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

[Nathan Chancellor <nathan@kernel.org>]

Hi Jeremy,

On Thu, May 22, 2025 at 12:29:41PM -0500, Jeremy Linton wrote:
> 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@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.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

Could these two lines be simplified to:

  if file $1 | grep 'Linux kernel.*boot executable Image' > /dev/null; 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
>