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SubjectRe: [PATCH] kheaders: making headers archive reproducible
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

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