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/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*
* This is a trivial program to edit an ELF file in place, making
* one crucial modification to a program header. It's invoked:
* bootstrap_phdr_hacker FILENAME SEGMENT_NUMBER
* where SEGMENT_NUMBER is the zero-origin index of the program header
* we'll touch. This is a PT_LOAD with p_filesz of zero. We change its
* p_filesz to match its p_memsz value.
*/
#include <errno.h>
#include <error.h>
#include <fcntl.h>
#include <gelf.h>
#include <libelf.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char **argv) {
if (argc != 3)
error(1, 0, "Usage: %s FILENAME SEGMENT_NUMBER", argv[0]);
const char *const file = argv[1];
const int segment = atoi(argv[2]);
int fd = open(file, O_RDWR);
if (fd < 0)
error(2, errno, "Cannot open %s for read/write", file);
if (elf_version(EV_CURRENT) == EV_NONE)
error(2, 0, "elf_version: %s", elf_errmsg(-1));
Elf *elf = elf_begin(fd, ELF_C_RDWR, NULL);
if (elf == NULL)
error(2, 0, "elf_begin: %s", elf_errmsg(-1));
if (elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT) == 0)
error(2, 0, "elf_flagelf: %s", elf_errmsg(-1));
GElf_Phdr phdr;
GElf_Phdr *ph = gelf_getphdr(elf, segment, &phdr);
if (ph == NULL)
error(2, 0, "gelf_getphdr: %s", elf_errmsg(-1));
if (ph->p_type != PT_LOAD)
error(3, 0, "Program header %d is %u, not PT_LOAD",
segment, (unsigned int) ph->p_type);
if (ph->p_filesz != 0)
error(3, 0, "Program header %d has nonzero p_filesz", segment);
ph->p_filesz = ph->p_memsz;
if (gelf_update_phdr(elf, segment, ph) == 0)
error(2, 0, "gelf_update_phdr: %s", elf_errmsg(-1));
if (elf_flagphdr(elf, ELF_C_SET, ELF_F_DIRTY) == 0)
error(2, 0, "elf_flagphdr: %s", elf_errmsg(-1));
if (elf_update(elf, ELF_C_WRITE) < 0)
error(2, 0, "elf_update: %s", elf_errmsg(-1));
close(fd);
return 0;
}
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