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

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Message-ID: <CAK7LNARG3wO_1R6_n1djbAQVx8=t0aMqAR4aaMUsRDBysSkkfA@mail.gmail.com>
Date: Wed, 25 Jun 2025 02:56:38 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Jeremy Linton <jeremy.linton@....com>
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

On Tue, Jun 17, 2025 at 1:09 AM Jeremy Linton <jeremy.linton@....com> wrote:
>
> 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.

The commit description does not explain why this is useful.

Extracing vmlinux ELF is useful for debugging purposes.

In this case, the extracted file is
arch/arm64/boot/vmlinux.bin, which is just a (zero-padded) binary.




>
> >
> >
> > 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
> >>
> >
> >
>
>


-- 
Best Regards
Masahiro Yamada