/* Test program for adding a section to an empty ELF file.
Copyright (C) 2016 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include ELFUTILS_HEADER(elf)
#include <gelf.h>
/* Index of last string added. Returned by add_string (). */
static size_t stridx = 0;
/* Adds a string and returns the offset in the section. */
static size_t
add_string (Elf_Scn *scn, char *str)
{
size_t lastidx = stridx;
size_t size = strlen (str) + 1;
Elf_Data *data = elf_newdata (scn);
if (data == NULL)
{
printf ("cannot create data SHSTRTAB section: %s\n", elf_errmsg (-1));
exit (1);
}
data->d_buf = str;
data->d_type = ELF_T_BYTE;
data->d_size = size;
data->d_align = 1;
data->d_version = EV_CURRENT;
stridx += size;
printf ("add_string: '%s', stridx: %zd, lastidx: %zd\n",
str, stridx, lastidx);
return lastidx;
}
static void
check_elf (const char *fname, int class, int use_mmap)
{
printf ("\nfname: %s\n", fname);
stridx = 0; // Reset strtab strings index
int fd = open (fname, O_RDWR | O_CREAT | O_TRUNC, 0666);
if (fd == -1)
{
printf ("cannot open `%s': %s\n", fname, strerror (errno));
exit (1);
}
Elf *elf = elf_begin (fd, use_mmap ? ELF_C_WRITE_MMAP : ELF_C_WRITE, NULL);
if (elf == NULL)
{
printf ("cannot create ELF descriptor: %s\n", elf_errmsg (-1));
exit (1);
}
// Create an ELF header.
if (gelf_newehdr (elf, class) == 0)
{
printf ("cannot create ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
GElf_Ehdr ehdr_mem;
GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
if (ehdr == NULL)
{
printf ("cannot get ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
// Initialize header.
ehdr->e_ident[EI_DATA] = class == ELFCLASS64 ? ELFDATA2LSB : ELFDATA2MSB;
ehdr->e_ident[EI_OSABI] = ELFOSABI_GNU;
ehdr->e_type = ET_NONE;
ehdr->e_machine = EM_X86_64;
ehdr->e_version = EV_CURRENT;
if (gelf_update_ehdr (elf, ehdr) == 0)
{
printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
// Write everything to disk.
if (elf_update (elf, ELF_C_WRITE) < 0)
{
printf ("failure in elf_update(WRITE): %s\n", elf_errmsg (-1));
exit (1);
}
if (elf_end (elf) != 0)
{
printf ("failure in elf_end: %s\n", elf_errmsg (-1));
exit (1);
}
close (fd);
/* Reread the ELF from disk now. */
fd = open (fname, O_RDWR, 0666);
if (fd == -1)
{
printf ("cannot (re)open `%s': %s\n", fname, strerror (errno));
exit (1);
}
elf = elf_begin (fd, use_mmap ? ELF_C_RDWR_MMAP : ELF_C_RDWR, NULL);
if (elf == NULL)
{
printf ("cannot create ELF descriptor read-only: %s\n", elf_errmsg (-1));
exit (1);
}
// There are no sections yet.
if (elf_nextscn (elf, NULL) != NULL)
{
printf ("Empty elf had a section???\n");
exit (1);
}
// Create strtab section.
Elf_Scn *scn = elf_newscn (elf);
if (scn == NULL)
{
printf ("cannot create strings section: %s\n", elf_errmsg (-1));
exit (1);
}
// Add an empty string to the table as NUL entry for section zero.
add_string (scn, "");
GElf_Shdr shdr_mem;
GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
if (shdr == NULL)
{
printf ("cannot get header for strings section: %s\n", elf_errmsg (-1));
exit (1);
}
shdr->sh_type = SHT_STRTAB;
shdr->sh_flags = 0;
shdr->sh_addr = 0;
shdr->sh_link = SHN_UNDEF;
shdr->sh_info = SHN_UNDEF;
shdr->sh_addralign = 1;
shdr->sh_entsize = 0;
shdr->sh_name = add_string (scn, ".strtab");
// We have to store the section strtab index in the ELF header.
// So sections have actual names.
int ndx = elf_ndxscn (scn);
ehdr->e_shstrndx = ndx;
if (gelf_update_ehdr (elf, ehdr) == 0)
{
printf ("cannot update ELF header: %s\n", elf_errmsg (-1));
exit (1);
}
// Finished strtab section, update the header.
if (gelf_update_shdr (scn, shdr) == 0)
{
printf ("cannot update STRTAB section header: %s\n", elf_errmsg (-1));
exit (1);
}
// Write everything to disk.
if (elf_update (elf, ELF_C_WRITE) < 0)
{
printf ("failure in elf_update(WRITE): %s\n", elf_errmsg (-1));
exit (1);
}
if (elf_end (elf) != 0)
{
printf ("failure in elf_end: %s\n", elf_errmsg (-1));
exit (1);
}
close (fd);
// And read it in one last time.
fd = open (fname, O_RDONLY, 0666);
if (fd == -1)
{
printf ("cannot open `%s' read-only: %s\n", fname, strerror (errno));
exit (1);
}
elf = elf_begin (fd, use_mmap ? ELF_C_READ_MMAP : ELF_C_READ, NULL);
if (elf == NULL)
{
printf ("cannot create ELF descriptor read-only: %s\n", elf_errmsg (-1));
exit (1);
}
// Is our new section there?
scn = elf_nextscn (elf, NULL);
if (scn == NULL)
{
printf ("cannot get new section: %s\n", elf_errmsg (-1));
exit (1);
}
shdr = gelf_getshdr (scn, &shdr_mem);
if (shdr == NULL)
{
printf ("cannot get header for new section: %s\n", elf_errmsg (-1));
exit (1);
}
size_t shstrndx;
if (elf_getshdrstrndx (elf, &shstrndx) < 0)
{
printf ("elf_getshdrstrndx: %s\n", elf_errmsg (-1));
exit (1);
}
const char *sname = elf_strptr (elf, shstrndx, shdr->sh_name);
if (sname == NULL || strcmp (sname, ".strtab") != 0)
{
printf ("Bad section name: %s\n", sname);
exit (1);
}
if (elf_end (elf) != 0)
{
printf ("failure in elf_end: %s\n", elf_errmsg (-1));
exit (1);
}
close (fd);
unlink (fname);
}
int
main (int argc __attribute__ ((unused)),
char *argv[] __attribute__ ((unused)))
{
elf_version (EV_CURRENT);
check_elf ("empty.elf.32", ELFCLASS32, 0);
check_elf ("empty.elf.32.mmap", ELFCLASS32, 1);
check_elf ("empty.elf.64", ELFCLASS64, 0);
check_elf ("empty.elf.64.mmap", ELFCLASS64, 1);
return 0;
}