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@xxxxxxx> 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@xxxxxxx>
> > ---
> >   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