1 /* Test program for adding a section to an empty ELF file.
2 Copyright (C) 2016 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 <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <unistd.h>
30 #include "system.h"
31
32 #include ELFUTILS_HEADER(elf)
33 #include <gelf.h>
34
35
36 /* Index of last string added. Returned by add_string (). */
37 static size_t stridx = 0;
38
39 /* Adds a string and returns the offset in the section. */
40 static size_t
add_string(Elf_Scn * scn,char * str)41 add_string (Elf_Scn *scn, char *str)
42 {
43 size_t lastidx = stridx;
44 size_t size = strlen (str) + 1;
45
46 Elf_Data *data = elf_newdata (scn);
47 if (data == NULL)
48 {
49 printf ("cannot create data SHSTRTAB section: %s\n", elf_errmsg (-1));
50 exit (1);
51 }
52
53 data->d_buf = str;
54 data->d_type = ELF_T_BYTE;
55 data->d_size = size;
56 data->d_align = 1;
57 data->d_version = EV_CURRENT;
58
59 stridx += size;
60 printf ("add_string: '%s', stridx: %zd, lastidx: %zd\n",
61 str, stridx, lastidx);
62 return lastidx;
63 }
64
65 static void
check_elf(const char * fname,int class,int use_mmap)66 check_elf (const char *fname, int class, int use_mmap)
67 {
68 printf ("\nfname: %s\n", fname);
69 stridx = 0; // Reset strtab strings index
70
71 int fd = open (fname, O_RDWR | O_CREAT | O_TRUNC, DEFFILEMODE);
72 if (fd == -1)
73 {
74 printf ("cannot open `%s': %s\n", fname, strerror (errno));
75 exit (1);
76 }
77
78 Elf *elf = elf_begin (fd, use_mmap ? ELF_C_WRITE_MMAP : ELF_C_WRITE, NULL);
79 if (elf == NULL)
80 {
81 printf ("cannot create ELF descriptor: %s\n", elf_errmsg (-1));
82 exit (1);
83 }
84
85 // Create an ELF header.
86 if (gelf_newehdr (elf, class) == 0)
87 {
88 printf ("cannot create ELF header: %s\n", elf_errmsg (-1));
89 exit (1);
90 }
91
92 GElf_Ehdr ehdr_mem;
93 GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
94 if (ehdr == NULL)
95 {
96 printf ("cannot get ELF header: %s\n", elf_errmsg (-1));
97 exit (1);
98 }
99
100 // Initialize header.
101 ehdr->e_ident[EI_DATA] = class == ELFCLASS64 ? ELFDATA2LSB : ELFDATA2MSB;
102 ehdr->e_ident[EI_OSABI] = ELFOSABI_GNU;
103 ehdr->e_type = ET_NONE;
104 ehdr->e_machine = EM_X86_64;
105 ehdr->e_version = EV_CURRENT;
106
107 if (gelf_update_ehdr (elf, ehdr) == 0)
108 {
109 printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
110 exit (1);
111 }
112
113 // Write everything to disk.
114 if (elf_update (elf, ELF_C_WRITE) < 0)
115 {
116 printf ("failure in elf_update(WRITE): %s\n", elf_errmsg (-1));
117 exit (1);
118 }
119
120 if (elf_end (elf) != 0)
121 {
122 printf ("failure in elf_end: %s\n", elf_errmsg (-1));
123 exit (1);
124 }
125
126 close (fd);
127
128 /* Reread the ELF from disk now. */
129 fd = open (fname, O_RDWR);
130 if (fd == -1)
131 {
132 printf ("cannot (re)open `%s': %s\n", fname, strerror (errno));
133 exit (1);
134 }
135
136 elf = elf_begin (fd, use_mmap ? ELF_C_RDWR_MMAP : ELF_C_RDWR, NULL);
137 if (elf == NULL)
138 {
139 printf ("cannot create ELF descriptor read-only: %s\n", elf_errmsg (-1));
140 exit (1);
141 }
142
143 // There are no sections yet.
144 if (elf_nextscn (elf, NULL) != NULL)
145 {
146 printf ("Empty elf had a section???\n");
147 exit (1);
148 }
149
150 // Create strtab section.
151 Elf_Scn *scn = elf_newscn (elf);
152 if (scn == NULL)
153 {
154 printf ("cannot create strings section: %s\n", elf_errmsg (-1));
155 exit (1);
156 }
157
158 // Add an empty string to the table as NUL entry for section zero.
159 add_string (scn, "");
160
161 GElf_Shdr shdr_mem;
162 GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
163 if (shdr == NULL)
164 {
165 printf ("cannot get header for strings section: %s\n", elf_errmsg (-1));
166 exit (1);
167 }
168
169 shdr->sh_type = SHT_STRTAB;
170 shdr->sh_flags = 0;
171 shdr->sh_addr = 0;
172 shdr->sh_link = SHN_UNDEF;
173 shdr->sh_info = SHN_UNDEF;
174 shdr->sh_addralign = 1;
175 shdr->sh_entsize = 0;
176 shdr->sh_name = add_string (scn, ".strtab");
177
178 // We have to store the section strtab index in the ELF header.
179 // So sections have actual names.
180 int ndx = elf_ndxscn (scn);
181 ehdr->e_shstrndx = ndx;
182
183 if (gelf_update_ehdr (elf, ehdr) == 0)
184 {
185 printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
186 exit (1);
187 }
188
189 // Finished strtab section, update the header.
190 if (gelf_update_shdr (scn, shdr) == 0)
191 {
192 printf ("cannot update STRTAB section header: %s\n", elf_errmsg (-1));
193 exit (1);
194 }
195
196 // Write everything to disk.
197 if (elf_update (elf, ELF_C_WRITE) < 0)
198 {
199 printf ("failure in elf_update(WRITE): %s\n", elf_errmsg (-1));
200 exit (1);
201 }
202
203 if (elf_end (elf) != 0)
204 {
205 printf ("failure in elf_end: %s\n", elf_errmsg (-1));
206 exit (1);
207 }
208
209 close (fd);
210
211 // And read it in one last time.
212 fd = open (fname, O_RDONLY);
213 if (fd == -1)
214 {
215 printf ("cannot open `%s' read-only: %s\n", fname, strerror (errno));
216 exit (1);
217 }
218
219 elf = elf_begin (fd, use_mmap ? ELF_C_READ_MMAP : ELF_C_READ, NULL);
220 if (elf == NULL)
221 {
222 printf ("cannot create ELF descriptor read-only: %s\n", elf_errmsg (-1));
223 exit (1);
224 }
225
226 // Is our new section there?
227 scn = elf_nextscn (elf, NULL);
228 if (scn == NULL)
229 {
230 printf ("cannot get new section: %s\n", elf_errmsg (-1));
231 exit (1);
232 }
233
234 shdr = gelf_getshdr (scn, &shdr_mem);
235 if (shdr == NULL)
236 {
237 printf ("cannot get header for new section: %s\n", elf_errmsg (-1));
238 exit (1);
239 }
240
241 size_t shstrndx;
242 if (elf_getshdrstrndx (elf, &shstrndx) < 0)
243 {
244 printf ("elf_getshdrstrndx: %s\n", elf_errmsg (-1));
245 exit (1);
246 }
247
248 const char *sname = elf_strptr (elf, shstrndx, shdr->sh_name);
249 if (sname == NULL || strcmp (sname, ".strtab") != 0)
250 {
251 printf ("Bad section name: %s\n", sname);
252 exit (1);
253 }
254
255 if (elf_end (elf) != 0)
256 {
257 printf ("failure in elf_end: %s\n", elf_errmsg (-1));
258 exit (1);
259 }
260
261 close (fd);
262
263 unlink (fname);
264 }
265
266 int
main(int argc,char * argv[])267 main (int argc __attribute__ ((unused)),
268 char *argv[] __attribute__ ((unused)))
269 {
270 elf_version (EV_CURRENT);
271
272 check_elf ("empty.elf.32", ELFCLASS32, 0);
273 check_elf ("empty.elf.32.mmap", ELFCLASS32, 1);
274 check_elf ("empty.elf.64", ELFCLASS64, 0);
275 check_elf ("empty.elf.64.mmap", ELFCLASS64, 1);
276
277 return 0;
278 }
279