Android: 커널에서 램디스크 추출

unpack-bootimg.pl (./unpack-bootimg.pl boot.img)

#!/usr/bin/perl -W

use strict;

use bytes;

use File::Path;

die "did not specify boot img file\n" unless $ARGV[0]; // 부트 이미지를 설정하지 않았을 경우

my $bootimgfile = $ARGV[0];

my $slurpvar = $/;

undef $/;

open (BOOTIMGFILE, "$bootimgfile") or die "could not open boot img file: $bootimgfile\n";

my $bootimg = <BOOTIMGFILE>;

close BOOTIMGFILE;

$/ = $slurpvar;

# chop off the header

$bootimg = substr($bootimg,2048); // 2k 헤더를 잘라내는 과정

# we'll check how many ramdisks are embedded in this image

my $numfiles = 0;

# we look for the hex 00 00 00 00 1F 8B because we expect some trailing padding zeroes from the kernel or previous ramdisk, followed by 1F 8B (the gzip magic number) // 00이 반복되다가 gzip의 매직 넘버인 1F 8B를 찾는 부분

while ($bootimg =~ m/\x00\x00\x00\x00\x1F\x8B/g) {

$numfiles++;

}

if ($numfiles == 0) {

die "Could not find any embedded ramdisk images. Are you sure this is a full boot image?\n"; // 압축되있는 램디스크를 못 찾았을 경우 중지

} elsif ($numfiles > 1) {

die "Found a secondary file after the ramdisk image.  According to the spec (mkbootimg.h) this file can exist, but this script is not designed to deal with this scenario.\n"; // 램디스크 뒤에 따라오는 secondary file을 발견했을 때 중지

}

$bootimg =~ /(.*\x00\x00\x00\x00)(\x1F\x8B.*)/s;

my $kernel = $1;

my $ramdisk = $2;

open (KERNELFILE, ">$ARGV[0]-kernel.gz");

print KERNELFILE $kernel or die;

close KERNELFILE;

open (RAMDISKFILE, ">$ARGV[0]-ramdisk.cpio.gz");

print RAMDISKFILE $ramdisk or die;

close RAMDISKFILE;

print "\nkernel written to $ARGV[0]-kernel.gz\nramdisk written to $ARGV[0]-ramdisk.cpio.gz\n";

if (-e "$ARGV[0]-ramdisk") { 

rmtree "$ARGV[0]-ramdisk";

print "\nremoved old directory $ARGV[0]-ramdisk\n";

}

mkdir "$ARGV[0]-ramdisk" or die;

chdir "$ARGV[0]-ramdisk" or die;

system ("gunzip -c ../$ARGV[0]-ramdisk.cpio.gz | cpio -i");

print "\nextracted ramdisk contents to directory $ARGV[0]-ramdisk/\n";

// 커널을 컴파일 때까지 리팩할 필요가 없다면 차라리 도중에 생기는 gzip 압축파일과 cpio 압축파일 등을 삭제하는 스크립트를 아래 적어도 무방

 repack-bootimg.pl

#!/usr/bin/perl -W

use strict;

use Cwd;

my $dir = getcwd;

my $usage = "repack-bootimg.pl <kernel> <ramdisk-directory> <outfile>\n";

die $usage unless $ARGV[0] && $ARGV[1] && $ARGV[2];

chdir $ARGV[1] or die "$ARGV[1] $!";

system ("find . | cpio -o -H newc | gzip > $dir/ramdisk-repack.cpio.gz");

chdir $dir or die "$ARGV[1] $!";;

# Parameters for Toshiba Folio 100 only

system ("mkbootimg --cmdline 'mem=448M\x400M nvmem=64M\x40448M vmalloc=192M video=tegrafb console=ttyS0,115200n8 usbcore.old_scheme_first=1 tegraboot=sdmmc tegrapart=recovery:122000:a00:800,linux:a0e00:1000:800,loader:300:400:800,mbr:700:200:800,system:900:20000:800,cache:20900:80000:800,misc:a0900:400:800,userdata:a1f00:80000:800 boardtype=PR' --kernel $ARGV[0] --ramdisk ramdisk-repack.cpio.gz -o $ARGV[2]");

unlink("ramdisk-repack.cpio.gz") or die $!;

print "\nrepacked boot image written at $ARGV[1]-repack.img\n";

mkbootfs

mkbootimg

램디스크는 수정한 후 커널을 컴파일할 때 한번에 리팩하면 편합니다.