 98 99 if (d->d_type != ELF_T_BYTE) { 100 LIBELF_SET_ERROR(DATA, 0); 101 return (NULL); 102 } 103 104 if ((alignment = d->d_align) > 1) { 105 if ((alignment & (alignment - 1)) != 0) { 106 LIBELF_SET_ERROR(DATA, 0); 107 return (NULL); 108 } 109 count = roundup2(count, alignment); 110 } 111 112 if (offset < count) { 113 /* offset starts in the 'hole' */ 114 LIBELF_SET_ERROR(ARGUMENT, 0); 115 return (NULL); 116 } 117 118 if (offset < count + d->d_size) { 119 if (d->d_buf != NULL) 120 return ((char *) d->d_buf + 121 offset - count); 122 LIBELF_SET_ERROR(DATA, 0); 123 return (NULL); 124 } 125 126 count += d->d_size; 127 } 128 } 129 130 LIBELF_SET_ERROR(ARGUMENT, 0); 131 return (NULL); 132 } 133