extract-vmlinux: Output used decompression method

When extract-vmlinux succeeds, it doesn't output which decompression method
was found at which offset. Adding this additional output in check_vmlinux()
helps troubleshooting and reverse-engineering images.

The last check_vmlinux() call was also quoted to accept spaces.

Signed-off-by: Maxime Thiebaut <maxime+kernel@thiebaut.dev>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Link: https://lore.kernel.org/r/X6OQ4pHdpreJtlTnf0tFEb4Uxz8T8gFv_7Yw6tpBK4ZBgHYjJr_URwUwCVynpkb-H8Yjk7DdBF01zY-sfqu_7N5trZQfcd6s_4PtdGlHtlA=@thiebaut.dev
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

scripts/extract-vmlinux

@@ -10,12 +10,15 @@
 #
 # ----------------------------------------------------------------------
 
+me=${0##*/}
+
 check_vmlinux()
 {
 	if file "$1" | grep -q 'Linux kernel.*boot executable' ||
 		readelf -h "$1" > /dev/null 2>&1
 	then
 		cat "$1"
+		echo "$me: Extracted vmlinux using '$2' from offset $3" >&2
 		exit 0
 	fi
 }
@@ -30,12 +33,11 @@ try_decompress()
 	do
 		pos=${pos%%:*}
 		tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
-		check_vmlinux $tmp
+		check_vmlinux $tmp "$3" $pos
 	done
 }
 
 # Check invocation:
-me=${0##*/}
 img=$1
 if	[ $# -ne 1 -o ! -s "$img" ]
 then
@@ -57,7 +59,7 @@ try_decompress '\002!L\030'   xxx   'lz4 -d'
 try_decompress '(\265/\375'   xxx   unzstd
 
 # Finally check for uncompressed images or objects:
-check_vmlinux $img
+check_vmlinux "$img" cat 0
 
 # Bail out:
 echo "$me: Cannot find vmlinux." >&2