1 /*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
26
27 /*
28 * Name: fix_empty_sec_hdr_flags.c
29 *
30 * Description: Remove the SHF_ALLOC flag from "empty" section headers.
31 * An "empty" section header has sh_addr == 0 and sh_size == 0.
32 *
33 * This program is adapted from the example program shown on the
34 * elf(3elf) man page and from code from the Solaris compiler
35 * driver.
36 */
37
38 #include <fcntl.h>
39 #include <stdio.h>
40 #include <libelf.h>
41 #include <stdlib.h>
42 #include <string.h>
43 #include <unistd.h>
44
45 static void failure(void);
46
47 void
main(int argc,char ** argv)48 main(int argc, char ** argv) {
49 void * ehdr; /* ELF header */
50 unsigned int i; /* section counter */
51 int fd; /* descriptor for file */
52 Elf * elf; /* ELF descriptor */
53 char * elf_ident; /* ELF identity string */
54 char * elf_obj; /* elf_obj file */
55 int fix_count; /* number of flags fixed */
56 int is_elfclass64; /* is an ELFCLASS64 file? */
57 Elf_Scn * scn; /* ELF section descriptor */
58 void * shdr; /* ELF section header */
59 Elf_Data * shstrtab; /* ELF section header string table */
60
61 if (argc != 2) {
62 (void) fprintf(stderr, "Usage: %s elf_obj\n", argv[0]);
63 exit(2);
64 }
65
66 /* open the elf_obj */
67 elf_obj = argv[1];
68 if ((fd = open(elf_obj, O_RDWR)) == -1) {
69 (void) fprintf(stderr, "%s: cannot open file.\n", elf_obj);
70 exit(3);
71 }
72
73 (void) printf("Opening '%s' for update\n", elf_obj);
74 (void) fflush(stdout);
75 (void) elf_version(EV_CURRENT); /* coordinate ELF versions */
76
77 /* obtain the ELF descriptors from the input file */
78 if ((elf = elf_begin(fd, ELF_C_RDWR, NULL)) == NULL) {
79 failure();
80 }
81
82 /* determine if ELFCLASS64 or not? */
83 elf_ident = elf_getident(elf, NULL);
84 is_elfclass64 = (elf_ident[EI_CLASS] == ELFCLASS64);
85
86 /* get the ELF header */
87 if (is_elfclass64) {
88 ehdr = elf64_getehdr(elf);
89 } else {
90 ehdr = elf32_getehdr(elf);
91 }
92 if (ehdr == NULL) {
93 failure();
94 }
95
96 /* get the ELF section descriptor */
97 if (is_elfclass64) {
98 scn = elf_getscn(elf, ((Elf64_Ehdr *) ehdr)->e_shstrndx);
99 } else {
100 scn = elf_getscn(elf, ((Elf32_Ehdr *) ehdr)->e_shstrndx);
101 }
102 if (scn == NULL) {
103 failure();
104 }
105
106 /* get the section header string table */
107 shstrtab = elf_getdata(scn, NULL);
108 if (shstrtab == NULL) {
109 failure();
110 }
111
112 fix_count = 0;
113
114 /* traverse the sections of the input file */
115 for (i = 1, scn = NULL; scn = elf_nextscn(elf, scn); i++) {
116 int has_flag_set; /* is SHF_ALLOC flag set? */
117 int is_empty; /* is section empty? */
118 char * name; /* short hand pointer */
119
120 /* get the section header */
121 if (is_elfclass64) {
122 shdr = elf64_getshdr(scn);
123 } else {
124 shdr = elf32_getshdr(scn);
125 }
126 if (shdr == NULL) {
127 failure();
128 }
129
130 if (is_elfclass64) {
131 name = (char *)shstrtab->d_buf + ((Elf64_Shdr *) shdr)->sh_name;
132 } else {
133 name = (char *)shstrtab->d_buf + ((Elf32_Shdr *) shdr)->sh_name;
134 }
135
136 if (is_elfclass64) {
137 has_flag_set = ((Elf64_Shdr *) shdr)->sh_flags & SHF_ALLOC;
138 is_empty = ((Elf64_Shdr *) shdr)->sh_addr == 0 &&
139 ((Elf64_Shdr *) shdr)->sh_size == 0;
140 } else {
141 has_flag_set = ((Elf32_Shdr *) shdr)->sh_flags & SHF_ALLOC;
142 is_empty = ((Elf32_Shdr *) shdr)->sh_addr == 0 &&
143 ((Elf32_Shdr *) shdr)->sh_size == 0;
144 }
145
146 if (is_empty && has_flag_set) {
147 (void) printf("section[%u] '%s' is empty, "
148 "but SHF_ALLOC flag is set.\n", i, name);
149 (void) printf("Clearing the SHF_ALLOC flag.\n");
150
151 if (is_elfclass64) {
152 ((Elf64_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC;
153 } else {
154 ((Elf32_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC;
155 }
156 fix_count++;
157 }
158 } /* end for each ELF section */
159
160 if (fix_count > 0) {
161 (void) printf("Saving %d updates to '%s'\n", fix_count, elf_obj);
162 (void) fflush(stdout);
163 (void) elf_update(elf, ELF_C_NULL); /* recalc ELF memory structures */
164 (void) elf_update(elf, ELF_C_WRITE); /* write out changes to ELF obj */
165 } else {
166 (void) printf("No SHF_ALLOC flags needed to be cleared.\n");
167 }
168
169 (void) elf_end(elf); /* done with ELF obj */
170 (void) close(fd);
171
172 (void) printf("Done %s '%s'\n",
173 (fix_count > 0) ? "updating" : "with", elf_obj);
174 (void) fflush(stdout);
175 exit(0);
176 } /* end main */
177
178
179 static void
failure()180 failure() {
181 (void) fprintf(stderr, "%s\n", elf_errmsg(elf_errno()));
182 exit(6);
183 }
184