linux-kernel - [PATCH] scripts: add zboot support to extract-vmlinux

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Message-ID: <20250522172941.1669424-1-jeremy.linton@arm.com>
Date: Thu, 22 May 2025 12:29:41 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: linux-kbuild@...r.kernel.org
Cc: masahiroy@...nel.org,
	nathan@...nel.org,
	nicolas.schier@...ux.dev,
	linux-kernel@...r.kernel.org,
	Jeremy Linton <jeremy.linton@....com>,
	Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH] scripts: add zboot support to extract-vmlinux

Zboot compressed kernel images are used for arm kernels on various
distros.

extract-vmlinux fails with those kernels because the wrapped image is
another PE. While this could be a bit confusing, the tools primary
purpose of unwrapping and decompressing the contained vmlinux image
makes it the obvious place for this functionality.

Add a 'file' check in check_vmlinux() that detects a contained PE
image before trying readelf. Recent file implementations output
something like:

"Linux kernel ARM64 boot executable Image, little-endian, 4K pages"

Which is also a stronger statement than readelf provides so drop that
part of the comment. At the same time this means that kernel images
which don't appear to contain a compressed image will be returned
rather than reporting an error. Which matches the behavior for
existing ELF files.

Signed-off-by: Jeremy Linton <jeremy.linton@....com>
Cc: Ard Biesheuvel <ardb@...nel.org>
---
 scripts/extract-vmlinux | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
index 8995cd304e6e..edda1abe226c 100755
--- a/scripts/extract-vmlinux
+++ b/scripts/extract-vmlinux
@@ -12,10 +12,11 @@

 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
+	file $1 |grep 'Linux kernel.*boot executable Image' > /dev/null
+	if [ "$?" -ne "0" ]; then
+		# Use readelf to check if it's a valid ELF, if 'file' fails
+		readelf -h $1 > /dev/null 2>&1 || return 1
+	fi

 	cat $1
 	exit 0
-- 
2.49.0