1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21/*
22 * Copyright (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved.
23 */
24
25/*
26 * acom: Append Comment
27 *
28 * This program demonstrates the use of the libelf interface to
29 * modify a ELF file. This program will open an ELF file and
30 * either modify an existing .comment section and/or append
31 * a new .comment section to an existing ELF file.
32 */
33
34#include <stdio.h>
35#include <libelf.h>
36#include <gelf.h>
37#include <fcntl.h>
38#include <unistd.h>
39#include <stdlib.h>
40#include <string.h>
41
42
43static const char	*CommentStr =	".comment";
44
45static void
46update_comment(Elf *elf, const char *file, const char *comment)
47{
48	Elf_Scn		*scn = NULL;
49	GElf_Shdr	shdr;
50	Elf_Data	*data;
51	size_t		shstrndx;
52
53	if (elf_getshdrstrndx(elf, &shstrndx) == -1) {
54		(void) fprintf(stderr, "%s: gelf_getshdrstrdx() failed: %s\n",
55		    file, elf_errmsg(0));
56		return;
57	}
58
59	while ((scn = elf_nextscn(elf, scn)) != NULL) {
60		/*
61		 * Do a string compare to examine each section header
62		 * to see if it is a ".comment" section.  If it is then
63		 * this is the section we want to process.
64		 */
65		if (gelf_getshdr(scn, &shdr) == NULL) {
66			(void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
67			    file, elf_errmsg(0));
68			return;
69		}
70		if (strcmp(CommentStr, elf_strptr(elf, shstrndx,
71		    shdr.sh_name)) == 0)
72			break;
73	}
74
75	if (scn == NULL) {
76		int	ndx;
77
78		(void) printf("%s has no .comment section.  "
79		    "Creating one...\n", file);
80		/*
81		 * First add the ".comment" string to the string table
82		 */
83		if ((scn = elf_getscn(elf, shstrndx)) == NULL) {
84			(void) fprintf(stderr, "%s: elf_getscn() failed: %s\n",
85			    file, elf_errmsg(0));
86			return;
87		}
88		if ((data = elf_getdata(scn, NULL)) == NULL) {
89			(void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
90			    file, elf_errmsg(0));
91			return;
92		}
93		ndx = data->d_off + data->d_size;
94		if ((data = elf_newdata(scn)) == NULL) {
95			(void) fprintf(stderr, "%s: elf_newdata() failed: %s\n",
96			    file, elf_errmsg(0));
97			return;
98		}
99		data->d_buf = (void *)CommentStr;
100		data->d_size = strlen(CommentStr) + 1;
101		data->d_align = 1;
102
103		/*
104		 * Add the ".comment" section to the end of the file.
105		 * Initialize the fields in the Section Header that
106		 * libelf will not fill in.
107		 */
108		if ((scn = elf_newscn(elf)) == NULL) {
109			(void) fprintf(stderr, "%s: elf_newscn() failed: %s\n",
110			    file, elf_errmsg(0));
111			return;
112		}
113		if (gelf_getshdr(scn, &shdr) == NULL) {
114			(void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
115			    file, elf_errmsg(0));
116			return;
117		}
118		shdr.sh_name = ndx;
119		shdr.sh_type = SHT_PROGBITS;
120		shdr.sh_flags = 0;
121		shdr.sh_addr = 0;
122		shdr.sh_link = 0;
123		shdr.sh_info = 0;
124
125		/*
126		 * Flush the changes to the underlying elf32 or elf64
127		 * section header.
128		 */
129		(void) gelf_update_shdr(scn, &shdr);
130	}
131
132	if (shdr.sh_addr != 0) {
133		(void) printf("%s: .comment section is part of a "
134		    "loadable segment, it cannot be changed.\n", file);
135		return;
136	}
137
138	if ((data = elf_newdata(scn)) == NULL) {
139		(void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
140		    file, elf_errmsg(0));
141		return;
142	}
143	data->d_buf = (void *)comment;
144	data->d_size = strlen(comment) + 1;
145	data->d_align = 1;
146
147	if (elf_update(elf, ELF_C_WRITE) == -1)
148		(void) fprintf(stderr, "%s: elf_update() failed: %s\n", file,
149		    elf_errmsg(0));
150}
151
152int
153main(int argc, char **argv)
154{
155	int	i;
156	char	*new_comment;
157
158
159	if (argc < 3) {
160		(void) printf("usage: %s <new comment> elf_file ...\n",
161		    argv[0]);
162		return (1);
163	}
164
165	/*
166	 * Initialize the elf library, must be called before elf_begin()
167	 * can be called.
168	 */
169	if (elf_version(EV_CURRENT) == EV_NONE) {
170		(void) fprintf(stderr, "elf_version() failed: %s\n",
171		    elf_errmsg(0));
172		return (1);
173	}
174
175	/*
176	 * The new comment is passed in through the command line.
177	 * This string will be used to update the .comment section of
178	 * the specified ELF files.
179	 */
180	new_comment = argv[1];
181	for (i = 2; i < argc; i++) {
182		int	fd;
183		Elf	*elf;
184		char	*elf_fname;
185
186		elf_fname = argv[i];
187		if ((fd = open(elf_fname, O_RDWR)) == -1) {
188			perror("open");
189			continue;
190		}
191
192		/*
193		 * Attempt to open an Elf descriptor Read/Write
194		 * for each file.
195		 */
196		if ((elf = elf_begin(fd, ELF_C_RDWR, 0)) == NULL) {
197			(void) fprintf(stderr, "elf_begin() failed: %s\n",
198			    elf_errmsg(0));
199			(void) close(fd);
200			continue;
201		}
202		/*
203		 * Determine what kind of elf file this is:
204		 */
205		if (elf_kind(elf) == ELF_K_ELF)
206			update_comment(elf, elf_fname, new_comment);
207		else
208			(void) printf("%s not of type ELF_K_ELF.  "
209			    "elf_kind == %d\n", elf_fname, elf_kind(elf));
210
211		(void) elf_end(elf);
212		(void) close(fd);
213	}
214
215	return (0);
216}
217