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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Thu, 3 Oct 2019 10:50:06 +0900
Message-ID: <CAK7LNAS1-HnsGTD1=sUm0L-gFjf3+q0qpuRQb1wREmzTs4UuVw@mail.gmail.com>
Subject: Re: [PATCH] kheaders: making headers archive reproducible
To:     Dmitry Goldin <dgoldin@protonmail.ch>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "joel@joelfernandes.org" <joel@joelfernandes.org>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Ben Hutchings <ben@decadent.org.uk>
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Hi Dmitry,


(+CC Ben Hutchings, who might be interested)


On Sun, Sep 22, 2019 at 10:38 PM Dmitry Goldin <dgoldin@protonmail.ch> wrote:
>
> From: Dmitry Goldin <dgoldin+lkml@protonmail.ch>
>
> In commit 43d8ce9d65a5 ("Provide in-kernel headers to make
> extending kernel easier") a new mechanism was introduced, for kernels
> >=5.2, which embeds the kernel headers in the kernel image or a module
> and exposed them in procfs for use by userland tools.
>
> The archive containing the header files has nondeterminism through the
> header files metadata. This patch normalizes the metadata and utilizes
> KBUILD_BUILD_TIMESTAMP if provided and otherwise falls back to the
> default behaviour.
>
> In commit f7b101d33046 ("kheaders: Move from proc to sysfs") it was
> modified to use sysfs and the script for generation of the archive was
> renamed to what is being patched.
>
> Signed-off-by: Dmitry Goldin <dgoldin+lkml@protonmail.ch>
> ---
>  kernel/gen_kheaders.sh | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)


Thanks, this produced the deterministic archive for me.


While you are here, could you also update the following hunk
in Documentation/kbuild/reproducible-builds.rst

---------->8---------------
The kernel embeds a timestamp in two places:

* The version string exposed by ``uname()`` and included in
  ``/proc/version``

* File timestamps in the embedded initramfs
---------->8---------------


With the documentation updated, I will pick it soon.

Thank you.


> diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
> index 9ff449888d9c..2e154741e3b2 100755
> --- a/kernel/gen_kheaders.sh
> +++ b/kernel/gen_kheaders.sh
> @@ -71,7 +71,10 @@ done | cpio --quiet -pd $cpio_dir >/dev/null 2>&1
>  find $cpio_dir -type f -print0 |
>         xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;'
>
> -tar -Jcf $tarfile -C $cpio_dir/ . > /dev/null
> +# Create archive and try to normalized metadata for reproducibility
> +tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
> +    --owner=0 --group=0 --sort=name --numeric-owner \
> +    -Jcf $tarfile -C $cpio_dir/ . > /dev/null
>
>  echo "$src_files_md5" >  kernel/kheaders.md5
>  echo "$obj_files_md5" >> kernel/kheaders.md5
> --
> 2.19.2
>
>
>


-- 
Best Regards
Masahiro Yamada