linux/kernel/gen_kheaders.sh
Masahiro Yamada 2df8220cc5 kbuild: build init/built-in.a just once
Kbuild builds init/built-in.a twice; first during the ordinary
directory descending, second from scripts/link-vmlinux.sh.

We do this because UTS_VERSION contains the build version and the
timestamp. We cannot update it during the normal directory traversal
since we do not yet know if we need to update vmlinux. UTS_VERSION is
temporarily calculated, but omitted from the update check. Otherwise,
vmlinux would be rebuilt every time.

When Kbuild results in running link-vmlinux.sh, it increments the
version number in the .version file and takes the timestamp at that
time to really fix UTS_VERSION.

However, updating the same file twice is a footgun. To avoid nasty
timestamp issues, all build artifacts that depend on init/built-in.a
are atomically generated in link-vmlinux.sh, where some of them do not
need rebuilding.

To fix this issue, this commit changes as follows:

[1] Split UTS_VERSION out to include/generated/utsversion.h from
    include/generated/compile.h

    include/generated/utsversion.h is generated just before the
    vmlinux link. It is generated under include/generated/ because
    some decompressors (s390, x86) use UTS_VERSION.

[2] Split init_uts_ns and linux_banner out to init/version-timestamp.c
    from init/version.c

    init_uts_ns and linux_banner contain UTS_VERSION. During the ordinary
    directory descending, they are compiled with __weak and used to
    determine if vmlinux needs relinking. Just before the vmlinux link,
    they are compiled without __weak to embed the real version and
    timestamp.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
2022-09-29 04:40:15 +09:00

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#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
# This script generates an archive consisting of kernel headers
# for CONFIG_IKHEADERS.
set -e
sfile="$(readlink -f "$0")"
outdir="$(pwd)"
tarfile=$1
cpio_dir=$outdir/$tarfile.tmp
dir_list="
include/
arch/$SRCARCH/include/
"
# Support incremental builds by skipping archive generation
# if timestamps of files being archived are not changed.
# This block is useful for debugging the incremental builds.
# Uncomment it for debugging.
# if [ ! -f /tmp/iter ]; then iter=1; echo 1 > /tmp/iter;
# else iter=$(($(cat /tmp/iter) + 1)); echo $iter > /tmp/iter; fi
# find $all_dirs -name "*.h" | xargs ls -l > /tmp/ls-$iter
all_dirs=
if [ "$building_out_of_srctree" ]; then
for d in $dir_list; do
all_dirs="$all_dirs $srctree/$d"
done
fi
all_dirs="$all_dirs $dir_list"
# include/generated/utsversion.h is ignored because it is generated after this
# script is executed. (utsversion.h is unneeded for kheaders)
#
# When Kconfig regenerates include/generated/autoconf.h, its timestamp is
# updated, but the contents might be still the same. When any CONFIG option is
# changed, Kconfig touches the corresponding timestamp file include/config/*.
# Hence, the md5sum detects the configuration change anyway. We do not need to
# check include/generated/autoconf.h explicitly.
#
# Ignore them for md5 calculation to avoid pointless regeneration.
headers_md5="$(find $all_dirs -name "*.h" |
grep -v "include/generated/utsversion.h" |
grep -v "include/generated/autoconf.h" |
xargs ls -l | md5sum | cut -d ' ' -f1)"
# Any changes to this script will also cause a rebuild of the archive.
this_file_md5="$(ls -l $sfile | md5sum | cut -d ' ' -f1)"
if [ -f $tarfile ]; then tarfile_md5="$(md5sum $tarfile | cut -d ' ' -f1)"; fi
if [ -f kernel/kheaders.md5 ] &&
[ "$(head -n 1 kernel/kheaders.md5)" = "$headers_md5" ] &&
[ "$(head -n 2 kernel/kheaders.md5 | tail -n 1)" = "$this_file_md5" ] &&
[ "$(tail -n 1 kernel/kheaders.md5)" = "$tarfile_md5" ]; then
exit
fi
echo " GEN $tarfile"
rm -rf $cpio_dir
mkdir $cpio_dir
if [ "$building_out_of_srctree" ]; then
(
cd $srctree
for f in $dir_list
do find "$f" -name "*.h";
done | cpio --quiet -pd $cpio_dir
)
fi
# The second CPIO can complain if files already exist which can happen with out
# of tree builds having stale headers in srctree. Just silence CPIO for now.
for f in $dir_list;
do find "$f" -name "*.h";
done | cpio --quiet -pdu $cpio_dir >/dev/null 2>&1
# Remove comments except SDPX lines
find $cpio_dir -type f -print0 |
xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;'
# Create archive and try to normalize metadata for reproducibility.
# For compatibility with older versions of tar, files are fed to tar
# pre-sorted, as --sort=name might not be available.
find $cpio_dir -printf "./%P\n" | LC_ALL=C sort | \
tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
--owner=0 --group=0 --numeric-owner --no-recursion \
-I $XZ -cf $tarfile -C $cpio_dir/ -T - > /dev/null
echo $headers_md5 > kernel/kheaders.md5
echo "$this_file_md5" >> kernel/kheaders.md5
echo "$(md5sum $tarfile | cut -d ' ' -f1)" >> kernel/kheaders.md5
rm -rf $cpio_dir