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

[Jeremy Linton <jeremy.linton@arm.com>]

Hi,

Thanks for looking at this.

On 5/22/25 6:10 PM, Nathan Chancellor wrote:
> 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

Yes, but it needs, a '!', which applies to the last operator in the 
pipeline and for clarity should probably drop the redirection, so I 
think it ends up:

if ! file $1 | grep -q 'Linux kernel.*boot executable Image'; then

But it mixes the condition checking and the execution, which is common 
but maybe not the best idea.

Although, if I'm going to reroll this, i think the " Image" should be 
dropped since it can also have zImage and possibly other reports in the 
future and AFAIK there isn't any reason to exclude them.




> 
>> +		# 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
>>