unpack.sh

#!/bin/bash
# This is an update version of the script found at 
# http://forum.xda-developers.com/wiki/index.php?title=Extract_initramfs_from_zImage
#
# The problem with that script is that the gzip magic number occasionally occur 
# naturally, meaning that some non-compressed files get uncompressed.

# PLATFORM DETECTION

if [[ "$OSTYPE" =~ ^darwin ]]; then
    PLATFORM="darwin"

    # Ensure we have a reasonable grep version. grep < 2.12 on OS X reports bad byte positions.
    grep_ver_major_min="2"
    grep_ver_minor_min="12"
    grep_ver=$(grep -V | head -1 | tr " " "\n" | grep -P "[0-9]" | tr "." "\n")
    grep_ver_major=$(echo "$grep_ver" | head -1)
    grep_ver_minor=$(echo "$grep_ver" | head -2 | tail -1)
    if [ "$grep_ver_major" -eq "$grep_ver_major_min" -a "$grep_ver_minor" -lt "$grep_ver_minor_min" -o "$grep_ver_major" -lt "$grep_ver_major_min" ]; then
        echo "grep version < 2.15, upgrade via 'sudo port install grep'" && exit 1
    fi

    # cut needs locale set to avoid "illegal byte sequence" error
    export LC_ALL=C

    # os x stat uses -f %z to get size
    STATSIZE='stat -f %z'

    # Ensure we have gnucpio
    if [ -z `which gnucpio` ]; then
        echo "gnucpio is required, install via 'sudo port install cpio'" && exit 1
    fi
    CPIO=gnucpio

else

    # TODO: defaults to Linux. We should detect other platforms.
    PLATFORM="linux"

    # standard gnu stat uses -c %s to get size
    STATSIZE='stat -c %s'

    CPIO=cpio
fi

CURRENT_DIR=`pwd`
TEMP_DIR=$CURRENT_DIR/unpack_kernel_tmp
KERNEL_FILE=kernel
KERNEL_GZIP_FILE=kernel.gz
KERNEL_LZMA_FILE=kernel.lzma
KERNEL_XZ_FILE=kernel.xz
KERNEL_LZO_FILE=kernel.lzo
INITRAMFS_FILE=initramfs.cpio
INITRAMFS_DIR=initramfs_root

# DO NOT MODIFY BELOW THIS LINE
[ -z $1 ] && exit 1 || zImage=$1
[ ! -e $1 ] && exit 1
[ -z $2 ] || INITRAMFS_DIR=$2
[ -d $TEMP_DIR ] || `mkdir $TEMP_DIR`

PAYLOAD_DIR=$INITRAMFS_DIR/.payload
RECOVERY_TAR=$TEMP_DIR/recovery.tar
BOOT_TAR=$TEMP_DIR/boot.tar

C_H1="\033[1;36m" # highlight text 1
C_ERR="\033[1;31m"
C_CLEAR="\033[1;0m"

printhl() {
	printf "${C_H1}[I] ${1}${C_CLEAR} \n"
}

printerr() {
	printf "${C_ERR}[E] ${1}${C_CLEAR} \n"
}

function pre_clean()
{
    [ -e $INITRAMFS_FILE ] && rm -f $INITRAMFS_FILE
    [ -e $INITRAMFS_DIR ] && rm -rf $INITRAMFS_DIR
}
function unpack_kernel()
{
    # test Compressed format
    pos1=`grep -P -a -b -m 1 --only-matching '\x1F\x8B\x08' $zImage | \
	cut -f 1 -d : 2>/dev/null | awk '(int($0)<50000){print $0;exit}'`
    pos2=`grep -P -a -b -m 1 --only-matching '\x{5D}\x{00}\x..\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}' \
	$zImage | cut -f 1 -d : 2>/dev/null | awk '(int($0)<50000){print $0;exit}'`
    pos3=`grep -P -a -b -m 1 --only-matching '\xFD\x37\x7A\x58\x5A' $zImage | \
	cut -f 1 -d : 2>/dev/null | tail -1 | awk '(int($0)<50000){print $0;exit}'`
    pos4=`grep -P -a -b --only-matching '\211\114\132' $zImage | head -2 | \
	tail -1 | cut -f 1 -d : 2>/dev/null | awk '(int($0)<50000){print $0;exit}'`

    zImagesize=$($STATSIZE $zImage)

    [ -z $pos1 ] && pos1=$zImagesize
    [ -z $pos2 ] && pos2=$zImagesize
    [ -z $pos3 ] && pos3=$zImagesize
    [ -z $pos4 ] && pos4=$zImagesize

    minpos=`echo -e "$pos1\n$pos2\n$pos3\n$pos4" | sort -n | head -1`
    if [ $minpos -eq $zImagesize ]; then
        printhl "$zImage is an uncompressed kernel image"
        cp "$zImage" "$TEMP_DIR/$KERNEL_FILE"
    elif [ $minpos -eq $pos1 ]; then
        ungzip_kernel
    elif [ $minpos -eq $pos2 ]; then
	unlzma_kernel
    elif [ $minpos -eq $pos3 ]; then
	unxz_kernel
    elif [ $minpos -eq $pos4 ]; then
	unlzo_kernel
    fi
}

function ungzip_kernel()
{
    printhl "Extracting gzip'd kernel image from file: $zImage (start = $pos1)"
    dd if=$zImage of=$TEMP_DIR/$KERNEL_GZIP_FILE bs=$pos1 skip=1 2>/dev/null >/dev/null
    gunzip -qf $TEMP_DIR/$KERNEL_GZIP_FILE
}

function unlzma_kernel()
{
    printhl "Extracting lzma'd kernel image from file: $zImage (start = $pos2)"
    dd if=$zImage of=$TEMP_DIR/$KERNEL_LZMA_FILE bs=$pos2 skip=1 2>/dev/null >/dev/null
	#unlzma -qf $TEMP_DIR/$KERNEL_GZIP_FILE
    unlzma -dqc $TEMP_DIR/$KERNEL_LZMA_FILE > $TEMP_DIR/$KERNEL_FILE 2>/dev/null
}

function unxz_kernel()
{
    printhl "Extracting xz'd kernel image from file: $zImage (start = $pos3)"
    dd status=noxfer if=$zImage bs=$pos3 skip=1 2>/dev/null | unxz -qf > $TEMP_DIR/$KERNEL_FILE 2>/dev/null  
}

function unlzo_kernel()
{
    printhl "Extracting lzo'd kernel image from file: $zImage (start = $pos4)"
    dd if=$zImage of=$TEMP_DIR/$KERNEL_LZO_FILE bs=$pos4 skip=1 2>/dev/null >/dev/null
    lzop -d $TEMP_DIR/$KERNEL_LZO_FILE 2>/dev/null >/dev/null
}

function search_cpio()
{
    for x in none gzip bzip lzma lzo; do
        case $x in
            bzip)
                csig='\x{31}\x{41}\x{59}\x{26}\x{53}\x{59}'
                ucmd='bunzip2 -q'
                fext='.bz2'
                ;;

            gzip)
                csig='\x1F\x8B\x08'
                ucmd='gunzip -q'
                fext='.gz'
                ;;

            lzma)
                csig='\x{5D}\x{00}\x..\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}'
                ucmd='unlzma -q'
                fext='.lzma'
                ;;
            
            lzo)
            	csig='\211\114\132'
            	ucmd='lzop -d'
            	fext='.lzo'
                ;;

            none)
                csig='070701'
                ucmd=
                fext=
                ;;
        esac

        #========================================================================
        # Search for compressed cpio archive
        #========================================================================
        search=`grep -P -a -b -m 1 -o $csig $TEMP_DIR/$KERNEL_FILE | cut -f 1 -d : | head -1`
        pos=${search:-0}
        if [ ${pos} -gt 0 ]; then
            if [ ${pos} -le ${cpio_compressed_start:-0} ] || [ -z $cpio_compressed_start ];then
                cpio_compressed_start=$pos
                compression_name=$x
                compression_signature=$csig
                uncompress_cmd=$ucmd
                file_ext=$fext
				#break	
            fi
        fi
    done 

    [ $compression_name = "bzip" ] && cpio_compressed_start=$((cpio_compressed_start - 4))
    printhl "CPIO compression type detected = $compression_name | offset = $cpio_compressed_start"
}

function extract_cpio()
{
    if [ ! $compression_name = "none" ]; then
        printhl "Extracting $compression_name'd compressed CPIO image from kernel image (offset = $cpio_compressed_start)"
        dd if=$TEMP_DIR/$KERNEL_FILE of=$TEMP_DIR/$INITRAMFS_FILE$file_ext bs=$cpio_compressed_start skip=1 2>/dev/null >/dev/null
        $uncompress_cmd $TEMP_DIR/$INITRAMFS_FILE$file_ext 2>/dev/null >/dev/null

    else
        printhl "Extracting non-compressed CPIO image from kernel image (offset = $cpio_compressed_start)"
        dd if=$TEMP_DIR/$KERNEL_FILE of=$TEMP_DIR/${INITRAMFS_FILE}${file_ext} bs=$cpio_compressed_start skip=1 2>/dev/null >/dev/null
    fi
}

function expand_cpio_archive()
{
    printhl "Expanding CPIO archive: $INITRAMFS_FILE to $INITRAMFS_DIR."

    if [ -e $TEMP_DIR/$INITRAMFS_FILE ]; then
        mkdir -p $INITRAMFS_DIR
        cd $INITRAMFS_DIR
        $CPIO --quiet -i --make-directories --preserve-modification-time --no-absolute-filenames -F $TEMP_DIR/$INITRAMFS_FILE 2>/dev/null
    fi
}

function clean_up()
{
    rm -Rf $TEMP_DIR
}

#####################################################################################################

function detect_file_compression()
{
    filename=$1
    file_compressed_start=0
    file_compression_name=""
    file_compression_signature=""
    file_uncompress_cmd=""
    file_file_ext=""

    for x in none xz bzip gzip lzma lzo; do
        case $x in
            bzip)
                csig='\x{31}\x{41}\x{59}\x{26}\x{53}\x{59}'
                ucmd='bunzip2 -q'
                fext='.bz2'
                ;;

            gzip)
                csig='\x1F\x8B\x08'
                ucmd='gunzip -q'
                fext='.gz'
                ;;

            lzma)
                csig='\x{5D}\x{00}\x..\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}\x{FF}'
                ucmd='unlzma -q'
                fext='.lzma'
                ;;
            
            lzo)
            	csig='\211\114\132'
            	ucmd='lzop -d'
            	fext='.lzo'
                ;;
            
            xz)
            	csig='\x{FD}\x{37}\x{7A}\x{58}\x{5A}'
            	ucmd='xz -d'
            	fext='.xz'
                ;;

            none)
                csig='070701'
                ucmd=
                fext=
                ;;
        esac

        #========================================================================
        # Search for compressed payload archive
        #========================================================================
        search=`grep -P -a -b -m 1 -o $csig $filename | cut -f 1 -d : | head -1`
        pos=${search:0}
        if [ "${pos}" != "" ];then #&& [ ${pos} -ge 0 ]; then
            file_compressed_start=0
            file_compression_name=$x
            file_compression_signature=$csig
            file_uncompress_cmd=$ucmd
            file_file_ext=$fext
            if [ ${pos} -le ${file_compressed_start:-0} ] || [ -z $file_compressed_start ];then
                file_compressed_start=$pos
            fi
			break	
        fi
    done 

    [ $file_compression_name = "bzip" ] && file_compressed_start=$((file_compressed_start - 4))
}

function boot_extract()
{
    [ $boot_offset -le 0 ] && return 1
    [ $boot_len -le 0 ] && return 1

    dd bs=512 if=$zImage skip=$boot_offset count=$boot_len of=$BOOT_TAR > /dev/null 2>&1

    detect_file_compression $BOOT_TAR
    mv $BOOT_TAR $BOOT_TAR$file_file_ext
    printhl "Found payload: 'boot' compression=$file_compression_name offset=$boot_offset, len=$boot_len"

    printhl "Extracting '$BOOT_TAR$file_file_ext' ..."
    mkdir -p $PAYLOAD_DIR/boot
    cat $BOOT_TAR$file_file_ext | $file_uncompress_cmd | tar -xC $PAYLOAD_DIR/boot > /dev/null 2>&1
}

function recovery_extract()
{
    [ $recovery_offset -le 0 ] && return 1
    [ $recovery_len -le 0 ] && return 1

    dd bs=512 if=$zImage skip=$recovery_offset count=$recovery_len of=$RECOVERY_TAR > /dev/null 2>&1

    detect_file_compression $RECOVERY_TAR
    mv $RECOVERY_TAR $RECOVERY_TAR$file_file_ext
    printhl "Found payload: 'recovery' compression=$file_compression_name offset=$recovery_offset, len=$recovery_len"
   
    printhl "Extracting '$RECOVERY_TAR$file_file_ext' ..."
    mkdir -p $PAYLOAD_DIR/recovery
    cat $RECOVERY_TAR$file_file_ext | $file_uncompress_cmd | tar -xC $PAYLOAD_DIR/recovery > /dev/null 2>&1
}

function payload_extract()
{
    mkdir -p $PAYLOAD_DIR

    eval $(grep -a -m 1 -A 1 BOOT_IMAGE_OFFSETS $zImage | tail -n 1)
    if [ -z $recovery_offset ]; then
        recovery_offset=0
        recovery_len=0
    fi
    if [ -z $boot_offset ]; then
        boot_offset=0
        boot_len=0
    fi

    recovery_extract
    boot_extract
}

pre_clean
unpack_kernel
payload_extract
search_cpio
extract_cpio
expand_cpio_archive
[ -z $3 ] && clean_up