elf_strptr.c revision 1.4 
1/*	$NetBSD: elf_strptr.c,v 1.4 2022/05/01 19:41:35 jkoshy Exp $	*/
2
3/*-
4 * Copyright (c) 2006,2008 Joseph Koshy
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#if HAVE_NBTOOL_CONFIG_H
30# include "nbtool_config.h"
31#endif
32
33#include <sys/param.h>
34
35#include <assert.h>
36#include <gelf.h>
37
38#include "_libelf.h"
39
40__RCSID("$NetBSD: elf_strptr.c,v 1.4 2022/05/01 19:41:35 jkoshy Exp $");
41ELFTC_VCSID("Id: elf_strptr.c 2990 2014-03-17 09:56:58Z jkoshy");
42
43/*
44 * Convert an ELF section#,offset pair to a string pointer.
45 */
46
47char *
48elf_strptr(Elf *e, size_t scndx, size_t offset)
49{
50	Elf_Scn *s;
51	Elf_Data *d;
52	GElf_Shdr shdr;
53	uint64_t alignment, count;
54
55	if (e == NULL || e->e_kind != ELF_K_ELF) {
56		LIBELF_SET_ERROR(ARGUMENT, 0);
57		return (NULL);
58	}
59
60	if ((s = elf_getscn(e, scndx)) == NULL ||
61	    gelf_getshdr(s, &shdr) == NULL)
62		return (NULL);
63
64	if (shdr.sh_type != SHT_STRTAB ||
65	    offset >= shdr.sh_size) {
66		LIBELF_SET_ERROR(ARGUMENT, 0);
67		return (NULL);
68	}
69
70	d = NULL;
71	if (e->e_flags & ELF_F_LAYOUT) {
72
73		/*
74		 * The application is taking responsibility for the
75		 * ELF object's layout, so we can directly translate
76		 * an offset to a `char *' address using the `d_off'
77		 * members of Elf_Data descriptors.
78		 */
79		while ((d = elf_getdata(s, d)) != NULL) {
80
81			if (d->d_buf == 0 || d->d_size == 0)
82				continue;
83
84			if (d->d_type != ELF_T_BYTE) {
85				LIBELF_SET_ERROR(DATA, 0);
86				return (NULL);
87			}
88
89			if (offset >= d->d_off &&
90			    offset < d->d_off + d->d_size)
91				return ((char *) d->d_buf + offset - d->d_off);
92		}
93	} else {
94		/*
95		 * Otherwise, the `d_off' members are not useable and
96		 * we need to compute offsets ourselves, taking into
97		 * account 'holes' in coverage of the section introduced
98		 * by alignment requirements.
99		 */
100		count = (uint64_t) 0;	/* cumulative count of bytes seen */
101		while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
102
103			if (d->d_buf == NULL || d->d_size == 0)
104				continue;
105
106			if (d->d_type != ELF_T_BYTE) {
107				LIBELF_SET_ERROR(DATA, 0);
108				return (NULL);
109			}
110
111			if ((alignment = d->d_align) > 1) {
112				if ((alignment & (alignment - 1)) != 0) {
113					LIBELF_SET_ERROR(DATA, 0);
114					return (NULL);
115				}
116				count = roundup2(count, alignment);
117			}
118
119			if (offset < count) {
120				/* offset starts in the 'hole' */
121				LIBELF_SET_ERROR(ARGUMENT, 0);
122				return (NULL);
123			}
124
125			if (offset < count + d->d_size) {
126				if (d->d_buf != NULL)
127					return ((char *) d->d_buf +
128					    offset - count);
129				LIBELF_SET_ERROR(DATA, 0);
130				return (NULL);
131			}
132
133			count += d->d_size;
134		}
135	}
136
137	LIBELF_SET_ERROR(ARGUMENT, 0);
138	return (NULL);
139}
140