linux-kernel - [PATCH] extract-vmlinux: Output used decompression method

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Message-ID: <X6OQ4pHdpreJtlTnf0tFEb4Uxz8T8gFv_7Yw6tpBK4ZBgHYjJr_URwUwCVynpkb-H8Yjk7DdBF01zY-sfqu_7N5trZQfcd6s_4PtdGlHtlA=@thiebaut.dev>
Date: Tue, 26 Aug 2025 19:23:49 +0000
From: Maxime Thiebaut <maxime@...ebaut.dev>
To: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>, Masahiro Yamada <masahiroy@...nel.org>
Cc: "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] extract-vmlinux: Output used decompression method

>From 3735cd80fa5baf3231f807174395a8252dfb0c4d Mon Sep 17 00:00:00 2001
From: Maxime Thiebaut <maxime+kernel@...ebaut.dev>
Date: Fri, 22 Aug 2025 10:40:03 +0200
Subject: [PATCH] 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@...ebaut.dev>
---
 scripts/extract-vmlinux | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
index 189956b5a5c8..266df9bc7a48 100755
--- a/scripts/extract-vmlinux
+++ b/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

base-commit: 6da752f55bc48fe2cf12ed208ab10295d796c2dd
-- 
2.50.1