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

[Jeremy Linton]

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@xxxxxxx> 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@xxxxxxx>
> > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > ---
> >   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