#!/bin/sh

# ----------------------------------------------------------------------
# This file was taken from the Linux kernel source tree (scripts/extract-vmlinux)
# and has been adopted for the use within needrestart.
#
# extract-vmlinux - Extract uncompressed vmlinux from a kernel image
#
# Inspired from extract-ikconfig
# (c) 2009,2010    Dick Streefland <dick@streefland.net>
#
# (c) 2011         Corentin Chary <corentin.chary@gmail.com>
#
# Adopted for needrestart
# (c) 2016 - 2017  Thomas Liske <liske@ibh.de>
#
# Licensed under the GNU General Public License, version 2 (GPLv2).
# ----------------------------------------------------------------------

get_version()
{
    # search and output version string pattern,
    # prefer the final version string (linux 6.1+)
    grep -aoEm 1 'Linux version [[:digit:]].*#[^[:space:]]' "$1" && exit 0
    grep -aoEm 1 'Linux version [[:digit:]].*#' "$1" && exit 0
}

try_decompress()
{
    # The obscure use of the "tr" filter is to work around older versions of
    # "grep" that report the byte offset of the line instead of the pattern.

    # Try to find the header ($1) and decompress from here
    for pos in $(tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"); do
        pos=${pos%%:*}
        tail -c+"$pos" "$img" | $3 > "$tmp" 2>/dev/null
        get_version "$tmp"
    done
}

# Check invocation:
me=${0##*/}
img=$1
if [ $# -lt 1 ] || [ $# -gt 2 ] || [ ! -s "$img" ]; then
    echo "Usage: $me <kernel-image> [debug]" >&2
    exit 2
fi

if [ "$2" = "1" ]; then
    set -x
fi

# Prepare temp files:
tmp=$(mktemp)
trap 'rm -f "$tmp"' 0

# Initial attempt for uncompressed images or objects:
get_version "$img"

# That didn't work, so retry after decompression.
which gunzip  > /dev/null && try_decompress '\037\213\010' xy    gunzip
which unxz    > /dev/null && try_decompress '\3757zXZ\000' abcde unxz
which bunzip2 > /dev/null && try_decompress 'BZh'          xy    bunzip2
which unlzma  > /dev/null && try_decompress '\135\0\0\0'   xxx   unlzma
which lzop    > /dev/null && try_decompress '\211\114\132' xy    'lzop -d'