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>
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index eecc186..8d98257 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -75,6 +75,8 @@
objs="${objs} .vmlinux.export.o"
fi
+ objs="${objs} init/version-timestamp.o"
+
if [ "${SRCARCH}" = "um" ]; then
wl=-Wl,
ld="${CC}"
@@ -213,19 +215,6 @@
exit 0
fi
-# Update version
-info GEN .version
-if [ -r .version ]; then
- VERSION=$(expr 0$(cat .version) + 1)
- echo $VERSION > .version
-else
- rm -f .version
- echo 1 > .version
-fi;
-
-# final build of init/
-${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1
-
#link vmlinux.o
${MAKE} -f "${srctree}/scripts/Makefile.vmlinux_o"
@@ -260,6 +249,8 @@
${MAKE} -f "${srctree}/scripts/Makefile.vmlinux" .vmlinux.export.o
fi
+${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
+
btf_vmlinux_bin_o=""
if is_enabled CONFIG_DEBUG_INFO_BTF; then
btf_vmlinux_bin_o=.btf.vmlinux.bin.o
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index ca40a52..f1a820d 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -1,14 +1,9 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
-TARGET=$1
-ARCH=$2
-SMP=$3
-PREEMPT=$4
-PREEMPT_DYNAMIC=$5
-PREEMPT_RT=$6
-CC_VERSION="$7"
-LD=$8
+UTS_MACHINE=$1
+CC_VERSION="$2"
+LD=$3
# Do not expand names
set -f
@@ -17,17 +12,6 @@
LC_ALL=C
export LC_ALL
-if [ -z "$KBUILD_BUILD_VERSION" ]; then
- VERSION=$(cat .version 2>/dev/null || echo 1)
-else
- VERSION=$KBUILD_BUILD_VERSION
-fi
-
-if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
- TIMESTAMP=`date`
-else
- TIMESTAMP=$KBUILD_BUILD_TIMESTAMP
-fi
if test -z "$KBUILD_BUILD_USER"; then
LINUX_COMPILE_BY=$(whoami | sed 's/\\/\\\\/')
else
@@ -39,63 +23,12 @@
LINUX_COMPILE_HOST=$KBUILD_BUILD_HOST
fi
-UTS_VERSION="#$VERSION"
-CONFIG_FLAGS=""
-if [ -n "$SMP" ] ; then CONFIG_FLAGS="SMP"; fi
+LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
+ | sed 's/[[:space:]]*$//')
-if [ -n "$PREEMPT_RT" ] ; then
- CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_RT"
-elif [ -n "$PREEMPT_DYNAMIC" ] ; then
- CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_DYNAMIC"
-elif [ -n "$PREEMPT" ] ; then
- CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT"
-fi
-
-# Truncate to maximum length
-UTS_LEN=64
-UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
-
-# Generate a temporary compile.h
-
-{ echo /\* This file is auto generated, version $VERSION \*/
- if [ -n "$CONFIG_FLAGS" ] ; then echo "/* $CONFIG_FLAGS */"; fi
-
- echo \#define UTS_MACHINE \"$ARCH\"
-
- echo \#define UTS_VERSION \"$UTS_VERSION\"
-
- printf '#define LINUX_COMPILE_BY "%s"\n' "$LINUX_COMPILE_BY"
- echo \#define LINUX_COMPILE_HOST \"$LINUX_COMPILE_HOST\"
-
- LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
- | sed 's/[[:space:]]*$//')
- printf '#define LINUX_COMPILER "%s"\n' "$CC_VERSION, $LD_VERSION"
-} > .tmpcompile
-
-# Only replace the real compile.h if the new one is different,
-# in order to preserve the timestamp and avoid unnecessary
-# recompilations.
-# We don't consider the file changed if only the date/time changed,
-# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for
-# reproducible builds with that value referring to a commit timestamp).
-# A kernel config change will increase the generation number, thus
-# causing compile.h to be updated (including date/time) due to the
-# changed comment in the
-# first line.
-
-if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
- IGNORE_PATTERN="UTS_VERSION"
-else
- IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED"
-fi
-
-if [ -r $TARGET ] && \
- grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \
- grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \
- cmp -s .tmpver.1 .tmpver.2; then
- rm -f .tmpcompile
-else
- echo " UPD $TARGET"
- mv -f .tmpcompile $TARGET
-fi
-rm -f .tmpver.1 .tmpver.2
+cat <<EOF
+#define UTS_MACHINE "${UTS_MACHINE}"
+#define LINUX_COMPILE_BY "${LINUX_COMPILE_BY}"
+#define LINUX_COMPILE_HOST "${LINUX_COMPILE_HOST}"
+#define LINUX_COMPILER "${CC_VERSION}, ${LD_VERSION}"
+EOF
