Commit 86cdd2fd authored by Dmitry Goldin's avatar Dmitry Goldin Committed by Masahiro Yamada
Browse files

kheaders: make headers archive reproducible 



In commit 43d8ce9d ("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 exposes them in procfs for use by userland tools.

The archive containing the header files has nondeterminism caused by
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 f7b101d3 ("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: default avatarDmitry Goldin <dgoldin+lkml@protonmail.ch>
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
parent d188b8c9

Documentation/kbuild/reproducible-builds.rst

+9 −4
Original line number Diff line number Diff line
@@ -16,16 +16,21 @@ the kernel may be unreproducible, and how to avoid them. 
Timestamps

----------



The kernel embeds a timestamp in two places:

The kernel embeds timestamps in three places:



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

  ``/proc/version``



* File timestamps in the embedded initramfs



By default the timestamp is the current time.  This must be overridden

using the `KBUILD_BUILD_TIMESTAMP`_ variable.  If you are building

from a git commit, you could use its commit date.

* If enabled via ``CONFIG_IKHEADERS``, file timestamps of kernel

  headers embedded in the kernel or respective module,

  exposed via ``/sys/kernel/kheaders.tar.xz``



By default the timestamp is the current time and in the case of

``kheaders`` the various files' modification times. This must

be overridden using the `KBUILD_BUILD_TIMESTAMP`_ variable.

If you are building from a git commit, you could use its commit date.



The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,

and enables warnings if they are used.  If you incorporate external

kernel/gen_kheaders.sh

+4 −1
Original line number Diff line number Diff line
@@ -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 normalize 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

CRA Git | Maintained and supported by SUSTech CRA and CCSE