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
42char *
43elf_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}
135