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

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Message-ID: <14f2329f-e110-4f3f-976b-acb38d255798@arm.com>
Date: Mon, 16 Jun 2025 11:07:08 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, nathan@...nel.org,
 nicolas.schier@...ux.dev, linux-kernel@...r.kernel.org,
 Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH] scripts: add zboot support to extract-vmlinux

Hi,

Thanks for looking at this.

On 6/7/25 11:04 AM, Masahiro Yamada wrote:
> On Fri, May 23, 2025 at 2:29 AM Jeremy Linton <jeremy.linton@....com> wrote:
>>
>> Zboot compressed kernel images are used for arm kernels on various
>> distros.
> 
> Are you talking about arm 32 bit here?
> (arch/arm/boot/zImage)

No, it should be arm64.

> 
>> 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"
> 
> Are you talking about arm64 here?
> 
> I am confused, as arm64 adopts a simple-compressed image.

No, there is a CONFIG_EFI_ZBOOT, which is a EFI/PE image which self 
decompresses a contained kernel similar to x86, but is for !x86 EFI 
architectures. This patch extends this utility to work for those images 
as well.


> 
> 
> Apparently, this patch did not work for me.
> 
> $ ./scripts/extract-vmlinux  arch/arm/boot/zImage
> extract-vmlinux: Cannot find vmlinux.
> 
> The 'file' command says, it is "data".
> Is my 'file' command too old?
> 
> $ file arch/arm/boot/Image
> arch/arm/boot/Image: data
> 
> 
>> 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
>>
> 
>