kumquat-buildroot/support/download/helpers
Yann E. MORIN 768f9f80f6 support/download: generate even more reproducible tarballs
When we generate the taballs off a local working copy of a VCS tree,
the umask is the one that we enforce in out top-level Makefile.

However, it is possible that a user manually tinkers in said working
copy (e.g. to check an upstream bug fix, or regression). If the user
umask is different from the one Buildroot enfirces, such tinkering
can impact the mode bits of the files, even if their content is not
modified.

When we eventually need to create a tarball from said working copy,
the VCS (e.g. git) will only be interested in checking whether the
content of the files have changed before chcking them out, and will
not look at, and restore/fix the mode bits.

As a consequence, we may create non-reproducible archives.

We fix that by enforcing the mode bits on the files before we create
the tarball: we disable the write and execute bits, and only set the
execute bit if the user execute bit is set.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Vincent Fazio <vfazio@xes-inc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
2023-09-14 23:02:07 +02:00

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# Generate a reproducible archive from the content of a directory
#
# $1 : input directory
# $2 : leading component in archive
# $3 : ISO8601 date: YYYY-MM-DDThh:mm:ssZZ
# $4 : output file
# $5... : globs of filenames to exclude from the archive, suitable for
# find's -path option, and relative to the input directory $1
#
# Notes :
# - the timestamp is internally rounded to the highest entire second
# less than or equal to the timestamp (i.e. any sub-second fractional
# part is ignored)
# - must not be called with CWD as, or below, the input directory
# - some temporary files are created in CWD, and removed at the end
#
# Example:
# $ find /path/to/temp/dir
# /path/to/temp/dir/
# /path/to/temp/dir/some-file
# /path/to/temp/dir/some-dir/
# /path/to/temp/dir/some-dir/some-other-file
#
# $ mk_tar_gz /path/to/some/dir \
# foo_bar-1.2.3 \
# 1970-01-01T00:00:00Z \
# /path/to/foo.tar.gz \
# '.git/*' '.svn/*'
#
# $ tar tzf /path/to/foo.tar.gz
# foo_bar-1.2.3/some-file
# foo_bar-1.2.3/some-dir/some-other-file
#
mk_tar_gz() {
local in_dir="${1}"
local base_dir="${2}"
local date="${3}"
local out="${4}"
shift 4
local glob tmp pax_options
local -a find_opts
for glob; do
find_opts+=( -or -path "./${glob#./}" )
done
# Drop sub-second precision to play nice with GNU tar's valid_timespec check
date="$(date -d "${date}" -u +%Y-%m-%dT%H:%M:%S+00:00)"
pax_options="delete=atime,delete=ctime,delete=mtime"
pax_options+=",exthdr.name=%d/PaxHeaders/%f,exthdr.mtime={${date}}"
tmp="$(mktemp --tmpdir="$(pwd)")"
pushd "${in_dir}" >/dev/null
# Enforce group/others mode bits
chmod -R go-wx+X .
# Establish list
find . -not -type d -and -not \( -false "${find_opts[@]}" \) >"${tmp}.list"
# Sort list for reproducibility
LC_ALL=C sort <"${tmp}.list" >"${tmp}.sorted"
# Create POSIX tarballs, since that's the format the most reproducible
tar cf - --transform="s#^\./#${base_dir}/#S" \
--numeric-owner --owner=0 --group=0 --mtime="${date}" \
--format=posix --pax-option="${pax_options}" \
-T "${tmp}.sorted" >"${tmp}.tar"
# Compress the archive
gzip -6 -n <"${tmp}.tar" >"${out}"
rm -f "${tmp}"{.list,.sorted,.tar}
popd >/dev/null
}
post_process_unpack() {
local dest="${1}"
local tarball="${2}"
local one_file
mkdir "${dest}"
tar -C "${dest}" --strip-components=1 -xzf "${tarball}"
one_file="$(find "${dest}" -type f -print0 |LC_ALL=C sort -z |sed 's/\x0.*//')"
touch -r "${one_file}" "${dest}.timestamp"
}
post_process_repack() {
local in_dir="${1}"
local base_dir="${2}"
local out="${3}"
local date
date="@$(stat -c '%Y' "${in_dir}/${base_dir}.timestamp")"
mk_tar_gz "${in_dir}/${base_dir}" "${base_dir}" "${date}" "${out}"
}
# Keep this line and the following as last lines in this file.
# vim: ft=bash