[Buildroot] [PATCH v2] fs/tar: explicitly set extended header values to ensure binary reproducibility

[Matthew Weber]

Atharva,

On Tue, Jul 2, 2019 at 12:37 PM Atharva Lele <itsatharva at gmail.com> wrote:
>
> Since we use --xattrs-include='*' to include all extended attributes,
> tar creates a PAX formatted archive. The archive metadata captures atime
> and ctime of files. To fix this, GNU recommends that we pass this added
> argument to tar to create binary reproducible packages. Setting of mtime
> is handled in fs/common.mk using touch on all files.
>
> Diffoscope output pre-change: https://gitlab.com/snippets/1871111
> Diffoscope output after change is blank i.e. binary reproducibile rootfs
> is created.
>
> GNU Recommendation: https://www.gnu.org/software/tar/manual/tar.html#SEC147
>
> Signed-off-by: Atharva Lele <itsatharva at gmail.com>

Reviewed-by: Matt Weber <matthew.weber at rockwellcollins.com>

> ---
> Changes v1 -> v2:
>   - Added comment about mtime handling
> ---
>  fs/tar/tar.mk | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/fs/tar/tar.mk b/fs/tar/tar.mk
> index 4c6327ace8..f6d11baa84 100644
> --- a/fs/tar/tar.mk
> +++ b/fs/tar/tar.mk
> @@ -8,6 +8,10 @@ TAR_OPTS := $(call qstrip,$(BR2_TARGET_ROOTFS_TAR_OPTIONS))
>
>  ROOTFS_TAR_DEPENDENCIES = $(BR2_TAR_HOST_DEPENDENCY)
>
> +ifeq ($(BR2_REPRODUCIBLE),y)
> +TAR_OPTS += --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0,ctime:=0
> +endif
> +
>  define ROOTFS_TAR_CMD
>         (cd $(TARGET_DIR); find -print0 | LC_ALL=C sort -z | \
>                 tar $(TAR_OPTS) -cf $@ --null --xattrs-include='*' --no-recursion -T - --numeric-owner)
> --
> 2.20.1
>
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-- 

Matthew Weber | Pr. Software Engineer | Commercial Avionics

COLLINS AEROSPACE

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