shimboot/shim_utils.sh

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#!/bin/bash
#utilties for reading shim disk images
extract_initramfs() {
local kernel_bin="$1"
local working_dir="$2"
local output_dir="$3"
#first stage
local kernel_file="$(basename $kernel_bin)"
local binwalk_out=$(binwalk --extract $kernel_bin --directory=$working_dir --run-as=root)
local stage1_file=$(echo $binwalk_out | pcregrep -o1 "\d+\s+0x([0-9A-F]+)\s+gzip compressed data")
local stage1_dir="$working_dir/_$kernel_file.extracted"
local stage1_path="$stage1_dir/$stage1_file"
#second stage
binwalk --extract $stage1_path --directory=$stage1_dir --run-as=root > /dev/null
local stage2_dir="$stage1_dir/_$stage1_file.extracted/"
local cpio_file=$(file $stage2_dir/* | pcregrep -o1 "([0-9A-F]+):\s+ASCII cpio archive")
local cpio_path="$stage2_dir/$cpio_file"
rm -rf $output_dir
cat $cpio_path | cpio -D $output_dir -imd --quiet
}