elf_strptr.c revision 4484:7c56a6c9c265 
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
30#include <assert.h>
31#include "gelf.h"
32
33#include "_libelf.h"
34
35/*
36 * Convert an ELF section#,offset pair to a string pointer.
37 */
38
39char *
40elf_strptr(Elf *e, size_t scndx, size_t offset)
41{
42        Elf_Scn *s;
43        Elf_Data *d;
44        size_t alignment, count;
45        GElf_Shdr shdr;
46
47        if (e == NULL || e->e_kind != ELF_K_ELF) {
48                LIBELF_SET_ERROR(ARGUMENT, 0);
49                return (NULL);
50        }
51
52        if ((s = elf_getscn(e, scndx)) == NULL ||
53            gelf_getshdr(s, &shdr) == NULL)
54                return (NULL);
55
56        if (shdr.sh_type != SHT_STRTAB ||
57            offset >= shdr.sh_size) {
58                LIBELF_SET_ERROR(ARGUMENT, 0);
59                return (NULL);
60        }
61
62        d = NULL;
63        if (e->e_flags & ELF_F_LAYOUT) {
64
65                /*
66                 * The application is taking responsibility for the
67                 * ELF object's layout, so we can directly translate
68                 * an offset to a `char *' address using the `d_off'
69                 * members of Elf_Data descriptors.
70                 */
71                while ((d = elf_getdata(s, d)) != NULL) {
72
73                        if (d->d_buf == 0 || d->d_size == 0)
74                                continue;
75
76                        if (d->d_type != ELF_T_BYTE) {
77                                LIBELF_SET_ERROR(DATA, 0);
78                                return (NULL);
79                        }
80
81                        if (offset >= d->d_off &&
82                            offset < d->d_off + d->d_size)
83                                return ((char *) d->d_buf + offset - d->d_off);
84                }
85        } else {
86                /*
87                 * Otherwise, the `d_off' members are not useable and
88                 * we need to compute offsets ourselves, taking into
89                 * account 'holes' in coverage of the section introduced
90                 * by alignment requirements.
91                 */
92                count = (size_t) 0;	/* cumulative count of bytes seen */
93                while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
94
95                        if (d->d_buf == NULL || d->d_size == 0)
96                                continue;
97
98                        if (d->d_type != ELF_T_BYTE) {
99                                LIBELF_SET_ERROR(DATA, 0);
100                                return (NULL);
101                        }
102
103                        if ((alignment = d->d_align) > 1) {
104                                if ((alignment & (alignment - 1)) != 0) {
105                                        LIBELF_SET_ERROR(DATA, 0);
106                                        return (NULL);
107                                }
108                                count = roundup(count, alignment);
109                        }
110
111                        if (offset < count) {
112                                /* offset starts in the 'hole' */
113                                LIBELF_SET_ERROR(ARGUMENT, 0);
114                                return (NULL);
115                        }
116
117                        if (offset < count + d->d_size) {
118                                if (d->d_buf != NULL)
119                                        return ((char *) d->d_buf +
120                                            offset - count);
121                                LIBELF_SET_ERROR(DATA, 0);
122                                return (NULL);
123                        }
124
125                        count += d->d_size;
126                }
127        }
128
129        LIBELF_SET_ERROR(ARGUMENT, 0);
130        return (NULL);
131}
132