skitt/check-vmlinux Secret

## 64 changes: 64 additions & 0 deletions check-vmlinux
@@ -0,0 +1,64 @@

    #!/bin/sh
#!/bin/sh

    # SPDX-License-Identifier: GPL-2.0-only
# SPDX-License-Identifier: GPL-2.0-only

    # ----------------------------------------------------------------------
# ----------------------------------------------------------------------

    # check-vmlinux - Identify compression used for a kernel image
# check-vmlinux - Identify compression used for a kernel image

    #
#

    # Inspired from extract-ikconfig
# Inspired from extract-ikconfig

    # (c) 2009,2010 Dick Streefland <dick@streefland.net>
# (c) 2009,2010 Dick Streefland <dick@streefland.net>

    # (c) 2011      Corentin Chary <corentin.chary@gmail.com>
# (c) 2011      Corentin Chary <corentin.chary@gmail.com>

    # © 2019        Stephen Kitt <steve@sk2.org>
# © 2019        Stephen Kitt <steve@sk2.org>

    #
#

    # ----------------------------------------------------------------------
# ----------------------------------------------------------------------


    check_vmlinux()
check_vmlinux()

    {
{

    	# Use readelf to check if it's a valid ELF
	# Use readelf to check if it's a valid ELF

    	# TODO: find a better to way to check that it's really vmlinux
	# TODO: find a better to way to check that it's really vmlinux

    	#       and not just an elf
	#       and not just an elf

    	readelf -h $1 > /dev/null 2>&1 || return 1
	readelf -h $1 > /dev/null 2>&1 || return 1


    	echo The image was compressed using $2
	echo The image was compressed using $2

    	exit 0
	exit 0

    }
}


    try_decompress()
try_decompress()

    {
{

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


    	# Try to find the header ($1) and decompress from here
	# Try to find the header ($1) and decompress from here

    	for	pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
	for	pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`

    	do
	do

    		pos=${pos%%:*}
		pos=${pos%%:*}

    		tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
		tail -c+$pos "$img" | $3 > $tmp 2> /dev/null

    		check_vmlinux $tmp $4
		check_vmlinux $tmp $4

    	done
	done

    }
}


    # Check invocation:
# Check invocation:

    me=${0##*/}
me=${0##*/}

    img=$1
img=$1

    if	[ $# -ne 1 -o ! -s "$img" ]
if	[ $# -ne 1 -o ! -s "$img" ]

    then
then

    	echo "Usage: $me <kernel-image>" >&2
	echo "Usage: $me <kernel-image>" >&2

    	exit 2
	exit 2

    fi
fi


    # Prepare temp files:
# Prepare temp files:

    tmp=$(mktemp /tmp/vmlinux-XXX)
tmp=$(mktemp /tmp/vmlinux-XXX)

    trap "rm -f $tmp" 0
trap "rm -f $tmp" 0


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

    try_decompress '\037\213\010' xy    gunzip    gzip
try_decompress '\037\213\010' xy    gunzip    gzip

    try_decompress '\3757zXZ\000' abcde unxz      xz
try_decompress '\3757zXZ\000' abcde unxz      xz

    try_decompress 'BZh'          xy    bunzip2   bzip2
try_decompress 'BZh'          xy    bunzip2   bzip2

    try_decompress '\135\0\0\0'   xxx   unlzma    lzma
try_decompress '\135\0\0\0'   xxx   unlzma    lzma

    try_decompress '\211\114\132' xy    'lzop -d' lzop
try_decompress '\211\114\132' xy    'lzop -d' lzop

    try_decompress '\002!L\030'   xxx   'lz4 -d'  lz4
try_decompress '\002!L\030'   xxx   'lz4 -d'  lz4

    try_decompress '(\265/\375'   xxx   unzstd    zstd
try_decompress '(\265/\375'   xxx   unzstd    zstd


    # Finally check for uncompressed images or objects:
# Finally check for uncompressed images or objects:

    check_vmlinux $img none
check_vmlinux $img none


    # Bail out:
# Bail out:

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