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
43 static const char *CommentStr = ".comment";
44
45 static void
update_comment(Elf * elf,const char * file,const char * comment)46 update_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
152 int
main(int argc,char ** argv)153 main(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