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#!/usr/bin/perl
######################################################################
#
# File : split_bootimg.pl
# Author(s) : William Enck <enck@cse.psu.edu>
# Description : Split appart an Android boot image created
# with mkbootimg. The format can be found in
# android-src/system/core/mkbootimg/bootimg.h
#
# Thanks to alansj on xda-developers.com for
# identifying the format in bootimg.h and
# describing initial instructions for splitting
# the boot.img file.
#
# Last Modified : Tue Dec 2 23:36:25 EST 2008
# By : William Enck <enck@cse.psu.edu>
#
# Copyright (c) 2008 William Enck
#
######################################################################
use strict;
use warnings;
# Turn on print flushing
$|++;
######################################################################
## Global Variables and Constants
my $SCRIPT = __FILE__;
my $IMAGE_FN = undef;
# Constants (from bootimg.h)
use constant BOOT_MAGIC => 'ANDROID!';
use constant BOOT_MAGIC_SIZE => 8;
use constant BOOT_NAME_SIZE => 16;
use constant BOOT_ARGS_SIZE => 512;
# Unsigned integers are 4 bytes
use constant UNSIGNED_SIZE => 4;
# Parsed Values
my $PAGE_SIZE = undef;
my $KERNEL_SIZE = undef;
my $RAMDISK_SIZE = undef;
my $SECOND_SIZE = undef;
######################################################################
## Main Code
&parse_cmdline();
&parse_header($IMAGE_FN);
=format (from bootimg.h)
** +-----------------+
** | boot header | 1 page
** +-----------------+
** | kernel | n pages
** +-----------------+
** | ramdisk | m pages
** +-----------------+
** | second stage | o pages
** +-----------------+
**
** n = (kernel_size + page_size - 1) / page_size
** m = (ramdisk_size + page_size - 1) / page_size
** o = (second_size + page_size - 1) / page_size
=cut
my $n = int(($KERNEL_SIZE + $PAGE_SIZE - 1) / $PAGE_SIZE);
my $m = int(($RAMDISK_SIZE + $PAGE_SIZE - 1) / $PAGE_SIZE);
my $o = int(($SECOND_SIZE + $PAGE_SIZE - 1) / $PAGE_SIZE);
my $k_offset = $PAGE_SIZE;
my $r_offset = $k_offset + ($n * $PAGE_SIZE);
my $s_offset = $r_offset + ($m * $PAGE_SIZE);
(my $base = $IMAGE_FN) =~ s/.*\/(.*)$/$1/;
my $k_file = $base . "-kernel";
my $r_file = $base . "-ramdisk.gz";
my $s_file = $base . "-second.gz";
# The kernel is always there
print "Writing $k_file ...";
&dump_file($IMAGE_FN, $k_file, $k_offset, $KERNEL_SIZE);
print " complete.\n";
# The ramdisk is always there
print "Writing $r_file ...";
&dump_file($IMAGE_FN, $r_file, $r_offset, $RAMDISK_SIZE);
print " complete.\n";
# The Second stage bootloader is optional
unless ($SECOND_SIZE == 0) {
print "Writing $s_file ...";
&dump_file($IMAGE_FN, $s_file, $s_offset, $SECOND_SIZE);
print " complete.\n";
}
######################################################################
## Supporting Subroutines
=header_format (from bootimg.h)
struct boot_img_hdr
{
unsigned char magic[BOOT_MAGIC_SIZE];
unsigned kernel_size; /* size in bytes */
unsigned kernel_addr; /* physical load addr */
unsigned ramdisk_size; /* size in bytes */
unsigned ramdisk_addr; /* physical load addr */
unsigned second_size; /* size in bytes */
unsigned second_addr; /* physical load addr */
unsigned tags_addr; /* physical addr for kernel tags */
unsigned page_size; /* flash page size we assume */
unsigned unused[2]; /* future expansion: should be 0 */
unsigned char name[BOOT_NAME_SIZE]; /* asciiz product name */
unsigned char cmdline[BOOT_ARGS_SIZE];
unsigned id[8]; /* timestamp / checksum / sha1 / etc */
};
=cut
sub parse_header {
my ($fn) = @_;
my $buf = undef;
open INF, $fn or die "Could not open $fn: $!\n";
binmode INF;
# Read the Magic
read(INF, $buf, BOOT_MAGIC_SIZE);
unless ($buf eq BOOT_MAGIC) {
die "Android Magic not found in $fn. Giving up.\n";
}
# Read kernel size and address (assume little-endian)
read(INF, $buf, UNSIGNED_SIZE * 2);
my ($k_size, $k_addr) = unpack("VV", $buf);
# Read ramdisk size and address (assume little-endian)
read(INF, $buf, UNSIGNED_SIZE * 2);
my ($r_size, $r_addr) = unpack("VV", $buf);
# Read second size and address (assume little-endian)
read(INF, $buf, UNSIGNED_SIZE * 2);
my ($s_size, $s_addr) = unpack("VV", $buf);
# Ignore tags_addr
read(INF, $buf, UNSIGNED_SIZE);
# get the page size (assume little-endian)
read(INF, $buf, UNSIGNED_SIZE);
my ($p_size) = unpack("V", $buf);
# Ignore unused
read(INF, $buf, UNSIGNED_SIZE * 2);
# Read the name (board name)
read(INF, $buf, BOOT_NAME_SIZE);
my $name = $buf;
# Read the command line
read(INF, $buf, BOOT_ARGS_SIZE);
my $cmdline = $buf;
# Ignore the id
read(INF, $buf, UNSIGNED_SIZE * 8);
# Close the file
close INF;
# Print important values
printf "Page size: %d (0x%08x)\n", $p_size, $p_size;
printf "Kernel size: %d (0x%08x)\n", $k_size, $k_size;
printf "Ramdisk size: %d (0x%08x)\n", $r_size, $r_size;
printf "Second size: %d (0x%08x)\n", $s_size, $s_size;
printf "Board name: $name\n";
printf "Command line: $cmdline\n";
# Save the values
$PAGE_SIZE = $p_size;
$KERNEL_SIZE = $k_size;
$RAMDISK_SIZE = $r_size;
$SECOND_SIZE = $s_size;
}
sub dump_file {
my ($infn, $outfn, $offset, $size) = @_;
my $buf = undef;
open INF, $infn or die "Could not open $infn: $!\n";
open OUTF, ">$outfn" or die "Could not open $outfn: $!\n";
binmode INF;
binmode OUTF;
seek(INF, $offset, 0) or die "Could not seek in $infn: $!\n";
read(INF, $buf, $size) or die "Could not read $infn: $!\n";
print OUTF $buf or die "Could not write $outfn: $!\n";
close INF;
close OUTF;
}
######################################################################
## Configuration Subroutines
sub parse_cmdline {
unless ($#ARGV == 0) {
die "Usage: $SCRIPT boot.img\n";
}
$IMAGE_FN = $ARGV[0];
}
@JPT77

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commented Sep 21, 2017

see my fork https://gist.github.com/JPT77/0a2fc46a8a9926734f52b82ec65197f7 for an update which adds the device tree partition

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