/* Test program for copying a whole ELF file using libelf.
Copyright (C) 2018 Red Hat, Inc.
This file is part of elfutils.
This file is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
elfutils is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include ELFUTILS_HEADER(elf)
#include <gelf.h>
/* shstrndx is special, might overflow into section zero header sh_link. */
static int
setshstrndx (Elf *elf, size_t ndx)
{
printf ("setshstrndx: %zd\n", ndx);
GElf_Ehdr ehdr_mem;
GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
if (ehdr == NULL)
return -1;
if (ndx < SHN_LORESERVE)
ehdr->e_shstrndx = ndx;
else
{
ehdr->e_shstrndx = SHN_XINDEX;
Elf_Scn *zscn = elf_getscn (elf, 0);
GElf_Shdr zshdr_mem;
GElf_Shdr *zshdr = gelf_getshdr (zscn, &zshdr_mem);
if (zshdr == NULL)
return -1;
zshdr->sh_link = ndx;
if (gelf_update_shdr (zscn, zshdr) == 0)
return -1;
}
if (gelf_update_ehdr (elf, ehdr) == 0)
return -1;
return 0;
}
/* Copies all elements of an ELF file either using mmap or read. */
static void
copy_elf (const char *in, const char *out, bool use_mmap, bool reverse_offs)
{
printf ("\ncopy_elf: %s -> %s (%s,%s)\n", in, out,
use_mmap ? "mmap" : "read",
reverse_offs ? "reverse" : "same");
/* Existing ELF file. */
int fda = open (in, O_RDONLY);
if (fda < 0)
{
fprintf (stderr, "Couldn't open file '%s': %s\n",
in, strerror (errno));
exit (1);
}
Elf *elfa = elf_begin (fda, use_mmap ? ELF_C_READ_MMAP : ELF_C_READ, NULL);
if (elfa == NULL)
{
fprintf (stderr, "Couldn't open ELF file '%s': %s\n",
in, elf_errmsg (-1));
exit (1);
}
/* Open new file. */
int fdb = open (out, O_RDWR | O_CREAT | O_TRUNC, 0644);
if (fdb < 0)
{
fprintf (stderr, "Couldn't create file '%s': %s\n",
out, strerror (errno));
exit (1);
}
Elf *elfb = elf_begin (fdb, use_mmap ? ELF_C_WRITE_MMAP : ELF_C_WRITE, NULL);
if (elfb == NULL)
{
fprintf (stderr, "Couldn't create ELF file '%s': %s\n",
out, elf_errmsg (-1));
exit (1);
}
// Copy ELF header.
GElf_Ehdr ehdr_mema;
GElf_Ehdr *ehdra = gelf_getehdr (elfa, &ehdr_mema);
if (ehdra == NULL)
{
printf ("cannot get ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
int class = gelf_getclass (elfa);
// Create an ELF header.
if (gelf_newehdr (elfb, class) == 0)
{
printf ("cannot create ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
/* New elf header is an exact copy. */
GElf_Ehdr ehdr_memb;
GElf_Ehdr *ehdrb = &ehdr_memb;
*ehdrb = *ehdra;
if (gelf_update_ehdr (elfb, ehdrb) == 0)
{
printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
/* shstrndx is special. (Technically phdrnum and shdrnum are also
special, but they are handled by libelf.) */
size_t shstrndx;
if (elf_getshdrstrndx (elfa, &shstrndx) < 0)
{
printf ("cannot get shstrndx: %s\n", elf_errmsg (-1));
exit (1);
}
if (setshstrndx (elfb, shstrndx) < 0)
{
printf ("cannot set shstrndx: %s\n", elf_errmsg (-1));
exit (1);
}
/* If there are phdrs, copy them over. */
size_t phnum;
if (elf_getphdrnum (elfa, &phnum) != 0)
{
printf ("cannot get phdrs: %s\n", elf_errmsg (-1));
exit (1);
}
if (phnum > 0)
{
if (gelf_newphdr (elfb, phnum) == 0)
{
printf ("cannot create phdrs: %s\n", elf_errmsg (-1));
exit (1);
}
for (size_t cnt = 0; cnt < phnum; ++cnt)
{
GElf_Phdr phdr_mem;
GElf_Phdr *phdr = gelf_getphdr (elfa, cnt, &phdr_mem);
if (phdr == NULL)
{
printf ("couldn't get phdr %zd: %s\n", cnt, elf_errmsg (-1));
exit (1);
}
if (gelf_update_phdr (elfb, cnt, phdr) == 0)
{
printf ("couldn't update phdr %zd: %s\n", cnt, elf_errmsg (-1));
exit (1);
}
}
}
GElf_Off *offs = NULL;
size_t shnum;
if (reverse_offs)
{
if (elf_getshdrnum (elfa, &shnum) < 0)
{
printf ("couldn't get shdrnum: %s\n", elf_errmsg (-1));
exit (1);
}
offs = (GElf_Off *) malloc (shnum * sizeof (GElf_Off));
if (offs == NULL)
{
printf ("couldn't allocate memory for offs\n");
exit (1);
}
}
/* Copy all sections, headers and data. */
Elf_Scn *scn = NULL;
size_t last_off = 0;
GElf_Shdr last_shdr = { .sh_type = SHT_NULL };
while ((scn = elf_nextscn (elfa, scn)) != NULL)
{
/* Get the header. */
GElf_Shdr shdr;
if (gelf_getshdr (scn, &shdr) == NULL)
{
printf ("couldn't get shdr: %s\n", elf_errmsg (-1));
exit (1);
}
if (reverse_offs)
{
offs[last_off] = shdr.sh_offset;
if (last_shdr.sh_type != SHT_NULL
&& last_shdr.sh_addralign == shdr.sh_addralign
&& shdr.sh_addralign == 1
&& last_shdr.sh_type != SHT_NOBITS
&& shdr.sh_type != SHT_NOBITS
&& last_shdr.sh_offset + last_shdr.sh_size == shdr.sh_offset
&& (phnum == 0
|| ((shdr.sh_flags & SHF_ALLOC) == 0
&& (last_shdr.sh_flags & SHF_ALLOC) == 0)))
{
printf ("Swapping offsets of section %zd and %zd\n",
last_off, last_off + 1);
GElf_Word off = offs[last_off - 1];
offs[last_off - 1] = off + shdr.sh_size;
offs[last_off] = off;
last_shdr.sh_type = SHT_NULL;
}
else
{
last_shdr = shdr;
offs[last_off] = shdr.sh_offset;
}
last_off++;
}
/* Create new section. */
Elf_Scn *new_scn = elf_newscn (elfb);
if (new_scn == NULL)
{
printf ("couldn't create new section: %s\n", elf_errmsg (-1));
exit (1);
}
if (gelf_update_shdr (new_scn, &shdr) == 0)
{
printf ("couldn't update shdr: %s\n", elf_errmsg (-1));
exit (1);
}
/* Copy over section data. */
Elf_Data *data = NULL;
while ((data = elf_getdata (scn, data)) != NULL)
{
Elf_Data *new_data = elf_newdata (new_scn);
if (new_data == NULL)
{
printf ("couldn't create new section data: %s\n",
elf_errmsg (-1));
exit (1);
}
*new_data = *data;
}
}
if (reverse_offs)
{
last_off = 0;
scn = NULL;
while ((scn = elf_nextscn (elfb, scn)) != NULL)
{
GElf_Shdr shdr;
if (gelf_getshdr (scn, &shdr) == NULL)
{
printf ("couldn't get shdr for updating: %s\n", elf_errmsg (-1));
exit (1);
}
shdr.sh_offset = offs[last_off++];
if (gelf_update_shdr (scn, &shdr) == 0)
{
printf ("couldn't update shdr sh_off: %s\n", elf_errmsg (-1));
exit (1);
}
}
free (offs);
}
/* Write everything to disk. If there are any phdrs, or we want to
update the offsets, then we want the exact same layout. Do we
want ELF_F_PERMISSIVE? */
if (phnum > 0 || reverse_offs)
elf_flagelf (elfb, ELF_C_SET, ELF_F_LAYOUT);
if (elf_update (elfb, ELF_C_WRITE) < 0)
{
printf ("failure in elf_update: %s\n", elf_errmsg (-1));
exit (1);
}
if (elf_end (elfa) != 0)
{
printf ("couldn't cleanup elf '%s': %s\n", in, elf_errmsg (-1));
exit (1);
}
if (close (fda) != 0)
{
printf ("couldn't close '%s': %s\n", in, strerror (errno));
exit (1);
}
if (elf_end (elfb) != 0)
{
printf ("couldn't cleanup elf '%s': %s\n", out, elf_errmsg (-1));
exit (1);
}
if (close (fdb) != 0)
{
printf ("couldn't close '%s': %s\n", out, strerror (errno));
exit (1);
}
}
int
main (int argc, const char *argv[])
{
elf_version (EV_CURRENT);
/* Takes the given file, and create a new identical one. */
if (argc < 3 || argc > 5)
{
fprintf (stderr, "elfcopy [--mmap] [--reverse-offs] in.elf out.elf\n");
exit (1);
}
int argn = 1;
bool use_mmap = false;
if (strcmp (argv[argn], "--mmap") == 0)
{
use_mmap = true;
argn++;
}
bool reverse_offs = false;
if (strcmp (argv[argn], "--reverse-offs") == 0)
{
reverse_offs = true;
argn++;
}
const char *in = argv[argn++];
const char *out = argv[argn];
copy_elf (in, out, use_mmap, reverse_offs);
return 0;
}