#!/bin/sh
# SPDX-License-Identifier: GPL-2.0-only
# ----------------------------------------------------------------------
# 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>
#
# ----------------------------------------------------------------------

check_vmlinux() {
	# Use readelf to check if it's a valid ELF
	readelf -h "$1" >/dev/null 2>&1 || return 1
	res=$(readlink -fn "$2")
	cat "$1" >"$res"
	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 $(LC_CTYPE=C tr "$1\n$2" "\n$2=" <"$img" | grep -abo "^$2"); do
		pos=${pos%%:*}
		tail -c+"$pos" "$img" | $3 >"$tmp" 2>/dev/null
		check_vmlinux "$tmp" "$res"
	done
}

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

res="vmlinux"
if [ $# -eq 2 ]; then
	res="$2"
fi

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

# That didn't work, so retry after decompression.
echo "[>] Attempting to write output into \"$res\""
try_decompress '\037\213\010' xy gunzip
try_decompress '\3757zXZ\000' abcde unxz
try_decompress 'BZh' xy bunzip2
try_decompress '\135\0\0\0' xxx unlzma
try_decompress '\211\114\132' xy 'lzop -d'
try_decompress '\002!L\030' xxx 'lz4 -d'
try_decompress '(\265/\375' xxx unzstd

# Finally check for uncompressed images or objects:
check_vmlinux "$img" "$res"

# Bail out:
echo "$me: Cannot find vmlinux." >&2
