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