#!/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
  # TODO: find a better to way to check that it's really vmlinux
  #       and not just an elf
  readelf -h $1 >/dev/null 2>&1 || return 1

  cat $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
    check_vmlinux $tmp
  done
}

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

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

# That didn't work, so retry after decompression.
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

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