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
41char *
42elf_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