[PATCH v2 0/1] scripts: add zboot support to extract-vmlinux

[PATCH v2 0/1] scripts: add zboot support to extract-vmlinux

[Jeremy Linton]

Enhance the extract-vmlinux script for use with EFI_ZBOOT
compressed images.

v1->v2:
	Merge 'file' check with its 'if' condition.
	Invert the resulting condition and move copy block inside. 
	Tweak the commit message to clarify arm/arm64
	as well as how recent of a 'file' command is needed.

Jeremy Linton (1):
  scripts: add zboot support to extract-vmlinux

 scripts/extract-vmlinux | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

-- 
2.50.1

[PATCH v2 1/1] scripts: add zboot support to extract-vmlinux

[Jeremy Linton]

Zboot compressed kernel images are used for arm64 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 kernel 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 (FILES_39, Jun/2020) 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.

The extracted PE image can then be inspected, or used as would any
other kernel PE.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
---
 scripts/extract-vmlinux | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
index 8995cd304e6e..049bab337f0e 100755
--- a/scripts/extract-vmlinux
+++ b/scripts/extract-vmlinux
@@ -12,13 +12,12 @@
 
 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
-
-	cat $1
-	exit 0
+	if file "$1" | grep -q 'Linux kernel.*boot executable' \
+		|| readelf -h "$1" > /dev/null 2>&1
+	then
+		cat "$1"
+		exit 0
+	fi
 }
 
 try_decompress()
-- 
2.50.1

Re: [PATCH v2 1/1] scripts: add zboot support to extract-vmlinux

[Masahiro Yamada]

On Sat, Jul 12, 2025 at 1:26 AM Jeremy Linton <jeremy.linton@arm.com> wrote:
>
> Zboot compressed kernel images are used for arm64 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 kernel 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 (FILES_39, Jun/2020) 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.
>
> The extracted PE image can then be inspected, or used as would any
> other kernel PE.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  scripts/extract-vmlinux | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
> index 8995cd304e6e..049bab337f0e 100755
> --- a/scripts/extract-vmlinux
> +++ b/scripts/extract-vmlinux
> @@ -12,13 +12,12 @@
>
>  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
> -
> -       cat $1
> -       exit 0
> +       if file "$1" | grep -q 'Linux kernel.*boot executable' \

Sorry for my nit-picking, but I'd like to get rid of this back-slash
by breaking the line _after_ the OR operator, not before.

That is,


    if command1 ||
           command2
    then
         ...
    fi


rather than

    if command1 \
          || command2
    then
          ...
    fi






> +               || readelf -h "$1" > /dev/null 2>&1
> +       then
> +               cat "$1"
> +               exit 0
> +       fi
>  }
>
>  try_decompress()
> --
> 2.50.1
>


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2 1/1] scripts: add zboot support to extract-vmlinux

[Jeremy Linton]

Hi,

On 7/12/25 10:47 AM, Masahiro Yamada wrote:
> On Sat, Jul 12, 2025 at 1:26 AM Jeremy Linton <jeremy.linton@arm.com> wrote:
>>
>> Zboot compressed kernel images are used for arm64 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 kernel 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 (FILES_39, Jun/2020) 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.
>>
>> The extracted PE image can then be inspected, or used as would any
>> other kernel PE.
>>
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   scripts/extract-vmlinux | 13 ++++++-------
>>   1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
>> index 8995cd304e6e..049bab337f0e 100755
>> --- a/scripts/extract-vmlinux
>> +++ b/scripts/extract-vmlinux
>> @@ -12,13 +12,12 @@
>>
>>   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
>> -
>> -       cat $1
>> -       exit 0
>> +       if file "$1" | grep -q 'Linux kernel.*boot executable' \
> 
> Sorry for my nit-picking, but I'd like to get rid of this back-slash
> by breaking the line _after_ the OR operator, not before.
> 
> That is,
> 
> 
>      if command1 ||
>             command2
>      then
>           ...
>      fi
> 
> 
> rather than
> 
>      if command1 \
>            || command2
>      then
>            ...
>      fi

Moving the || is no problem, but I am/was under the impression that 
implicit line continuation is a posix shell gray area? Particularly when 
its outside of an explicit compound statement. This AFAIK was one of the 
things bash clarifed.

> 
>> +               || readelf -h "$1" > /dev/null 2>&1
>> +       then
>> +               cat "$1"
>> +               exit 0
>> +       fi
>>   }
>>
>>   try_decompress()
>> --
>> 2.50.1
>>
> 
> 

Re: [PATCH v2 1/1] scripts: add zboot support to extract-vmlinux

[Masahiro Yamada]

On Sun, Jul 13, 2025 at 3:50 AM Jeremy Linton <jeremy.linton@arm.com> wrote:
>
> Hi,
>
> On 7/12/25 10:47 AM, Masahiro Yamada wrote:
> > On Sat, Jul 12, 2025 at 1:26 AM Jeremy Linton <jeremy.linton@arm.com> wrote:
> >>
> >> Zboot compressed kernel images are used for arm64 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 kernel 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 (FILES_39, Jun/2020) 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.
> >>
> >> The extracted PE image can then be inspected, or used as would any
> >> other kernel PE.
> >>
> >> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> >> ---
> >>   scripts/extract-vmlinux | 13 ++++++-------
> >>   1 file changed, 6 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
> >> index 8995cd304e6e..049bab337f0e 100755
> >> --- a/scripts/extract-vmlinux
> >> +++ b/scripts/extract-vmlinux
> >> @@ -12,13 +12,12 @@
> >>
> >>   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
> >> -
> >> -       cat $1
> >> -       exit 0
> >> +       if file "$1" | grep -q 'Linux kernel.*boot executable' \
> >
> > Sorry for my nit-picking, but I'd like to get rid of this back-slash
> > by breaking the line _after_ the OR operator, not before.
> >
> > That is,
> >
> >
> >      if command1 ||
> >             command2
> >      then
> >           ...
> >      fi
> >
> >
> > rather than
> >
> >      if command1 \
> >            || command2
> >      then
> >            ...
> >      fi
>
> Moving the || is no problem, but I am/was under the impression that
> implicit line continuation is a posix shell gray area? Particularly when
> its outside of an explicit compound statement. This AFAIK was one of the
> things bash clarifed.


I believe this is clearly defined in POSIX [1]


2.10.2 Shell Grammar Rules:


and_or           :                         pipeline
                 | and_or AND_IF linebreak pipeline
                 | and_or OR_IF  linebreak pipeline
                 ;


linebreak        : newline_list
                 | /* empty */
                 ;


[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html



So, you can optionally put a linebreak
after the OF_IF token ('||' operator).







-- 
Best Regards
Masahiro Yamada