If you update the timestamp of KCONFIG_CONFIG without actually changing
anything, config_data.gz is re-generated and causes vmlinux to re-link.
When Link Time Optimization is enabled, unnecessary re-linking of
vmlinux is highly desirable since it adds several minutes to build time.
Avoid touching config_data.gz by using a script to compare the existing
config_data.gz, KCONFIG_CONFIG, or script itself to update only if any
is mismatched. The script follows gen_kheaders.sh approach for
determing in update is needed. The script intentionally avoids
re-compressing KCONFIG_CONFIG.
The .config can be touched, for instance, by a build script which
installs the default defconfig and then applies a defconfig fragment on
top.
For a simple example on my x86 machine, I modified x86 default defconfig to set
CONFIG_IKCONFIG=y and run:
make -j50 defconfig tiny.config vmlinux
make -j50 defconfig tiny.config vmlinux
With this patch, vmlinux is not re-built as a result of config_data.gz
change.
Changes in v2:
- Use md5 checksum to compare .config instead of gzip'ing again
Signed-off-by: Elliot Berman <eberman@xxxxxxxxxxxxxx>
---
kernel/.gitignore | 1 +
kernel/Makefile | 4 +++-
kernel/gen_config_data.sh | 31 +++++++++++++++++++++++++++++++
3 files changed, 35 insertions(+), 1 deletion(-)
create mode 100755 kernel/gen_config_data.sh
diff --git a/kernel/.gitignore b/kernel/.gitignore
index 78701ea..a191136 100644
--- a/kernel/.gitignore
+++ b/kernel/.gitignore
@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
+config_data.gz.md5
kheaders.md5
timeconst.h
hz.bc
diff --git a/kernel/Makefile b/kernel/Makefile
index 320f1f3..0784bf3d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -139,8 +139,10 @@ obj-$(CONFIG_SCF_TORTURE_TEST) += scftorture.o
$(obj)/configs.o: $(obj)/config_data.gz
targets += config_data.gz
+quiet_cmd_genicfg = CHK $(obj)/config_data.gz
+ cmd_genicfg = $(CONFIG_SHELL) $(srctree)/kernel/gen_config_data.sh $@ $<
$(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
- $(call if_changed,gzip)
+ $(call cmd,genicfg)
$(obj)/kheaders.o: $(obj)/kheaders_data.tar.xz
diff --git a/kernel/gen_config_data.sh b/kernel/gen_config_data.sh
new file mode 100755
index 00000000..e9ff193
--- /dev/null
+++ b/kernel/gen_config_data.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+# This script generates a compressed version of .config, if its checksum has changed
+set -e
+
+this_file="$(readlink -f "$0")"
+outfile=$1
+infile=$2
+
+config_md5="$(md5sum $infile | cut -d ' ' -f1)"
+# Any changes to this script will also cause a rebuild of config_data.
+this_file_md5="$(md5sum $sfile | cut -d ' ' -f1)"
+if [ -f $outfile ]; then outfile_md5="$(md5sum $outfile | cut -d ' ' -f1)"; fi
+
+if [ -f $outfile.md5 ] &&
+ [ "$(head -n 1 $outfile.md5)" = "$config_md5" ] &&
+ [ "$(head -n 2 $outfile.md5 | tail -n 1)" = "$this_file_md5" ] &&
+ [ "$(tail -n 1 $outfile.md5)" = "$outfile_md5" ]; then
+ exit
+fi
+
+if [ "${quiet}" != "silent_" ]; then
+ echo " GEN $outfile"
+fi
+
+${KGZIP} -c -n -f -9 $infile > $outfile
+
+echo "$config_md5" > $outfile.md5
+echo "$this_file_md5" >> $outfile.md5
+echo "$(md5sum $outfile | cut -d ' ' -f1)" >> $outfile.md5
--
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