xref: /third_party/elfutils/tests/elfcopy.c (revision da0c48c4) 
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.  */
39static int
40setshstrndx (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.  */
71static void
72copy_elf (const char *in, const char *out, bool use_mmap, bool reverse_offs)
73{
74  printf ("\ncopy_elf: %s -> %s (%s,%s)\n", in, out,
75	  use_mmap ? "mmap" : "read",
76	  reverse_offs ? "reverse" : "same");
77
78  /* Existing ELF file.  */
79  int fda = open (in, O_RDONLY);
80  if (fda < 0)
81    {
82      fprintf (stderr, "Couldn't open file '%s': %s\n",
83	       in, strerror (errno));
84      exit (1);
85    }
86
87  Elf *elfa = elf_begin (fda, use_mmap ? ELF_C_READ_MMAP : ELF_C_READ, NULL);
88  if (elfa == NULL)
89    {
90      fprintf (stderr, "Couldn't open ELF file '%s': %s\n",
91	       in, elf_errmsg (-1));
92      exit (1);
93    }
94
95  /* Open new file.  */
96  int fdb = open (out, O_RDWR | O_CREAT | O_TRUNC, 0644);
97  if (fdb < 0)
98    {
99      fprintf (stderr, "Couldn't create file '%s': %s\n",
100	       out, strerror (errno));
101      exit (1);
102    }
103
104  Elf *elfb = elf_begin (fdb, use_mmap ? ELF_C_WRITE_MMAP : ELF_C_WRITE, NULL);
105  if (elfb == NULL)
106    {
107      fprintf (stderr, "Couldn't create ELF file '%s': %s\n",
108	       out, elf_errmsg (-1));
109      exit (1);
110    }
111
112  // Copy ELF header.
113  GElf_Ehdr ehdr_mema;
114  GElf_Ehdr *ehdra = gelf_getehdr (elfa, &ehdr_mema);
115  if (ehdra == NULL)
116    {
117      printf ("cannot get ELF header: %s\n", elf_errmsg (-1));
118      exit (1);
119    }
120
121  int class = gelf_getclass (elfa);
122  // Create an ELF header.
123  if (gelf_newehdr (elfb, class) == 0)
124    {
125      printf ("cannot create ELF header: %s\n", elf_errmsg (-1));
126      exit (1);
127    }
128
129  /* New elf header is an exact copy.  */
130  GElf_Ehdr ehdr_memb;
131  GElf_Ehdr *ehdrb = &ehdr_memb;
132  *ehdrb = *ehdra;
133  if (gelf_update_ehdr (elfb, ehdrb) == 0)
134    {
135      printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
136      exit (1);
137    }
138
139  /* shstrndx is special.  (Technically phdrnum and shdrnum are also
140     special, but they are handled by libelf.)  */
141  size_t shstrndx;
142  if (elf_getshdrstrndx (elfa, &shstrndx) < 0)
143    {
144      printf ("cannot get shstrndx: %s\n", elf_errmsg (-1));
145      exit (1);
146    }
147  if (setshstrndx (elfb, shstrndx) < 0)
148    {
149      printf ("cannot set shstrndx: %s\n", elf_errmsg (-1));
150      exit (1);
151    }
152
153  /* If there are phdrs, copy them over.  */
154  size_t phnum;
155  if (elf_getphdrnum (elfa, &phnum) != 0)
156    {
157      printf ("cannot get phdrs: %s\n", elf_errmsg (-1));
158      exit (1);
159    }
160
161  if (phnum > 0)
162    {
163      if (gelf_newphdr (elfb, phnum) == 0)
164	{
165	  printf ("cannot create phdrs: %s\n", elf_errmsg (-1));
166	  exit (1);
167	}
168
169      for (size_t cnt = 0; cnt < phnum; ++cnt)
170	{
171	  GElf_Phdr phdr_mem;
172	  GElf_Phdr *phdr = gelf_getphdr (elfa, cnt, &phdr_mem);
173	  if (phdr == NULL)
174	    {
175	      printf ("couldn't get phdr %zd: %s\n", cnt, elf_errmsg (-1));
176	      exit (1);
177	    }
178
179	  if (gelf_update_phdr (elfb, cnt, phdr) == 0)
180	    {
181	      printf ("couldn't update phdr %zd: %s\n", cnt, elf_errmsg (-1));
182	      exit (1);
183	    }
184	}
185    }
186
187  GElf_Off *offs = NULL;
188  size_t shnum;
189  if (reverse_offs)
190    {
191      if (elf_getshdrnum (elfa, &shnum) < 0)
192	{
193	  printf ("couldn't get shdrnum: %s\n", elf_errmsg (-1));
194	  exit (1);
195	}
196
197      offs = malloc (shnum * sizeof (GElf_Off));
198      if (offs == NULL)
199	{
200	  printf ("couldn't allocate memory for offs\n");
201	  exit (1);
202	}
203    }
204
205  /* Copy all sections, headers and data.  */
206  Elf_Scn *scn = NULL;
207  size_t last_off = 0;
208  GElf_Shdr last_shdr = { .sh_type = SHT_NULL };
209  while ((scn = elf_nextscn (elfa, scn)) != NULL)
210    {
211      /* Get the header.  */
212      GElf_Shdr shdr;
213      if (gelf_getshdr (scn, &shdr) == NULL)
214	{
215	  printf ("couldn't get shdr: %s\n", elf_errmsg (-1));
216	  exit (1);
217	}
218
219      if (reverse_offs)
220	{
221	  offs[last_off] = shdr.sh_offset;
222
223	  if (last_shdr.sh_type != SHT_NULL
224	      && last_shdr.sh_addralign == shdr.sh_addralign
225	      && shdr.sh_addralign == 1
226	      && last_shdr.sh_type != SHT_NOBITS
227	      && shdr.sh_type != SHT_NOBITS
228	      && last_shdr.sh_offset + last_shdr.sh_size == shdr.sh_offset
229	      && (phnum == 0
230		  || ((shdr.sh_flags & SHF_ALLOC) == 0
231		      && (last_shdr.sh_flags & SHF_ALLOC) == 0)))
232	    {
233	      printf ("Swapping offsets of section %zd and %zd\n",
234		      last_off, last_off + 1);
235	      GElf_Word off = offs[last_off - 1];
236	      offs[last_off - 1] = off + shdr.sh_size;
237	      offs[last_off] = off;
238	      last_shdr.sh_type = SHT_NULL;
239	    }
240	  else
241	    {
242	      last_shdr = shdr;
243	      offs[last_off] = shdr.sh_offset;
244	    }
245	  last_off++;
246	}
247
248      /* Create new section.  */
249      Elf_Scn *new_scn = elf_newscn (elfb);
250      if (new_scn == NULL)
251	{
252	  printf ("couldn't create new section: %s\n", elf_errmsg (-1));
253	  exit (1);
254	}
255
256      if (gelf_update_shdr (new_scn, &shdr) == 0)
257	{
258	  printf ("couldn't update shdr: %s\n", elf_errmsg (-1));
259	  exit (1);
260	}
261
262      /* Copy over section data.  */
263      Elf_Data *data = NULL;
264      while ((data = elf_getdata (scn, data)) != NULL)
265	{
266	  Elf_Data *new_data = elf_newdata (new_scn);
267	  if (new_data == NULL)
268	    {
269	      printf ("couldn't create new section data: %s\n",
270		      elf_errmsg (-1));
271	      exit (1);
272	    }
273	  *new_data = *data;
274	}
275    }
276
277  if (reverse_offs)
278    {
279      last_off = 0;
280      scn = NULL;
281      while ((scn = elf_nextscn (elfb, scn)) != NULL)
282	{
283	  GElf_Shdr shdr;
284	  if (gelf_getshdr (scn, &shdr) == NULL)
285	    {
286	      printf ("couldn't get shdr for updating: %s\n", elf_errmsg (-1));
287	      exit (1);
288	    }
289
290	  shdr.sh_offset = offs[last_off++];
291
292	  if (gelf_update_shdr (scn, &shdr) == 0)
293	    {
294	      printf ("couldn't update shdr sh_off: %s\n", elf_errmsg (-1));
295	      exit (1);
296	    }
297	}
298      free (offs);
299    }
300
301  /* Write everything to disk.  If there are any phdrs, or we want to
302     update the offsets, then we want the exact same layout.  Do we
303     want ELF_F_PERMISSIVE?  */
304  if (phnum > 0 || reverse_offs)
305    elf_flagelf (elfb, ELF_C_SET, ELF_F_LAYOUT);
306  if (elf_update (elfb, ELF_C_WRITE) < 0)
307    {
308      printf ("failure in elf_update: %s\n", elf_errmsg (-1));
309      exit (1);
310    }
311
312  if (elf_end (elfa) != 0)
313    {
314      printf ("couldn't cleanup elf '%s': %s\n", in, elf_errmsg (-1));
315      exit (1);
316    }
317
318  if (close (fda) != 0)
319    {
320      printf ("couldn't close '%s': %s\n", in, strerror (errno));
321      exit (1);
322    }
323
324  if (elf_end (elfb) != 0)
325    {
326      printf ("couldn't cleanup elf '%s': %s\n", out, elf_errmsg (-1));
327      exit (1);
328    }
329
330  if (close (fdb) != 0)
331    {
332      printf ("couldn't close '%s': %s\n", out, strerror (errno));
333      exit (1);
334    }
335}
336
337int
338main (int argc, const char *argv[])
339{
340  elf_version (EV_CURRENT);
341
342  /* Takes the given file, and create a new identical one.  */
343  if (argc < 3 || argc > 5)
344    {
345      fprintf (stderr, "elfcopy [--mmap] [--reverse-offs] in.elf out.elf\n");
346      exit (1);
347    }
348
349  int argn = 1;
350  bool use_mmap = false;
351  if (strcmp (argv[argn], "--mmap") == 0)
352    {
353      use_mmap = true;
354      argn++;
355    }
356
357  bool reverse_offs = false;
358  if (strcmp (argv[argn], "--reverse-offs") == 0)
359    {
360      reverse_offs = true;
361      argn++;
362    }
363
364  const char *in = argv[argn++];
365  const char *out = argv[argn];
366  copy_elf (in, out, use_mmap, reverse_offs);
367
368  return 0;
369}
370