rebuild-android-bootimg.sh

#!/bin/sh
# uses https://github.com/osm0sis/mkbootimg
# some guidance via stackoverflow.com/questions/29803996/repacak-existing-boot-img-using-mkbootimg-cyanogenmod-12-1-lollipop
set -ex
CM=~/Downloads/cm-12.1-20150730-UNOFFICIAL-fireballx.zip

# extract: unzip, unpackbootimg, zcat, cpio
test -d cm || (mkdir cm && cd cm && unzip $CM)
test -d unpack || (mkdir unpack && cd unpack && unpackbootimg -i ../cm/boot.img -o .)
test -d ramdisk-cpio || (mkdir ramdisk-cpio && cd ramdisk-cpio && zcat ../unpack/boot.img-ramdisk.gz > ramdisk.cpio)
test -d ramdisk || (mkdir ramdisk && cd ramdisk && cpio -iv < ../ramdisk-cpio/ramdisk.cpio)

# you may wish to modify the extracted ramdisk at this point.
# just rm -r any build-* directories, and rerun to reassemble

# repack: cpio, gz, mkbootimg, zip
test -d build-cpio || (mkdir build-cpio && cd ramdisk && find . -print | cpio --create --verbose -H newc > ../build-cpio/ramdisk)
test -d build-gz || (mkdir build-gz && cd build-gz && gzip -k ../build-cpio/ramdisk -c > ./ramdisk.gz)
test -d build-bootimg || (mkdir build-bootimg && \
mkbootimg --kernel unpack/boot.img-zImage \
          --ramdisk build-gz/ramdisk.gz \
          --cmdline "console=ttyHSL0,115200,n8 androidboot.hardware=qcom" \
          --base 0x80400000 \
          --pagesize 2048 \
          --kernel_offset 0x00008000 \
          --ramdisk_offset 0x01700000 \
          --tags_offset 0x00000100 \
          --output build-bootimg/boot2.img)
test -d build-cm || (mkdir build-cm && cd build-cm && unzip $CM && cp ../build-bootimg/boot2.img boot.img)
test -d build-zip || (mkdir build-zip && cd build-cm && zip -r ../build-zip/cm-hacked.zip .)

# unpackbootimg returns this information:
# BOARD_KERNEL_CMDLINE console=ttyHSL0,115200,n8 androidboot.hardware=qcom
# BOARD_KERNEL_BASE 80400000
# BOARD_NAME 
# BOARD_PAGE_SIZE 2048
# BOARD_KERNEL_OFFSET 00008000
# BOARD_RAMDISK_OFFSET 01700000
# BOARD_TAGS_OFFSET 00000100