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kheaders: rebuild kheaders_data.tar.xz when a file is modified within a minute

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When a header file is changed, kernel/gen_kheaders.sh may fail to update
kernel/kheaders_data.tar.xz.

[steps to reproduce]

[1] Build kernel/kheaders_data.tar.xz

  $ make -j$(nproc) kernel/kheaders.o
    DESCEND objtool
    INSTALL libsubcmd_headers
    CALL    scripts/checksyscalls.sh
    CHK     kernel/kheaders_data.tar.xz
    GEN     kernel/kheaders_data.tar.xz
    CC      kernel/kheaders.o

[2] Modify a header without changing the file size

  $ sed -i s/0xdeadbeef/0xfeedbeef/ include/linux/elfnote.h

[3] Rebuild kernel/kheaders_data.tar.xz

  $ make -j$(nproc) kernel/kheaders.o
    DESCEND objtool
    INSTALL libsubcmd_headers
    CALL    scripts/checksyscalls.sh
    CHK     kernel/kheaders_data.tar.xz

kernel/kheaders_data.tar.xz is not updated if steps [1] - [3] are run
within the same minute.

The headers_md5 variable stores the MD5 hash of the 'ls -l' output
for all header files. This hash value is used to determine whether
kheaders_data.tar.xz needs to be rebuilt. However, 'ls -l' prints the
modification times with minute-level granularity. If a file is modified
within the same minute and its size remains the same, the MD5 hash does
not change.

To reliably detect file modifications, this commit rewrites
kernel/gen_kheaders.sh to output header dependencies to
kernel/.kheaders_data.tar.xz.cmd. Then, Make compares the timestamps
and reruns kernel/gen_kheaders.sh when necessary. This is the standard
mechanism used by Make and Kbuild.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Masahiro Yamada 2025-06-09 01:59:55 +09:00
parent 694174f94e
commit 626c54af35
3 changed files with 63 additions and 74 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/.gitignore vendored
View File

@ -1,3 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
/config_data
/kheaders.md5
/kheaders-objlist
/kheaders-srclist

47
kernel/Makefile
View File

@ -158,11 +158,48 @@ filechk_cat = cat $<
$(obj)/config_data: $(KCONFIG_CONFIG) FORCE
$(call filechk,cat)
# kheaders_data.tar.xz
$(obj)/kheaders.o: $(obj)/kheaders_data.tar.xz
quiet_cmd_genikh = CHK $(obj)/kheaders_data.tar.xz
cmd_genikh = $(CONFIG_SHELL) $(srctree)/kernel/gen_kheaders.sh $@
$(obj)/kheaders_data.tar.xz: FORCE
$(call cmd,genikh)
quiet_cmd_kheaders_data = GEN $@
cmd_kheaders_data = "$<" "$@" "$(obj)/kheaders-srclist" "$(obj)/kheaders-objlist"
cmd_kheaders_data_dep = cat $(depfile) >> $(dot-target).cmd; rm -f $(depfile)
clean-files := kheaders_data.tar.xz kheaders.md5
define rule_kheaders_data
$(call cmd_and_savecmd,kheaders_data)
$(call cmd,kheaders_data_dep)
endef
targets += kheaders_data.tar.xz
$(obj)/kheaders_data.tar.xz: $(src)/gen_kheaders.sh $(obj)/kheaders-srclist $(obj)/kheaders-objlist $(obj)/kheaders.md5 FORCE
$(call if_changed_rule,kheaders_data)
# generated headers in objtree
#
# include/generated/utsversion.h is ignored because it is generated
# after gen_kheaders.sh is executed. (utsversion.h is unneeded for kheaders)
filechk_kheaders_objlist = \
for d in include "arch/$(SRCARCH)/include"; do \
find "$${d}/generated" ! -path "include/generated/utsversion.h" -a -name "*.h" -print; \
done
$(obj)/kheaders-objlist: FORCE
$(call filechk,kheaders_objlist)
# non-generated headers in srctree
filechk_kheaders_srclist = \
for d in include "arch/$(SRCARCH)/include"; do \
find "$(srctree)/$${d}" -path "$(srctree)/$${d}/generated" -prune -o -name "*.h" -print; \
done
$(obj)/kheaders-srclist: FORCE
$(call filechk,kheaders_srclist)
# Some files are symlinks. If symlinks are changed, kheaders_data.tar.xz should
# be rebuilt.
filechk_kheaders_md5sum = xargs -r -a $< stat -c %N | md5sum
$(obj)/kheaders.md5: $(obj)/kheaders-srclist FORCE
$(call filechk,kheaders_md5sum)
clean-files := kheaders.md5 kheaders-srclist kheaders-objlist

88
kernel/gen_kheaders.sh
View File

@ -4,79 +4,33 @@
# This script generates an archive consisting of kernel headers
# for CONFIG_IKHEADERS.
set -e
sfile="$(readlink -f "$0")"
outdir="$(pwd)"
tarfile=$1
tmpdir=$outdir/${tarfile%/*}/.tmp_dir
srclist=$2
objlist=$3
dir_list="
include/
arch/$SRCARCH/include/
"
dir=$(dirname "${tarfile}")
tmpdir=${dir}/.tmp_dir
depfile=${dir}/.$(basename "${tarfile}").d
# Support incremental builds by skipping archive generation
# if timestamps of files being archived are not changed.
# generate dependency list.
{
echo
echo "deps_${tarfile} := \\"
sed 's:\(.*\): \1 \\:' "${srclist}"
sed -n '/^include\/generated\/autoconf\.h$/!s:\(.*\): \1 \\:p' "${objlist}"
echo
echo "${tarfile}: \$(deps_${tarfile})"
echo
echo "\$(deps_${tarfile}):"
# 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 $all_dirs -name "*.h" -a \
! -path include/generated/utsversion.h -a \
! -path include/generated/autoconf.h |
xargs ls -l | md5sum | cut -d ' ' -f1)"
# Any changes to this script will also cause a rebuild of the archive.
this_file_md5="$(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 $tarfile"
} > "${depfile}"
rm -rf "${tmpdir}"
mkdir "${tmpdir}"
if [ "$building_out_of_srctree" ]; then
(
cd $srctree
for f in $dir_list
do find "$f" -name "*.h";
done | tar -c -f - -T - | tar -xf - -C "${tmpdir}"
)
fi
for f in $dir_list;
do find "$f" -name "*.h";
done | tar -c -f - -T - | tar -xf - -C "${tmpdir}"
# Always exclude include/generated/utsversion.h
# Otherwise, the contents of the tarball may vary depending on the build steps.
rm -f "${tmpdir}/include/generated/utsversion.h"
# shellcheck disable=SC2154 # srctree is passed as an env variable
sed "s:^${srctree}/::" "${srclist}" | tar -c -f - -C "${srctree}" -T - | tar -xf - -C "${tmpdir}"
tar -c -f - -T "${objlist}" | tar -xf - -C "${tmpdir}"
# Remove comments except SDPX lines
# Use a temporary file to store directory contents to prevent find/xargs from
@ -92,8 +46,4 @@ tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
--owner=0 --group=0 --sort=name --numeric-owner --mode=u=rw,go=r,a+X \
-I $XZ -cf $tarfile -C "${tmpdir}/" . > /dev/null
echo $headers_md5 > kernel/kheaders.md5
echo "$this_file_md5" >> kernel/kheaders.md5
echo "$(md5sum $tarfile | cut -d ' ' -f1)" >> kernel/kheaders.md5
rm -rf "${tmpdir}"