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 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD$");
29
30 #include <sys/param.h>
31
32 #include <assert.h>
33 #include <gelf.h>
34
35 #include "_libelf.h"
36
37 /*
38 * Convert an ELF section#,offset pair to a string pointer.
39 */
40
41 char *
elf_strptr(Elf * e,size_t scndx,size_t offset)42 elf_strptr(Elf *e, size_t scndx, size_t offset)
43 {
44 Elf_Scn *s;
45 Elf_Data *d;
46 size_t alignment, count;
47 GElf_Shdr shdr;
48
49 if (e == NULL || e->e_kind != ELF_K_ELF) {
50 LIBELF_SET_ERROR(ARGUMENT, 0);
51 return (NULL);
52 }
53
54 if ((s = elf_getscn(e, scndx)) == NULL ||
55 gelf_getshdr(s, &shdr) == NULL)
56 return (NULL);
57
58 if (/*shdr.sh_type != SHT_STRTAB || */
59 offset >= shdr.sh_size) {
60 LIBELF_SET_ERROR(ARGUMENT, 0);
61 return (NULL);
62 }
63
64 d = NULL;
65 if (e->e_flags & ELF_F_LAYOUT) {
66
67 /*
68 * The application is taking responsibility for the
69 * ELF object's layout, so we can directly translate
70 * an offset to a `char *' address using the `d_off'
71 * members of Elf_Data descriptors.
72 */
73 while ((d = elf_getdata(s, d)) != NULL) {
74
75 if (d->d_buf == 0 || d->d_size == 0)
76 continue;
77
78 if (d->d_type != ELF_T_BYTE) {
79 LIBELF_SET_ERROR(DATA, 0);
80 return (NULL);
81 }
82
83 if (offset >= d->d_off &&
84 offset < d->d_off + d->d_size)
85 return ((char *) d->d_buf + offset - d->d_off);
86 }
87 } else {
88 /*
89 * Otherwise, the `d_off' members are not useable and
90 * we need to compute offsets ourselves, taking into
91 * account 'holes' in coverage of the section introduced
92 * by alignment requirements.
93 */
94 count = (size_t) 0; /* cumulative count of bytes seen */
95 while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
96
97 if (d->d_buf == NULL || d->d_size == 0)
98 continue;
99
100 if (d->d_type != ELF_T_BYTE) {
101 LIBELF_SET_ERROR(DATA, 0);
102 return (NULL);
103 }
104
105 if ((alignment = d->d_align) > 1) {
106 if ((alignment & (alignment - 1)) != 0) {
107 LIBELF_SET_ERROR(DATA, 0);
108 return (NULL);
109 }
110 count = roundup2(count, alignment);
111 }
112
113 if (offset < count) {
114 /* offset starts in the 'hole' */
115 LIBELF_SET_ERROR(ARGUMENT, 0);
116 return (NULL);
117 }
118
119 if (offset < count + d->d_size) {
120 if (d->d_buf != NULL)
121 return ((char *) d->d_buf +
122 offset - count);
123 LIBELF_SET_ERROR(DATA, 0);
124 return (NULL);
125 }
126
127 count += d->d_size;
128 }
129 }
130
131 LIBELF_SET_ERROR(ARGUMENT, 0);
132 return (NULL);
133 }
134