elf_strptr.c revision 1.1 
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
34ELFTC_VCSID("Id: elf_strptr.c 2271 2011-12-03 17:06:35Z jkoshy ");
35
36/*
37 * Convert an ELF section#,offset pair to a string pointer.
38 */
39
40char *
41elf_strptr(Elf *e, size_t scndx, size_t offset)
42{
43	Elf_Scn *s;
44	Elf_Data *d;
45	size_t alignment, count;
46	GElf_Shdr shdr;
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 = (size_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