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

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Message-ID: <CAK7LNARBdF+7q03N07zz=pU4Ce59+O-_2Fb0vXLSrvgnj3zBeg@mail.gmail.com>
Date: Sun, 13 Jul 2025 14:45:24 +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
Subject: Re: [PATCH v2 1/1] scripts: add zboot support to extract-vmlinux

On Sun, Jul 13, 2025 at 3:50 AM Jeremy Linton <jeremy.linton@....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@....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@....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