Decompress kernels post hook

decompress_kernel

#!/bin/bash

KERNEL_VERSION="$1"
KERNEL_PATH="$2"

# extract-vmlinux is in /usr/local/bin
PATH="${PATH}:/usr/local/sbin"

# Ensure we have the extract-linux tool
if ! command -v extract-vmlinux > /dev/null; then
        echo >&2 "Command 'extract-vmlinux' is not available (https://raw.githubusercontent.com/torvalds/linux/master/scripts/extract-vmlinux),  Aborting"
        exit 1
fi

# The KERNEL_PATH must be valid
if [ ! -f "${KERNEL_PATH}" ]; then
        echo >&2 "Kernel file '${KERNEL_PATH}' not found. Aborting"
        exit 1
fi

# Create a temp file
TEMP_FILE=$(mktemp /tmp/decompress-kernel-XXXXX)
trap "rm -f ${TEMP_FILE}" 0

# If the given kernel file is still a bzimage see if its needs decompression
if echo "$(file -b "${KERNEL_PATH}")" | grep -q "^Linux kernel x86 boot executable bzImage"; then

        # Kernel is probably lz4 if there are lz4 headers in it
        #LZ4_HEADER="$(printf '\002!L\030')"
        #if ! grep -aqo "${LZ4_HEADER}" ${KERNEL_PATH}; then
        #        echo "No lz4 compression headers found, skipping..."
        #        exit 0
        #fi

        echo "Decompressing '${KERNEL_PATH}'..."
        # Extract the kernel and replace existing if successful
        if extract-vmlinux ${KERNEL_PATH} > ${TEMP_FILE}; then

                # Double check the kernel is a valid ELF image
                if ! readelf -h ${TEMP_FILE} > /dev/null; then
                        echo >&2 "Decompression of kernel file '${KERNEL_PATH}' failed!, not a valid ELF image"
                        exit 1
                fi

                echo "Decompression of kernel file '${KERNEL_PATH}' successful"
                cp -v ${TEMP_FILE} ${KERNEL_PATH}

        else
                echo >&2 "Decompression of kernel file '${KERNEL_PATH}' failed!"
                exit 1
        fi

# Perhaps its already been decompressed
elif echo "$(file -b "${KERNEL_PATH}")" | grep -q "^ELF 64-bit LSB executable"; then
        echo "Kernel file '${KERNEL_PATH}' appears to be decompressed already. skipping"

else
        echo >&2 "Unable to determine the state of kernel file '${KERNEL_PATH}'"
        exit 1
fi