1 /* Test program for copying a whole ELF file using libelf.
2 Copyright (C) 2018 Red Hat, Inc.
3 This file is part of elfutils.
4
5 This file is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 elfutils is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17
18
19 #ifdef HAVE_CONFIG_H
20 # include <config.h>
21 #endif
22
23 #include <errno.h>
24 #include <fcntl.h>
25 #include <inttypes.h>
26 #include <stdbool.h>
27 #include <stdio.h>
28 #include <stdlib.h>
29 #include <string.h>
30 #include <unistd.h>
31 #include <sys/types.h>
32 #include <sys/stat.h>
33
34 #include ELFUTILS_HEADER(elf)
35 #include <gelf.h>
36
37
38 /* shstrndx is special, might overflow into section zero header sh_link. */
39 static int
setshstrndx(Elf * elf,size_t ndx)40 setshstrndx (Elf *elf, size_t ndx)
41 {
42 printf ("setshstrndx: %zd\n", ndx);
43
44 GElf_Ehdr ehdr_mem;
45 GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
46 if (ehdr == NULL)
47 return -1;
48
49 if (ndx < SHN_LORESERVE)
50 ehdr->e_shstrndx = ndx;
51 else
52 {
53 ehdr->e_shstrndx = SHN_XINDEX;
54 Elf_Scn *zscn = elf_getscn (elf, 0);
55 GElf_Shdr zshdr_mem;
56 GElf_Shdr *zshdr = gelf_getshdr (zscn, &zshdr_mem);
57 if (zshdr == NULL)
58 return -1;
59 zshdr->sh_link = ndx;
60 if (gelf_update_shdr (zscn, zshdr) == 0)
61 return -1;
62 }
63
64 if (gelf_update_ehdr (elf, ehdr) == 0)
65 return -1;
66
67 return 0;
68 }
69
70 /* Copies all elements of an ELF file either using mmap or read. */
71 static void
copy_elf(const char * in,const char * out,bool use_mmap)72 copy_elf (const char *in, const char *out, bool use_mmap)
73 {
74 printf ("\ncopy_elf: %s -> %s (%s)\n", in, out, use_mmap ? "mmap" : "read");
75
76 /* Existing ELF file. */
77 int fda = open (in, O_RDONLY);
78 if (fda < 0)
79 {
80 fprintf (stderr, "Couldn't open file '%s': %s\n",
81 in, strerror (errno));
82 exit (1);
83 }
84
85 Elf *elfa = elf_begin (fda, use_mmap ? ELF_C_READ_MMAP : ELF_C_READ, NULL);
86 if (elfa == NULL)
87 {
88 fprintf (stderr, "Couldn't open ELF file '%s': %s\n",
89 in, elf_errmsg (-1));
90 exit (1);
91 }
92
93 /* Open new file. */
94 int fdb = open (out, O_RDWR | O_CREAT | O_TRUNC, 0644);
95 if (fdb < 0)
96 {
97 fprintf (stderr, "Couldn't create file '%s': %s\n",
98 out, strerror (errno));
99 exit (1);
100 }
101
102 Elf *elfb = elf_begin (fdb, use_mmap ? ELF_C_WRITE_MMAP : ELF_C_WRITE, NULL);
103 if (elfb == NULL)
104 {
105 fprintf (stderr, "Couldn't create ELF file '%s': %s\n",
106 out, elf_errmsg (-1));
107 exit (1);
108 }
109
110 // Copy ELF header.
111 GElf_Ehdr ehdr_mema;
112 GElf_Ehdr *ehdra = gelf_getehdr (elfa, &ehdr_mema);
113 if (ehdra == NULL)
114 {
115 printf ("cannot get ELF header: %s\n", elf_errmsg (-1));
116 exit (1);
117 }
118
119 int class = gelf_getclass (elfa);
120 // Create an ELF header.
121 if (gelf_newehdr (elfb, class) == 0)
122 {
123 printf ("cannot create ELF header: %s\n", elf_errmsg (-1));
124 exit (1);
125 }
126
127 /* New elf header is an exact copy. */
128 GElf_Ehdr ehdr_memb;
129 GElf_Ehdr *ehdrb = &ehdr_memb;
130 *ehdrb = *ehdra;
131 if (gelf_update_ehdr (elfb, ehdrb) == 0)
132 {
133 printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
134 exit (1);
135 }
136
137 /* shstrndx is special. (Technically phdrnum and shdrnum are also
138 special, but they are handled by libelf.) */
139 size_t shstrndx;
140 if (elf_getshdrstrndx (elfa, &shstrndx) < 0)
141 {
142 printf ("cannot get shstrndx: %s\n", elf_errmsg (-1));
143 exit (1);
144 }
145 if (setshstrndx (elfb, shstrndx) < 0)
146 {
147 printf ("cannot set shstrndx: %s\n", elf_errmsg (-1));
148 exit (1);
149 }
150
151 /* If there are phdrs, copy them over. */
152 size_t phnum;
153 if (elf_getphdrnum (elfa, &phnum) != 0)
154 {
155 printf ("cannot get phdrs: %s\n", elf_errmsg (-1));
156 exit (1);
157 }
158
159 if (phnum > 0)
160 {
161 if (gelf_newphdr (elfb, phnum) == 0)
162 {
163 printf ("cannot create phdrs: %s\n", elf_errmsg (-1));
164 exit (1);
165 }
166
167 for (size_t cnt = 0; cnt < phnum; ++cnt)
168 {
169 GElf_Phdr phdr_mem;
170 GElf_Phdr *phdr = gelf_getphdr (elfa, cnt, &phdr_mem);
171 if (phdr == NULL)
172 {
173 printf ("couldn't get phdr %zd: %s\n", cnt, elf_errmsg (-1));
174 exit (1);
175 }
176
177 if (gelf_update_phdr (elfb, cnt, phdr) == 0)
178 {
179 printf ("couldn't update phdr %zd: %s\n", cnt, elf_errmsg (-1));
180 exit (1);
181 }
182 }
183 }
184
185 /* Copy all sections, headers and data. */
186 Elf_Scn *scn = NULL;
187 while ((scn = elf_nextscn (elfa, scn)) != NULL)
188 {
189 /* Get the header. */
190 GElf_Shdr shdr;
191 if (gelf_getshdr (scn, &shdr) == NULL)
192 {
193 printf ("couldn't get shdr: %s\n", elf_errmsg (-1));
194 exit (1);
195 }
196
197 /* Create new section. */
198 Elf_Scn *new_scn = elf_newscn (elfb);
199 if (new_scn == NULL)
200 {
201 printf ("couldn't create new section: %s\n", elf_errmsg (-1));
202 exit (1);
203 }
204
205 if (gelf_update_shdr (new_scn, &shdr) == 0)
206 {
207 printf ("couldn't update shdr: %s\n", elf_errmsg (-1));
208 exit (1);
209 }
210
211 /* Copy over section data. */
212 Elf_Data *data = NULL;
213 while ((data = elf_getdata (scn, data)) != NULL)
214 {
215 Elf_Data *new_data = elf_newdata (new_scn);
216 if (new_data == NULL)
217 {
218 printf ("couldn't create new section data: %s\n",
219 elf_errmsg (-1));
220 exit (1);
221 }
222 *new_data = *data;
223 }
224 }
225
226 /* Write everything to disk. If there are any phdrs then we want
227 the exact same layout. Do we want ELF_F_PERMISSIVE? */
228 if (phnum > 0)
229 elf_flagelf (elfb, ELF_C_SET, ELF_F_LAYOUT);
230 if (elf_update (elfb, ELF_C_WRITE) < 0)
231 {
232 printf ("failure in elf_update: %s\n", elf_errmsg (-1));
233 exit (1);
234 }
235
236 if (elf_end (elfa) != 0)
237 {
238 printf ("couldn't cleanup elf '%s': %s\n", in, elf_errmsg (-1));
239 exit (1);
240 }
241
242 if (close (fda) != 0)
243 {
244 printf ("couldn't close '%s': %s\n", in, strerror (errno));
245 exit (1);
246 }
247
248 if (elf_end (elfb) != 0)
249 {
250 printf ("couldn't cleanup elf '%s': %s\n", out, elf_errmsg (-1));
251 exit (1);
252 }
253
254 if (close (fdb) != 0)
255 {
256 printf ("couldn't close '%s': %s\n", out, strerror (errno));
257 exit (1);
258 }
259 }
260
261 int
main(int argc,const char * argv[])262 main (int argc, const char *argv[])
263 {
264 elf_version (EV_CURRENT);
265
266 /* Takes the given file, and create a new identical one. */
267 if (argc < 3 || argc > 4)
268 {
269 fprintf (stderr, "elfcopy [--mmap] in.elf out.elf\n");
270 exit (1);
271 }
272
273 int argn = 1;
274 bool use_mmap = false;
275 if (strcmp (argv[argn], "--mmap") == 0)
276 {
277 use_mmap = true;
278 argn++;
279 }
280
281 const char *in = argv[argn++];
282 const char *out = argv[argn];
283 copy_elf (in, out, use_mmap);
284
285 return 0;
286 }
287